As funções fisiológicas da proteína prion (PrPc) estão sob ampla investigação e caracterização, especialmente as funções associadas ao desenvolvimento cerebral. Destaca-se que a associação de PrPc com Stress Inducible Protein 1 (STI1), induz neuritogênese e neuroproteção via proteína cinase extracelular reguladora (ERK) e proteína cinase dependente de AMPc (PKA) respectivamente. O presente estudo avaliou como a expressão de PrP cem astrócitos pode modular a interação neurônioglia e o papel de STI1 como um fator autócrino em astrócitos. PrPc modula a interação neurônio-glia, a produção de fatores tróficos solúveis e a organização da laminina secretada na matriz extracelular pelos astrócitos. Desta forma, a expressão de PrP ctanto em astrócitos quanto em neurônios é essencial para a neuritogênese e sobrevivência neuronal. O papel autócrino de STI1 em astrócitos também foi demonstrado. A interação PrPc-STI1 previne a morte celular por ativação da via de PKA, e ativa a diferenciação astrocitária, de uma forma protoplasmática para uma fibrosa pela indução de ERK1/2. De acordo com estes resultados, um menor grau de diferenciação é encontrado em camundongos deficientes para PrPc. Estes apresentam uma expresão reduzida GFAP (proteína fibrilar acídica glial) e aumentada de vimentina e nestina em comparação com aqueles derivados de animais tipo-selvagem. STI1 promove ainda parada da proliferação astrocitária ativando a via de PKC de maneira independente de PrPc. O mecanismo pelo qual STI1 é secretada por astrócitos também foi avaliado e verificou-se que este é independente da via clássica mediada pelo complexo de Golgi. STI1 secretada é encontrada numa forma solúvel e em outra associada a componentes lipídicos e foram caracterizados por microscopia eletrônica como vesículas que variam entre 20-200nm. Dentre as vias de secreção não clássicas dependentes de lipídeos, a via de \"shedding\" de membrana foi descartada visto que STI1 não é secretada em associação com lipoproteínas. STI1 está presente em frações positivas para o receptor de transferrina, Hsp70, Hsp90 e PrPc, sugerindo composição exossomal. Esses resultados indicam que STI1 pode ser classificada como um fator trófico que associado ao seu \"receptor\" ou \"co-receptor\", PrPc, modula a sobrevivência e diferenciação tanto de neurônios quanto de astrócitos / The physiological functions of PrPc are under intense investigation and characterization, particularly those associated with brain development. In neurons, the association of PrPc with its ligand, STI1, induces neuritogenesis and neuroprotection via ERK and PKA signaling pathways, respectively. The present study evaluated whether PrPc expression in astrocytes modulates neuron-glia crosstalk and the autocrine role of STI1 in astrocytes. PrPc modulates neuron-glia interaction, the production and secretion of soluble factors, and the organization of the laminin in the extracellular matrix. PrPc expression in neurons and astrocytes is essential to neuritogenesis and neuronal survival. The autocrine role of STI1 in astrocytes was also demonstrated. The PrPc-STI1 interaction prevents cell death in a PKA-dependent manner, and induces astrocyte differentiation, from a flat to a process-bearing morphology in an ERK1/2 dependent manner. We showed that PrPccnull astrocytes presented a slower rate of astrocyte maturation than wild-type ones, with reduced expression of GFAP and increased vimentin and nestin expression. STI1 inhibited proliferation of both wild-type and PrPCnull astrocytes in a PKC-dependent manner. The mechanisms by which STI1 can be secreted by astrocytes was avaliated and we demonstrated that this secretion is independent on the classical secretory pathway mediated by the Golgi apparatus. Secreted STI1 is found in a soluble form and associated with lipidic compartments and we characterized by electron microscopy as vesicles that range from 20-200nm. Among the non-classical lipid-dependent secretory pathways, STI1 secretion by shedding was ruled out since STI1 was not secreted with lipoprotein fractions. On the other hand, STI1 is present in fractions that are positive for transferrin receptor, Hsp70, Hsp90 and PrPc, suggesting an exosome identity. Taken together, these data indicate that STI1 acts as a neurotrophic factor whose activity is dependent on the expression of PrP c at the neuronal surface, modulating differentiation and survival of both neurons and astrocytes

In der vorliegenden Arbeit habe ich wichtige Teilmechanismen der Erregungs-Sekretionskopplung in der Speicheldrüse der Schabe Periplaneta americana (L.) untersucht. Die Speicheldrüse ist von dopaminergen und serotonergen Fasern innerviert (Baumann et al., 2002). Beide Transmitter stimulieren eine unterschiedliche Reaktion der Drüse: Dopamin (DA) stimuliert die P-Zellen der Acini und die Ausführgangzellen, während Serotonin (5-HT) die P- und C-Zellen der Acini stimuliert, nicht jedoch die Ausführgangzellen. Der Endspeichel ist nach einer DA-Stimulierung proteinfrei. Dagegen enthält er nach einer 5-HT-Stimulierung Proteine, die von den C-Zellen sezerniert werden (Just & Walz, 1996). Im ersten Teil meiner Arbeit habe ich mittels Kapillarelektrophoretischer Analyse (CE-Analyse) die Elektrolytkonzentrationen im Endspeichel untersucht sowie die Raten der Flüssigkeitssekretion gemessen. Damit wollte ich klären, welche Transporter an der Sekretion des Primärspeichels und an dessen Modifikation beteiligt sind. Ausserdem wollte ich die Rolle der transportaktiven Epithelzellen der Ausführgänge für die Modifikation des Primärspeichels untersuchen. Dafür habe ich einen Vergleich der Elektrolytkonzentrationen im DA- und 5-HT-stimulierten Endspeichel durchgeführt. Der Elektrolytgehalt des DA- und 5-HT-stimulierten Endspeichels unterscheidet sich nicht signifikant voneinander. Er ist nach beiden Stimulierungen hypoosmotisch zum verwendeten Ringer. Die Ausführgangzellen werden durch DA stimuliert und modifizieren den Primärspeichel durch eine netto-Ionenreabsorption. Meine Versuche zeigen jedoch, dass auch die während einer 5-HT-Stimulierung der Drüse unstimulierten Ausführgangzellen den Primärspeichel modifizieren. In einer nachfolgenden Versuchsreihe habe ich den Einfluss von Ouabain, einem Hemmstoff der Na+-K+-ATPase, und Bumetanid, einem Hemmstoff des NKCC, auf die Raten der Flüssigkeitssekretion sowie den Elektrolytgehalt des Endspeichels untersucht. Ich habe gefunden, dass die Aktivität der Na+-K+-ATPase wichtig für die Modifikation des DA-stimulierten Primärspeichels ist. Im Gegensatz dazu ist sie für die Modifikation des 5-HT-stimulierten Primärspeichels nicht von Bedeutung. Bezüglich der Flüssigkeitssekretion habe ich keinen Einfluss der Na+-K+-ATPase-Aktivität auf die DA-stimulierten Sekretionsraten gefunden, dagegen ist die 5-HT-stimulierte Sekretionsrate in Anwesenheit von Ouabain gesteigert. Die Aktivität des NKCC ist für beide sekretorische Prozesse, die Ionen- und die Flüssigkeitssekretion, wichtig. Eine Hemmung des NKCC bewirkt eine signifikante Verringerung der Raten der Flüssigkeitssekretion nach DA- und 5-HT-Stimulierung sowie in beiden Fällen einen signifikanten Abfall der Ionenkonzentrationen im Endspeichel. Im zweiten Teil meiner Arbeit habe ich versucht, Änderungen der intrazellulären Ionenkonzentrationen in den Acinuszellen während einer DA- oder 5-HT-Stimulierung zu messen. Diese Experimente sollten mit der Methode des "ratiometric imaging" durchgeführt werden. Messungen mit dem Ca2+-sensitiven Fluoreszenzfarbstoff Fura-2 zeigten keinen globalen Anstieg in der intrazellulären Ca2+-Konzentration der P-Zellen. Aufgrund von Problemen mit einer schlechten Beladung der Zellen, einer starken und sich während der Stimulierung ändernden Autofluoreszenz der Zellen sowie Änderungen im Zellvolumen wurden keine Messungen mit Na+- und K+-sensitiven Fluoreszenzfarbstoffen durchgeführt. Im dritten Teil dieser Arbeit habe ich die intrazellulären Signalwege untersucht, die zwischen einer 5-HT-Stimulierung der Drüse und der Proteinsekretion vermitteln. Dazu wurde der Proteingehalt im Endspeichel biochemisch mittels eines modifizierten Bradford Assay gemessen. Eine erstellte Dosis-Wirkungskurve zeigt, dass die Rate der Proteinsekretion von der zur Stimulierung verwendeten 5-HT-Konzentration abhängt. In einer Serie von Experimenten habe ich die intrazellulären Konzentrationen von Ca2+, cAMP und / oder cGMP erhöht und anschließend den Proteingehalt im Endspeichel gemessen. Ein Anstieg der intrazellulären Ca2+-Konzentration aktiviert nur eine geringe Rate der Proteinsekretion. Dagegen kann die Steigerung der intrazellulären cAMP-Konzentration eine stärkere Proteinsekretion aktivieren, die sich nicht signifikant von der nach 5-HT-Stimulierung unterscheidet. Die cAMP-stimulierte Proteinsekretion kann durch gleichzeitige Erhöhung der intrazellulären Ca2+-Konzentration weiter gesteigert werden. Dagegen aktivierte eine Erhöhung der intrazellulären cGMP-Konzentration die Proteinsekretion nicht. Aufgrund dieser Ergebnisse postuliere ich die Existenz eines die Adenylatcyclase aktivierenden 5-HT-Rezeptors in der Basolateralmembran der C-Zellen. / The aim of this PhD-work was to investigate major mechanisms of excitation-secretion coupling in the salivary gland of the cockroach Periplaneta americana (L.). This salivary gland is innervated by dopaminergic and serotonergic fibres (Baumann et al., 2002). The two transmitters stimulate different processes in the gland: Dopamine (DA) stimulates the p-cells of the acini and the salivary duct cells, whereas 5-HT (serotonin) activates the p- and the c-cells of the acini, but not the salivary duct cells. Final saliva is completely protein-free after dopamine stimulation. It contains proteins, which are secreted by the c-cells of the acini, after a 5-HT-stimulation (Just & Walz, 1996). In the first part of my work I measured the electrolytic composition of the final saliva by capillary electrophoretic analysis and measured the rates of fluid secretion, in order to answer the following questions: 1.) Which transporters affect the production of primary saliva and its modification? 2.) What is the function of the transport-active salivary duct cells for the modification of the primary saliva? Electrolytic composition of the DA- and 5-HT-stimulated final saliva is not significantly different from each other, and is hypoosmotic to the Ringer used. Salivary duct cells are stimulated by DA and modify the primary saliva by a netto ion-reabsorption. My experiments also show that the duct cells, which are unstimulated during a 5-HT-stimulation of the gland, modify the primary saliva. In the next series of experiments I investigated the effects of ouabain, an inhibitor of the Na+-K+-ATPase, and bumetanide, an inhibitor of the NKCC on the rates of fluid secretion and the electrolytic composition of the final saliva. I found, that the activity of the Na+-K+-ATPase is important for the modification of DA-stimulated primary saliva during its flow through the stimulated duct system. In contrast, it is not important for modification of the 5-HT-stimulated primary saliva. Inhibition of the Na+-K+-ATPase does not affect rates of DA-stimulated fluid secretion, but it increases the rates of 5-HT-stimulated fluid secretion. Activity of the NKCC is important for both secretory processes: the ion and the fluid secretion. Inhibition of the NKCC results in a significant drop in the rates of fluid secretion after DA- and 5-HT-stimulation, as well as a drop in electrolytic concentrations in the saliva. In the second part of my work, I tried to measure changes in the intracellular ionic concentrations (Ca2+, Na+, and K+) within the acinar cells during a DA- or 5-HT-stimulation. The experiments should be performed by ratiometric imaging. Measurements with the Ca2+-sensitive dye Fura-2 did not show any global increase in the intracellular Ca2+-concentration in the p-cells of the acini. Problems concerning a bad loading of the cells, a strong autofluorescence which changed during the time course of the stimulation, as well as changes in the cell volume were the reason, that no measurements using Na+- or K+-sensitive dyes were performed. In the third part of my work I investigated the intracellular signalling pathways, which activate protein secretion after 5-HT-stimulation of the gland. A modified Bradford Assay was used for measuring the protein content in the final saliva. In a dose-response curve I showed that rates of protein secretion are dependent on the 5-HT-concentrations used to stimulate the glands. In another set of experiments I increased the intracellular concentrations of Ca2+, cAMP and / or cGMP, and measured the protein content in the final saliva. An increase in the intracellular Ca2+-concentration activates only a low rate of protein secretion. After an increase in the intracellular cAMP-concentration a much higher rate of protein secretion can be activated, which is not significantly different from the 5-HT stimulated rate of protein secretion. The cAMP-stimulated protein secretion can be further increased by a simultaneous rise in the intracellular Ca2+-concentration. In contrast, cGMP does not activate protein secretion. Therefore I propose the expression of an adenylyl cyclase activating 5-HT-receptor in the basolateral membrane of the protein secreting c-cells.

The versatile Escherichia coli facilitates protein expression with relative simplicity, high cell density on inexpensive substrates, well known genetics, variety of expression vectors, mutant strains, co-overexpression technology, extracytoplasmic secretion systems, and recombinant protein fusion partners. Although, the protocol is rather simple for soluble proteins, heterologous protein expression is frequently encountered by major technical limitations including inefficient translation, formation of insoluble inclusion bodies, lack of posttranslational modification mechanisms, degradation by host proteases, and impaired cell physiology due to host/protein toxicity, in achieving functional expression of stable, soluble, and bioactive protein.. In this thesis, model protein expression systems are used to address the technical issues for enhancing recombinant protein expression in E. coli. When yellow fluorescence protein (YFP) was displayed on E. coli cell surface, the integrity of the cell envelope was compromised and cell physiology was severely impaired, resulting in poor display performance, which was restored by the coexpression of Skp, a periplasmic chaperone. On the basis of monitoring the promoter activities of degP, rpoH, and cpxP under various culture conditions, it was demonstrated that the cell-surface display induced the σE extracytoplasmic stress response, and PdegP::lacZ was proposed to be a suitable “sensor” for monitoring extracytoplasmic stress. Intracellular proteolysis has been recognized as one of the key factors limiting recombinant protein production, particularly for eukaryotic proteins heterologously expressed in the prokaryotic expression systems of E. coli. Two amino acids, Leu149 and Val223, were identified as proteolytically sensitive when Pseudozyma antarctica lipase (PalB) was heterologously expressed in Escherichia coli. The functional expression was enhanced using the double mutant for cultivation. However, the recombinant protein production was still limited by PalB misfolding, which was resolved by DsbA coexpression. The study offers an alternative genetic strategy in molecular manipulation to enhance recombinant protein production in E. coli. To overcome the technical limitations of protein misfolding, ineffective disulfide bond formation, and protein instability associated with intracellular proteolysis in the functional expression of recombinant Pseudozyma antarctica lipase B (PalB) in Escherichia coli, an alternative approach was explored by extracellular secretion of PalB via two Sec-independent secretion systems, i.e. the α-hemolysin (Type I) and the modified flagellar (Type III) secretion systems, which can export proteins of interest from the cytoplasm directly to the exterior of the cell. Bioactive PalB was expressed and secreted extracellularly either as HlyA fusion (i.e. PalB-HlyA via Type I system) or an intact protein (via Type III system) with minimum impact on cell physiology. However, the secretion intermediates in the intracellular fraction of culture samples were non-bioactive even though they were soluble, suggesting that the extracellular secretion did mediate the development of PalB activity. PalB secretion via Type I system was fast with higher specific PalB activities but poor cell growth. On the other hand, the secretion via Type III system was slow with lower specific PalB activities but effective cell growth. Functional expression of lipase from Burkholderia sp. C20 (Lip) in various cellular compartments of Escherichia coli was explored. The poor expression in the cytoplasm was improved by several strategies, including coexpression of the cytoplasmic chaperone GroEL/ES, using a mutant E. coli host strain with an oxidative cytoplasm, and protein fusion technology. Fusing Lip with the N-terminal peptide tags of T7PK, DsbA, and DsbC was effective in boosting the solubility and biological activity. Non-fused Lip or Lip fusions heterologously expressed in the periplasm formed insoluble aggregates with a minimum activity. Biologically active and intact Lip was obtained upon the secretion into the extracellular medium using the native signal peptide and the expression performance was further improved by coexpression of the periplasmic chaperon Skp. The extracellular expression was even more effective when Lip was secreted as a Lip-HlyA fusion via the α-hemolysin transporter. Finally, Lip could be functionally displayed on the E. coli cell surface when fused with the carrier EstA.

The versatile Escherichia coli facilitates protein expression with relative simplicity, high cell density on inexpensive substrates, well known genetics, variety of expression vectors, mutant strains, co-overexpression technology, extracytoplasmic secretion systems, and recombinant protein fusion partners. Although, the protocol is rather simple for soluble proteins, heterologous protein expression is frequently encountered by major technical limitations including inefficient translation, formation of insoluble inclusion bodies, lack of posttranslational modification mechanisms, degradation by host proteases, and impaired cell physiology due to host/protein toxicity, in achieving functional expression of stable, soluble, and bioactive protein.. In this thesis, model protein expression systems are used to address the technical issues for enhancing recombinant protein expression in E. coli. When yellow fluorescence protein (YFP) was displayed on E. coli cell surface, the integrity of the cell envelope was compromised and cell physiology was severely impaired, resulting in poor display performance, which was restored by the coexpression of Skp, a periplasmic chaperone. On the basis of monitoring the promoter activities of degP, rpoH, and cpxP under various culture conditions, it was demonstrated that the cell-surface display induced the σE extracytoplasmic stress response, and PdegP::lacZ was proposed to be a suitable “sensor” for monitoring extracytoplasmic stress. Intracellular proteolysis has been recognized as one of the key factors limiting recombinant protein production, particularly for eukaryotic proteins heterologously expressed in the prokaryotic expression systems of E. coli. Two amino acids, Leu149 and Val223, were identified as proteolytically sensitive when Pseudozyma antarctica lipase (PalB) was heterologously expressed in Escherichia coli. The functional expression was enhanced using the double mutant for cultivation. However, the recombinant protein production was still limited by PalB misfolding, which was resolved by DsbA coexpression. The study offers an alternative genetic strategy in molecular manipulation to enhance recombinant protein production in E. coli. To overcome the technical limitations of protein misfolding, ineffective disulfide bond formation, and protein instability associated with intracellular proteolysis in the functional expression of recombinant Pseudozyma antarctica lipase B (PalB) in Escherichia coli, an alternative approach was explored by extracellular secretion of PalB via two Sec-independent secretion systems, i.e. the α-hemolysin (Type I) and the modified flagellar (Type III) secretion systems, which can export proteins of interest from the cytoplasm directly to the exterior of the cell. Bioactive PalB was expressed and secreted extracellularly either as HlyA fusion (i.e. PalB-HlyA via Type I system) or an intact protein (via Type III system) with minimum impact on cell physiology. However, the secretion intermediates in the intracellular fraction of culture samples were non-bioactive even though they were soluble, suggesting that the extracellular secretion did mediate the development of PalB activity. PalB secretion via Type I system was fast with higher specific PalB activities but poor cell growth. On the other hand, the secretion via Type III system was slow with lower specific PalB activities but effective cell growth. Functional expression of lipase from Burkholderia sp. C20 (Lip) in various cellular compartments of Escherichia coli was explored. The poor expression in the cytoplasm was improved by several strategies, including coexpression of the cytoplasmic chaperone GroEL/ES, using a mutant E. coli host strain with an oxidative cytoplasm, and protein fusion technology. Fusing Lip with the N-terminal peptide tags of T7PK, DsbA, and DsbC was effective in boosting the solubility and biological activity. Non-fused Lip or Lip fusions heterologously expressed in the periplasm formed insoluble aggregates with a minimum activity. Biologically active and intact Lip was obtained upon the secretion into the extracellular medium using the native signal peptide and the expression performance was further improved by coexpression of the periplasmic chaperon Skp. The extracellular expression was even more effective when Lip was secreted as a Lip-HlyA fusion via the α-hemolysin transporter. Finally, Lip could be functionally displayed on the E. coli cell surface when fused with the carrier EstA.

Although its highly infectious nature has led to its classification as a potential bio-terror threat, very little is known about the pathogenesis of Francisella. A complete understanding of the mechanisms employed by Francisella to gain residence and replicate within macrophages will provide valuable insight into the means by which F. tularensis, and other intracellular pathogens such as M. tuberculosis and L. pneumophila, invade host cells, secrete effectors, alter phagosome biogenesis and disrupt vesicle traficking. The overall theme of this dissertation is the analysis of genes encoded within a recently identified Francisella pathogenicity island (FPI). In particular, the chapters will focus on the identification, mutagenesis, and phenotypic analysis of Pathogenicity determinant protein D (pdpD), a ~135 kDa protein encoded within the FPI. Chapter 2 addresses the identification of the Francisella pathogenicity island, and the intramacrophage growth of several mutants found within this loci. One of the greatest strengths in determining the roles of putative virulence genes is the ability of researchers to alter and amplify nucleic acids in a highly developed model platform and subsequently introduce the altered genetic material into a pathogen. Although genetic transformation has been well developed and optimized in E. coli, where it is regularly used in cloning experiments, the introduction of DNA into Francisella has been a major deterrent in the mutagenesis of putative virulence factors. Chapter 3 focuses on engineered genetic elements and methods for transformation, antibiotic selection, deletion mutagenesis, and complementation in Francisella strains. The chromosomes of F. tularensis strains carry two identical copies of the Francisella pathogenicity island, and the FPI of North American-specific biotypes contain two genes, anmK and pdpD, that are not found in biotypes distributed over the entire Northern Hemisphere. Furthermore, unlike other known intracellular pathogens, F. tularensis lacks a functional type III or type IV secretion system, which are necessary for other bacterium to arrest maturation of their respective phagosomes. Chapter 4 focuses on the virulence contribution of anmK and pdpD using F. novicida, which is very closely related to F. tularensis but carries only one copy of the FPI. In addition, the outer membrane localization of PdpD is examined in deletions of FPI genes encoding proteins that are homologues of known components of Type VI secretion systems. Although each chapter is a continuum of research related to the Francisella pathogenicity island, each will be treated as a distinct work consisting of an introduction, materials and methods, results, and a discussion. Chapter 5 of this dissertation will consist of an overall conclusion section which will tie the 3 research chapters together as well as focus on future studies.

As funções fisiológicas da proteína prion (PrPc) estão sob ampla investigação e caracterização, especialmente as funções associadas ao desenvolvimento cerebral. Destaca-se que a associação de PrPc com Stress Inducible Protein 1 (STI1), induz neuritogênese e neuroproteção via proteína cinase extracelular reguladora (ERK) e proteína cinase dependente de AMPc (PKA) respectivamente. O presente estudo avaliou como a expressão de PrP cem astrócitos pode modular a interação neurônioglia e o papel de STI1 como um fator autócrino em astrócitos. PrPc modula a interação neurônio-glia, a produção de fatores tróficos solúveis e a organização da laminina secretada na matriz extracelular pelos astrócitos. Desta forma, a expressão de PrP ctanto em astrócitos quanto em neurônios é essencial para a neuritogênese e sobrevivência neuronal. O papel autócrino de STI1 em astrócitos também foi demonstrado. A interação PrPc-STI1 previne a morte celular por ativação da via de PKA, e ativa a diferenciação astrocitária, de uma forma protoplasmática para uma fibrosa pela indução de ERK1/2. De acordo com estes resultados, um menor grau de diferenciação é encontrado em camundongos deficientes para PrPc. Estes apresentam uma expresão reduzida GFAP (proteína fibrilar acídica glial) e aumentada de vimentina e nestina em comparação com aqueles derivados de animais tipo-selvagem. STI1 promove ainda parada da proliferação astrocitária ativando a via de PKC de maneira independente de PrPc. O mecanismo pelo qual STI1 é secretada por astrócitos também foi avaliado e verificou-se que este é independente da via clássica mediada pelo complexo de Golgi. STI1 secretada é encontrada numa forma solúvel e em outra associada a componentes lipídicos e foram caracterizados por microscopia eletrônica como vesículas que variam entre 20-200nm. Dentre as vias de secreção não clássicas dependentes de lipídeos, a via de \"shedding\" de membrana foi descartada visto que STI1 não é secretada em associação com lipoproteínas. STI1 está presente em frações positivas para o receptor de transferrina, Hsp70, Hsp90 e PrPc, sugerindo composição exossomal. Esses resultados indicam que STI1 pode ser classificada como um fator trófico que associado ao seu \"receptor\" ou \"co-receptor\", PrPc, modula a sobrevivência e diferenciação tanto de neurônios quanto de astrócitos / The physiological functions of PrPc are under intense investigation and characterization, particularly those associated with brain development. In neurons, the association of PrPc with its ligand, STI1, induces neuritogenesis and neuroprotection via ERK and PKA signaling pathways, respectively. The present study evaluated whether PrPc expression in astrocytes modulates neuron-glia crosstalk and the autocrine role of STI1 in astrocytes. PrPc modulates neuron-glia interaction, the production and secretion of soluble factors, and the organization of the laminin in the extracellular matrix. PrPc expression in neurons and astrocytes is essential to neuritogenesis and neuronal survival. The autocrine role of STI1 in astrocytes was also demonstrated. The PrPc-STI1 interaction prevents cell death in a PKA-dependent manner, and induces astrocyte differentiation, from a flat to a process-bearing morphology in an ERK1/2 dependent manner. We showed that PrPccnull astrocytes presented a slower rate of astrocyte maturation than wild-type ones, with reduced expression of GFAP and increased vimentin and nestin expression. STI1 inhibited proliferation of both wild-type and PrPCnull astrocytes in a PKC-dependent manner. The mechanisms by which STI1 can be secreted by astrocytes was avaliated and we demonstrated that this secretion is independent on the classical secretory pathway mediated by the Golgi apparatus. Secreted STI1 is found in a soluble form and associated with lipidic compartments and we characterized by electron microscopy as vesicles that range from 20-200nm. Among the non-classical lipid-dependent secretory pathways, STI1 secretion by shedding was ruled out since STI1 was not secreted with lipoprotein fractions. On the other hand, STI1 is present in fractions that are positive for transferrin receptor, Hsp70, Hsp90 and PrPc, suggesting an exosome identity. Taken together, these data indicate that STI1 acts as a neurotrophic factor whose activity is dependent on the expression of PrP c at the neuronal surface, modulating differentiation and survival of both neurons and astrocytes

The Golgi complex is an organelle responsible for receiving synthesized cargo from the endoplasmic reticulum for subsequent post-translations modifications, sorting and secretion. A family of proteins named Golgi Reassembly and Stacking Proteins (GRASP) is essential for the correct assembly and laterally tethering of the Golgi cisternae, a necessary structuration to keep this organelle working correctly. The GRASP structure is mainly composed of two regions: an N-terminal formed by two PDZ domains connected by a short loop (GRASP domain) and a non-conserved C-terminal region, rich in serine and proline residues. Although there are now a few crystal structures solved for the N-terminal domain, it is surprising to notice that no information is currently available regarding a full-length protein or even about dynamic and structural differences between the two PDZs in solution, which is the main functional region of this protein. Using a full-length GRASP model, we were capable of detecting the coexistence of regular secondary structures and large amounts of disordered regions. The overall structure is less compact than a regular globular protein and the high structural flexibility makes its hydrophobic core more accessible to solvent. GRASP coexist in a dynamic conformational ensemble of a µs-ms timescale. Our results indicate an unusual behavior of GRASP in solution, closely resembling a class of collapsed intrinsically disordered proteins called molten globule. We report here also the disorder-to-order transition propensities for a native molten globule-like protein in the presence of different mimetics of cell conditions. Changes in the dielectric constant (such as those experienced close to the membrane surface) seem to be the major factor capable of inducing several disorder-to-order transitions in GRASP, which seems to show very distinct behavior when in conditions that mimic the vicinity of the membrane surface as compared to those found when free in solution. Other folding factors such as molecular crowding, counter ions, pH and phosphorylation exhibit lower or no effect on GRASP secondary structure and/or stability. This is the first study focusing on understanding the disorder-to-order transitions of a molten globule structure without the need for any mild denaturing condition. Regarding the PDZs that form the GRASP domain, we observed that GRASPs are formed by a more unstable and flexible PDZ1 and much more stable and structurally well-behaved PDZ2. More than that, many of the unstable regions found in PDZ1 are in the predicted binding pocket, suggesting a structural promiscuity inside this domain that correlates with the functional promiscuity of interacting with multiple protein partners. This thesis presents the first structural characterization of a full-length GRASP, the first model of how GRASPs (or any molten globule-like protein) can be modulated by the cell during different cell functionalities and the first work in the community proving that the established idea that both PDZs are structurally equivalent is not completely right / O complexo de Golgi é um organela responsável pela recepção de carga sintetizada no retículo endoplasmático e por subsequente modificações pós-traducionais, classificação e secreção. Uma família de proteínas chamada Golgi Reassembly and Stacking Proteins (GRASP) é essencial para o correto empilhamento das cisternas e conexões laterais das pilhas do complexo de Golgi, uma estruturação necessária para manter essa organela funcionando corretamente. A estrutura das GRASPs é composta de duas regiões principais: uma extensão N-terminal formado por dois domínios PDZ conectados por um loop (domínio GRASP) e uma região C-terminal não conservada, rica em resíduos de serina e prolina. Embora existam algumas estruturas cristalográficas resolvidas para o domínio N-terminal, é surpreendente notar que não havia nenhuma informação na literatura sobre a construção inteira de um GRASP, ou mesmo um estudo detalhado sobre os PDZs no N-terminal em solução, que é a principal região funcional dessa proteína. Usando um modelo de GRASP em sua construção completa, fomos capazes de detectar a coexistência de estruturas secundárias regulares e grandes quantidades de regiões desordenadas. A estrutura é menos compacta do que uma proteína globular e a alta flexibilidade estrutural torna o seu núcleo hidrofóbico mais acessível ao solvente. GRASPs coexistem em um conjunto conformacional dinâmico numa escala de tempo característico de s-ms. Nossos resultados indicam um comportamento incomum da GRASP em solução, similar à de uma classe de proteínas intrinsicamente desordenadas colapsadas conhecidas como glóbulos fundidos. Nós relatamos também as propensões de transição estrutural do tipo desordem-ordem para uma proteína glóbulo fundido nativa, induzidas pela presença de diferentes miméticos de condições celulares especificas. A mudança na constante dielétrica do meio (como as experimentadas próximas à superfície da membrana biológica) é o principal modulador estrutural, capaz de induzir múltiplas transições desordem-ordem na GRASP, sugerindo um comportamento muito distinto quando em condições que imitam a vizinhança da superfície da membrana em comparação com os encontrados quando livre em solução. Outros fatores de enovelamento, tais como o molecular crowding, contra-ions, pH e a fosforilação exibem efeitos menores (ou nenhum) na estrutura secundária e/ou estabilidade da GRASP. Este é o primeiro estudo focado na compreensão das transições desordem-ordem em uma estrutura do tipo glóbulo fundido sem que houvesse a necessidade de qualquer condição desnaturante. Em relação aos PDZs que formam o domínio GRASP, observamos que as GRASPs são formadas por um PDZ1 mais instável e flexível e um PDZ2 muito mais estável e estruturalmente bem comportado. Mais do que isso, muitas das regiões instáveis encontradas no PDZ1 estão no predito bolsão de ligação, sugerindo uma promiscuidade estrutural dentro desse domínio que se correlaciona com a promiscuidade funcional de interação com múltiplos parceiros proteicos. É apresentado nesta tese a primeira caracterização estrutural de uma GRASP em sua forma completa, o primeiro modelo de como as GRASPs (ou qualquer proteína em forma de glóbulo fundido) pode ser modulada estruturalmente pela célula durante diferentes funcionalidades e o primeiro trabalho na comunidade provando que a estabelecido ideia de que ambos os PDZs são estruturalmente equivalentes não é completamente correta

Background: Cyclodextrin glucanotransferases (CGTases) catalyze the synthesis of cyclodextrins, cyclic oligosaccharides composed of glucose monomers that find applications in the pharmaceutical, food, and cosmetic industries. An economic application of these industrially important enzymes requires their efficient production and recovery. In this study, the effect of Sec-type signal peptides on the recombinant expression of a CGTase derived from Bacillus sp. G825-6 was investigated in Escherichia coli BL21(DE3) using a codon-adapted gene. In addition, a novel purification method for the CGTase using starch adsorption was developed. Results: Expression vectors encoding N-terminal PelB, DacD, and the native Bacillus sp. G825-6 CGTase signal peptides (SP) were constructed for the recombinant CGTase. With the DacD SP derived from E. coli, a 3.9- and 3.1-fold increase in total enzyme activity was obtained compared to using the PelB and the native CGTase SP, respectively. DacD enabled a 7.3-fold increase of activity in the extracellular fraction after induction for 24 h compared to the native CGTase SP. After induction for 48 h, 75% of the total activity was detected in the extracellular fraction. By a batch wise adsorption to starch, the extracellular produced CGTase could be purified to homogeneity with a yield of 46.5% and a specific activity of 1637 U/mg. Conclusions: The signal peptide DacD promoted the high-level heterologous extracellular expression of a recombinant CGTase from Bacillus sp. G825-6 with a pET20b(+) vector in E. coli BL21(DE3). A protocol based on starch adsorption enabled a fast and efficient purification of the recombinant enzyme.

Chez Bacillus subtilis nous avons identifié un complexe protéique membranaire impliquant une protéine inconnue, YteJ, et une autre protéine membranaire, SppA, une signal peptide peptidase également impliquée dans la résistance aux peptides antibactériens de la famille des lantibiotiques. Après délétion des gènes correspondant, nous avons montré que les deux protéines sont impliquées dans cette résistance. Dans la souche ΔsppA, la surexpression ectopique de SppA a non seulement restauré la résistance, mais elle a également induit la formation de cellules allongées, un phénotype supprimé par la surexpression simultanée de YteJ. L'expression de versions tronquées de YteJ a mis en évidence le rôle inhibiteur d'un domaine spécifique de YteJ. Enfin, des études biochimiques in vitro ont confirmé que l'activité de la protéase SppA était fortement réduite par la présence de YteJ, confirmant l'hypothèse d'une inhibition par YteJ. Nos études in vivo et in vitro ont montré que YteJ, via l'un de ses domaines, agit comme régulateur négatif de l'activité protéase de SppA dans ce complexe. En conclusion, nous avons montré que le complexe SppA/YteJ est impliqué dans la résistance aux lantibiotiques à travers l’activité protéase de SppA, elle-même régulée par YteJ. / We have identified a membrane protein complex of Bacillus subtilis involving an unknown protein, YteJ, and SppA, a membrane protein first described as a signal peptide peptidase and later shown to be also involved in the resistance to antibacterial peptides of the lantibiotic family. Using deletion mutant strains, we showed that both proteins are involved in this resistance. In the ΔsppA strain, the ectopic overexpression of SppA not only restored the resistance, it also induced the formation of elongated cells, a phenotype suppressed by the simultaneous overexpression of YteJ. Furthermore, the expression of truncated versions of YteJ pinpointed the inhibitory role of a specific domain of YteJ. Finally, in vitro biochemical studies showed that SppA protease activity was strongly reduced by the presence of YteJ, supporting the hypothesis of an inhibition by YteJ. Our in vivo and in vitro studies showed that YteJ, via one of its domain, acts as a negative regulator of the protease activity of SppA in this complex. In conclusion, we have shown that SppA/YteJ complex is involved in lantibiotic resistance through the protease activity of SppA, which is regulated by YteJ.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Mycobacterium tuberculosis, the causative agent of tuberculosis disease, contains five copies of the ESAT-6 gene cluster, each encoding a dedicated ESX protein secretion system which has been defined as a novel Type-VII secretion system. The ESX have been implicated in virulence and survival of M. tuberculosis, and as such present a promising target for novel treatment interventions. This study has investigated the evolution, regulation, functions and substrates of the ESX secretion systems. The evolutionary history of the ESX secretion systems was established using in silico and phylogenetic analyses of the sequenced mycobacteria, closely related actinomycetes and WXG-FtsK clusters from other bacteria. The ESX-4 gene cluster appears to have evolved with the start of the evolution of the mycomembrane, followed by the duplication of ESX-3, which marks the evolution of the genus Mycobacterium. The ESX-1 duplication occurred next, followed by ESX-2 and ESX-5 which occur only in the slow growing mycobacteria. Five additional ESX gene clusters were newly identified and named ESX-P1 to - P5. These additional ESX clusters occur, or are predicted to occur, on plasmid DNA, and appear to be progenitors of the genomic ESX-1 to -5 gene clusters, possibly indicating a plasmid-mediated mechanism of ESX duplication and evolution. The promoters expressing the M. tuberculosis ESX-1 to ESX-5 secretion systems were investigated using a promoter probe assay, and characterised using in silico analyses. Promoters were identified for ESX-1, -2, -3 and -5. The functions of the mycobacterial ESX secretion systems were investigated using whole proteomic, secretomic and metabolomic analyses of the fast growing, non-pathogenic M. smegmatis, which contains three of the ESX secretion systems, ESX-1, 3, and 4. ESX knockout strains of M. smegmatis were generated and used in comparative analyses with wild-type M. smegmatis. ESX-1 was highly expressed in wild-type M. smegmatis, however no specific pathways showed considerable variation when ESX-1 was deleted. Deletion of ESX-3 resulted in substantial variation to multiple cellular pathways, including amino acid, carbohydrate and fatty acid metabolism and oxidative stress. These and other differences indicate possible perturbed polyamine metabolism in the absence of ESX-3. Although no ESX-4 protein components were detected in wild type M. smegmatis, the ESX-4 knockout displayed substantial proteomic variation. Reduced levels of ESX-3 component proteins in the ESX-4 knockout suggest that ESX-4 influences ESX-3 expression. Other variation linked ESX-4 to cell division and molybdenum metabolism. Secretomic analyses of wild-type and ESX knockout M. smegmatis strains were used to search for novel substrates of the M. smegmatis ESX secretion systems. No prototype ESX substrates were identified in the culture filtrates, however 10 possible substrates of the ESX-1, -3 and -4 secretion systems, containing the general ESX secretion signal, YxxxD/E, were identified. The functions of some of these proteins correlate with the ESX functions identified in the proteomic and metabolomic analyses. This study sets the groundwork for future work in understanding the functional roles and expression patterns of these ESX secretion systems and in using global proteomic and metabolomic analyses to understand cellular changes in response to specific signals or genomic changes. / AFRIKAANSE OPSOMMING: Mycobacterium tuberculosis, die veroorsakende agent van tuberkulose, bevat vyf kopieë van die ESAT-6 geengroep, wat elk 'n toegewyde ESX proteïen sekresiesisteem, omskryf as 'n nuwe Tipe-VII sekresiestelsel, kodeer. Die ESX sekresiesisteme is betrokke by virulensie en oorlewing van M. tuberculosis, en is dus belowende teikens vir nuwe behandelings. Hierdie studie het die evolusie, regulasie, funksies en substrate van die ESX sekresiesisteme ondersoek. Die evolusionêre geskiedenis van die ESX sekresiesisteme is bepaal met behulp van in silico en filogenetiese analises van die volgordebepaalde mikobakterieë, nouverwante actinomisete en WXG-FtsK groepe van ander bakterieë. Die ESX-4 geengroep het saam met die evolusie van die mikomembraan ontwikkel, gevolg deur die duplisering van ESX-3, wat die evolusie van die genus Mycobacterium merk. Die ESX-1 duplisering het volgende plaasgevind, gevolg deur ESX-2 en ESX-5, wat slegs in die stadiggroeiende mikobakterieë voorkom. Vyf addisionele ESX geengroepe is nuut geïdentifiseer in hierdie studie en is ESX-P1 tot -P5 genoem. Hierdie addisionale ESX groepe is op, of word voorspel om op, plasmied DNS voor te kom, en mag voorlopers van die genomiese ESX-1 tot -5 geengroepe wees, wat moontlik dui op 'n plasmied-gemedieërde meganisme van ESX duplisering en evolusie. Die promoters wat verantwoordelik is vir die uitdrukking van die M. tuberculosis ESX-1 tot ESX-5 sekresiesisteme is ondersoek deur middel van 'n promoter aktiwiteitstoets, en gekarakteriseer deur in silico analises. Promoters is geidentifiseer vir ESX-1, -2, -3 en -5. Die funksies van die mikobakteriële ESX sekresiesisteme is ondersoek deur proteomiese, sekretomiese en metabolomiese analises van die vinnig-groeiende, nie-patogeniese mikobakterium M. smegmatis, wat ESX- 1, -3 en -4 sekresiesisteme besit. ESX uitslaanmutante van M. smegmatis is gegenereer en gebruik in die vergelykende analises met die wilde-tipe M. smegmatis. ESX-1 is hoogs uitgedruk in wilde-tipe M. smegmatis, maar geen spesifieke metabolise weë het aansienlike variasie getoon wanneer ESX-1 verwyder is. Delesie van ESX-3 het gelei tot aansienlike variasie in verskeie sellulêre weë, insluitend aminosuur-, koolhidraat- en vetsuur-metabolisme en oksidatiewe stres. Hierdie en ander verskille dui op moontlike versteurde poli-amien metabolisme in die afwesigheid van ESX-3. Hoewel geen ESX-4 proteïenkomponente opgespoor is in wilde-tipe M. smegmatis nie, vertoon die ESX-4 uitslaanmutant aansienlike proteomiese variasie. Laer vlakke van ESX-3 proteïne dui daarop dat ESX-4 die uitdrukking van ESX-3 beinvloed. Baie van die proteomiese variasie kan geassosieer word met verlaagde ESX-3 uitdrukking, maar ander variasie mag ESX-4 koppel met seldeling en molibdeen metabolisme. Sekretomiese analises van wilde-tipe en ESX uitslaanmutant M. smegmatis stamme is gebruik om nuwe substrate van die M. smegmatis ESX sekresiesisteme te identifiseer. Geen prototipe ESX substrate is geïdentifiseer in die kultuurfiltraat, maar 10 moontlike substrate van die ESX-1, -3 en -4 sekresiesisteme, met die algemene ESX sekresiesein, YxxxD/E, is geïdentifiseer. Die funksies van sommige van hierdie proteïene korreleer met die funksies geïdentifiseer in die proteomiese en metabolomiese analises. Hierdie studie stel die grondslag vir toekomstige werk in die begrip van die funksionele rol en uitdrukkingspatrone van die ESX sekresiesisteme en in die gebruik van globale proteomiese en metabolomiese analises om sellulêre veranderinge in reaksie op spesifieke seine of genomiese veranderinge te verstaan. / The National Research Foundation / German Academic Exchange Service (DAAD), / The Harry Crossley Foundation / The Ernst and Ethel Erikson Trust / Stellenbosch University