As toxinas de veneno de serpentes têm como principal função alterar a homeostase das presas para fins de alimentação ou defesa. O estudo aprofundado da composição do veneno de serpentes é importante para a produção de soros antiofídicos mais eficientes, para a descoberta de novos fármacos e na compreensão de processos biológicos, ecológicos e evolutivos. As pesquisas com toxinas têm mostrado uma versatilidade natural, refinada pela evolução, na diversificação de funções em famílias de proteínas recrutadas de suas funções endógenas, por meio de sucessivas duplicações e acumulo de mutações levando a uma evolução acelerada. A miríade de toxinas disponíveis e sua diversidade de funções ainda não foram completamente descritas. A combinação das análises em larga escala do transcriptoma de novo da glândula de veneno e do proteoma do veneno permite elaborar um perfil mais completo do toxinoma do veneno, permitindo inclusive um aumento na sensibilidade da detecção de toxinas pouco representadas e inesperadas nos venenos. O objetivo geral deste estudo foi analisar o toxinoma do veneno de uma das mais perigosas espécies australianas, a Pseudonaja textilis (Elapidae). Foi possível identificar no veneno as toxinas: fatores de coagulação de veneno do complexo protrombinase, subunidades de fosfolipases A2 (PLA2) da neurotoxina textilotoxin e PLA2 de atividade procoagulante, neurotoxinas tipo three-finger toxin (3FTx), inibidores de protease do tipo-kunitz textilinin, e pela primeira vez, uma nova variante de 3FTx, lectinas tipo C, CRiSP além de indícios de toxinas de lagarto Heloderma e outras proteínas candidatas a toxinas como calreticulin e dipeptidase 2. Metaloproteinases, pouco estudadas em Elapidae, foram clonadas e detectadas no veneno por ensaios de fracionamento e imunoreatividade. A análise do transcriptoma identificou novas isoformas e variantes de toxinas, principalmente das 3FTx e dos inibidores de serinoproteases, assim como transcritos de toxinas que não foram detectadas no veneno e que merecem mais investigações. O quadro de sintomas com acidentes em humanos é bem explicado pelas toxinas identificadas, porém, em seu habitat natural, as toxinas pouco conhecidas e até então não descritas devem ter funções importantes e específicas na predação. Identificar esta diversidade de variantes é importante para entender o modo de ação das toxinas. / Snake venom toxins alter prey homeostasis for feeding or defense. In depth studies of venom composition are important for better antivenom production, for new drugs lead and discovery and for better understanding of biological, ecological and evolutionary processes. Research on toxins have shown the natures way of innovating, refined by evolution, diversifying functions of protein families recruited from their endogenous function to the venom gland by successive gene duplication and mutation accumulation, leading to an accelerated evolution. A myriad of available toxins and diversity of functions is still available for discovery. Combining high throughput techniques such as venom gland de novo transcriptomics and venom proteomics, one can assess and observe a more complete profile of the snake toxinome, additionally allowing an upscale in low represented and unexpected toxin detection. The aim of this project was to investigate the venom toxinome of one of the most dangerous Australian species, Pseudonaja textilis (Elapidae). The toxins identified in it venom was: protrombinase complex coagulation factors, neurotoxic textilotoxin phospholipase A2 (PLA2) subunits and procoagulant PLA2, neurotoxic three-finger toxins (3FTx), Kunitz-type protease inhibitor textilinin, and for the first time, a new long 3FTx, C-type lectins, CRiSPs, as well as evidences of lizard toxins from Heloderma genus and other toxin candidates calreticulin and dipeptidase 2. Metalloproteinases, little investigated in Elapidae, was cloned and detected in the venom after fractionation and immunoassay. The transcriptome revealed new toxin variants and isoforms, specially 3FTx and serine protease inhibitors, as well as transcripts from toxins not detected in the venom that deserves further investigation. Human accident symptoms are well explained by the identified toxins, however, in its natural environment, little known and undescribed toxins must have specific and important role in predation. Identifying this diversity is important to better understand toxins ways of action.

Hemolysin toxin produced and secreted by pathogenic Escherichia coli is one of a family of cytolytic, structurally homologous protein toxins known as RTX (repeats in toxin) toxins. RTX toxins are products of a gene cluster, CABD . The A gene product, nontoxic hemolysin (proHlyA) is made toxic by post-translational fatty acylation of two internal lysine residues. HlyC, C gene product, is essential for acylation, and acyl-acyl carrier protein (ACP) is the acyl donor. HlyB and HlyD are involved in secretion of the toxin. HlyC was thought to serve as an internal protein acyltransferase and remained uncharacterized until now. ProHlyA and HlyC were separately subcloned, expressed, and purified, and acyl-ACPs with diverse radioactive acyl groups were synthesized. With these proteins, the conversion of proHlyA to HlyA by acyltransfer was assayed. Acyl-ACP was the obligate acyl donor. Acyltransfer was catalyzed by HlyC monomer, and an acyl-enzyme intermediate was detected and shown to catalyze the reverse reaction. The reaction mechanism was examined by steady state kinetics, and the nature of inhibitions by reaction products was determined. The kinetic mechanism of the internal protein acylation was compatible with an uni uni iso uni uni ping pong with isomerization of the F form of the enzyme. Clues to the chemical mechanism for the acyltransferase were elucidated by both chemical modification studies and site directed mutagenesis of the enzyme. Chemical modification experiments ruled out any critical cysteines, serines, and lysine residues, but suggested a role for histidine(s) and tyrosine(s) in acyltransferase function. In order to examine the function of specific residues and possibly corroborate the chemical findings, site directed mutagenesis studies of the acyltransferase were employed. Seventeen residues that were conserved among 13 different RTX toxin acyltransferases were individually mutated, and the respective HlyCs expressed, and characterized. Residues that were critical for acyltransferase function included Gly 11, His 23, Tyr 70, and Gly 85. As with chemical modification data, mutagenesis ruled out any conserved, essential, cysteines or serines critical for HlyC acyltransferase activity.

Pneumolysin, a protein toxin, represents one of the major virulence factors of Streptococcus pneumoniae. This pathogen causes bacterial meningitis with especially high disease rates in young children, elderly people and immunosuppressed patients. The protein toxin belongs to the family of cholesterol-dependent cytolysins, which require membrane cholesterol in order to bind and to be activated. Upon activation, monomers assemble in a circle and undergo conformational change. This conformational change leads to the formation of a pore, which eventually leads to cell lysis. This knowledge was obtained by studies that used a higher concentration compared to the concentration of pneumolysin found in the cerebrospinal fluid of meningitis patients. Thus, a much lower concentration of pneumolysin was used in this work in order to investigate effects of this toxin on primary mouse astrocytes. Previously, a small GTPase activation, possibly leading to cytoskeletal changes, was found in a human neuroblastoma cell line. This led to the hypothesis that pneumolysin can lead to similar cytoskeletal changes in primary cells. The aim of this work was to investigate and characterise the effects of pneumolysin on primary mouse astrocytes in terms of a possible pore formation, cellular trafficking and immunological responses. Firstly, the importance of pore-formation on cytoskeletal changes was to be investigated. In order to tackle this question, wild-type pneumolysin and two mutant variants were used. One variant was generated by exchanging one amino acid in the cholesterol recognising region, the second variant was generated by deleting two amino acids in a protein domain that is essential for oligomerisation. These variants should be incapable of forming a pore and were compared to the wild-type in terms of lytic capacities, membrane binding, membrane depolarisation, pore-formation in artificial membranes (planar lipid bilayer) and effects on the cytoskeleton. These investigations resulted in the finding that the pore-formation is required for inducing cell lysis, membrane depolarisation and cytoskeletal changes in astrocytes. The variants were not able to form a pore in planar lipid bilayer and did not cause cell lysis and membrane depolarisation. However, they bound to the cell membrane to the same extent as the wild-type toxin. Thus, the pore-formation, but not the membrane binding was the cause for these changes. Secondly, the effect of pneumolysin on cellular trafficking was investigated. Here, the variants showed no effect, but the wild-type led to an increase in overall endocytotic events and was itself internalised into the cell. In order to characterise a possible mechanism for internalisation, a GFP-tagged version of pneumolysin was used. Several fluorescence-labelled markers for different endocytotic pathways were used in a co-staining approach with pneumolysin. Furthermore, inhibitors for two key-players in classical endocytotic pathways, dynamin and myosin II, were used in order to investigate classical endocytotic pathways and their possible involvement in toxin internalisation. The second finding of this work is that pneumolysin is taken up into the cell via dynamin- and caveolin-independent pinocytosis, which could transfer the toxin to caveosomes. From there, the fate of the toxin remains unknown. Additionally, pneumolysin leads to an overall increase in endocytotic events. This observation led to the third aim of this work. If the toxin increases the overall rate of endocytosis, the question arises whether toxin internalisation favours bacterial tissue penetration of the host or whether it serves as a defence mechanism of the cell in order to degrade the protein. Thus, several proinflammatory cytokines were investigated, as previous studies describe an effect of pneumolysin on cytokine production. Surprisingly, only interleukin 6-production was increased after toxin-treatment and no effect of endocytotic inhibitors on the interleukin 6-production was observed. The conclusion from this finding is that pneumolysin leads to an increase of interleukin 6, which would not depend on the endocytotic uptake of pneumolysin. The production of interleukin 6 would enhance the production of acute phase proteins, T-cell activation, growth and differentiation. On the one hand, this activation could serve pathogen clearance from infected tissue. On the other hand, the production of interleukin 6 could promote a further penetration of pathogen into host tissue. This question should be further investigated. / Das Protein-Toxin Pneumolysin ist einer der entscheidenden Virulenzfaktoren von Streptococcus pneumoniae. Dieses Protein-Toxin gehört zur Familie der cholesterinabhängigen Zytolysine, die Membrancholesterol für ihre Aktivierung und Bindung benötigen. Nach der Membranbindung ordnen sich die Toxinmonomere kreisförmig an und ändern ihre Konformation, wodurch eine Pore entsteht, die dann zu einer Lyse der Zelle führt. Vor kurzem wurde nach Pneumolysinbehandlung in einer humanen Neuroblastomzelllinie eine Aktivierung kleiner GTPasen gefunden, die für zytoskelettale Veränderungen entscheidend sind (z.B. Zellbewegungen). Deshalb wurde die Hypothese aufgestellt, dass Pneumolysin diese zytoskelettalen Veränderungen auch in primären neuronalen Zellen auslösen könnte. Das Ziel dieser Arbeit war, die Effekte von Pneumolysin auf primäre Mausastrozyten im Hinblick auf Porenbildung, zelluläre Transportprozesse und immunologische Antworten zu untersuchen. Im ersten Teil wird die Bedeutung der Porenbildung auf zytoskelettale Veränderungen untersucht. Hierbei wurden lytische Fähigkeiten, Membranbindung, Membrandepolarisation, Porenbildung im künstlichen Bilayer und Effekte auf das Zytoskelett untersucht. Sowohl der Wildtyp als auch die Varianten zeigten die gleiche Stärke an Membranbindung. Diese Untersuchungen weisen darauf hin, dass die Porenbildung für die Zell-Lyse, Membrandepolarisation und zytoskelettale Veränderungen in Mausastrozyten wichtig ist und führt zu der Schlussfolgerung, dass nicht die Membranbindung, sondern die Porenbildung entscheidend für die beobachteten zytoskelettalen Veränderungen ist. Im zweiten Teil dieser Arbeit wurde der Effekt des Pneumolysin auf zelluläre Transportprozesse untersucht. Erneut zeigten die Pneumolysinvarianten keine Wirkung, während der Wildtyp die Gesamtrate der Endozytose erhöhte. Weiterhin wurde nur der Wildtyp internalisiert. Um einen möglichen Mechanismus für die Internalisierung des Toxins vorschlagen zu können, wurde Pneumolysin als GFP-markiertes Toxin genutzt. Weiterhin wurden einige Marker für unterschiedliche endozytotische Transportprozesse genutzt um eine Ko-lokalisation mit Pneumolysin-GFP zu ermöglichen. Des Weiteren wurden Inhibitoren für zwei Schlüsselproteine endozytotischer Vorgänge, Dynamin und Myosin II, genutzt. Die Ergebnisse dieser Untersuchungen zeigten, dass Pneumolysin wahrscheinlich durch dynamin- und caveolin-unabhängige Pinozytose in die Zelle aufgenommen wird. Dieser Mechanismus führt zu der Bildung von Caveosomen, deren weiterer Transport, und somit das Schicksal des internalisierten Toxins, bis heute noch nicht aufgeklärt ist. Die Beobachtung, dass Pneumolysin die Gesamtrate an Endozytose erhöht, führte zum dritten Teil dieser Arbeit. Wenn das Toxin die Gesamtrate an Endozytose erhöht, stellt sich die Frage, ob dieser Vorgang der Zerstörung des Toxins – also einer Abwehr der Zelle – dient, oder ob diese Internalisierung eine Strategie des Pathogens ist, um tiefer in das Wirtsgewebe einzudringen. Aktuelle Studien belegen, dass Pneumolysin einen Einfluss auf inflammatorische Antworten des Immunsystems hat. Aus diesem Grund wurden unterschiedliche proinflammatorische Zytokine untersucht. Überraschenderweise zeigte sich nur eine Erhöhung des Interleukin 6 nach der Toxinbehandlung. Weiterhin hatten die Endozytoseinhibitoren keinen Effekt auf die Produktion dieses proinflammatorischen Zytokins. Pneumolysin führt also zu einem Anstieg der Interleukin 6 Produktion, diese Produktion ist jedoch unabhängig von der Internalisierung dieses Toxins. Die Produktion dieses Interleukins würde zur Produktion der Akute-Phase Proteine, der Aktivierung der T-Zell Antwort, zu Wachstum und Zelldifferenzierung führen. Einerseits könnte diese Aktivierung die Infektion durch das Pathogen bekämpfen. Andererseits könnte S. pneumoniae die erhöhte Produktion durch PLY an Interleukin 6 nutzen um weiter in das Wirtsgewebe vordringen zu können. Diese Frage sollte noch durch weitere Experimente untersucht werden.

The ability to produce toxins is spread among a huge variety of bacterial strains. A very prominent class of bacterial protein toxins is the family of binary AB toxins sharing a common mode of intoxication. A pore forming component B binds and translocates an enzymatic component A into the cytosol of target cells exhibiting a fatal mode of action. These components are supposed to be not toxic themselves but both required for cell toxicity. Anthrax toxin produced by the Gram-positive bacteria Bacillus anthracis is the best studied binary toxin especially since its use as a biological weapon in the context of the attacks of 9/11 in 2001. In contrast to other binary toxins, Anthrax toxin possesses two different enzymatic components, edema factor (EF), a calcium- and calmodulin-dependent adenylat-cyclase and lethal factor (LF), a zinc-dependent metalloprotease. Protective antigen (PA) is the pore-forming component responsible for binding and translocation. Clostridium botulinum possesses in addition to the well known botulinum toxin (Botox) a variety of other toxins, such as the binary C2 toxin. C2 toxin is composed of the binding and translocation moiety C2II and the enzymatic moiety C2I acting as an actin-ADP-ribosyltransferase. In this study, the mode of translocation and the binding kinetics to the enzymatic component were studied in a biophysical experimental setup. In chapter 2, the binding of the N-terminal fractions EFN and LFN to the PA channel are analyzed in artificial bilayer membranes revealing lower binding affinity compared to full-length EF and LF. Other biophysical properties like voltage-dependency and ionic-strength dependency are not influenced. The results suggest that additional forces are involved in the binding process, than those concerning the N-terminus exclusively, as it was supposed previously. As the treatment of an Anthrax infection with antibiotics is often medicated very late due to the lack of early symptoms, tools to prevent intoxication are required. 4-aminoquinolones like chloroquine are known to block the PA channel, thereby inhibiting intoxication but they also lead to severe side-effects. In chapter 3 new promising agents are described that bind to PA in artificial bilayer systems, elucidating common motives and features which are necessary for binding to PA in general. The possible interaction of Anthrax and C2 toxin is investigated by measuring the binding of one enzymatic component to the respective other toxin’s pore (chapter 4). Interestingly, in vitro experiments using the black lipid bilayer assay show that PA is able to bind to C2I resulting in half saturation constants in the nanomolar range. Furthermore, in vivo this combination of toxin components exhibits cell toxicity in human cell lines. This is first-time evidence that a heterologous toxin combination is functional in in vitro and in vivo systems. In contrast, C2II is able to bind to EF as well as to LF in vitro, whereas in in vivo studies almost no toxic effect is detected. In the case of PA, an N-terminal His6-tag attached to the enzymatic subunit increased the binding affinity (chapter 5). A His6-tag attached to not related proteins also led to high binding affinities, providing the possibility to establish PA as a general cargo protein. In chapter 6 a set of different molecules and proteins is summarized, which are either related or not related to binary toxins, PA is able to bind. In first line, the presence of positive charges is found to be responsible for binding to PA which is in accordance to the fact that PA is highly cation selective. Furthermore, we present evidence that different cationic electrolytes serve as a binding partner to the PA channel. In the last decade another toxin has aroused public attention as it was found to be responsible for a rising number of nosocomial infections: Clostridium difficile CDT toxin. The mode of action of the enzymatic subunit CDTa is similar to C2I of C2 toxin, acting as an ADP-ribosylating toxin. The channel forming and binding properties of CDT toxin are studied in artificial bilayer membranes (chapter 7). We found that two different types of channels are formed by the B component CDTb. The first channel is similar to that of iota toxin’s Ib of Clostridium perfringens with comparable single channel conductance, selectivity and binding properties to the enzymatic subunit CDTa. The formation of this type of channel is cholesterol-dependent, whereas in the absence of cholesterol another kind of channel is observed. This channel has a single channel conductance which is rather high compared to all other binary toxin channels known so far, it is anion selective and does not show any binding affinity to the enzymatic component CDTa. The results reveal completely new insights in channel formation properties and the flexibility of a pore-forming component. Additionally, these findings suggest further possibilities of toxicity of the pore forming component itself which is not known for any other binary toxin yet. Therefore, the pathogenic role of this feature has to be studied in detail. / Die Fähigkeit, Toxine zu produzieren, ist unter verschiedensten Bakterienstämmen sehr verbreitet. Zu diesen Toxinen zählt auch die Familie der binären AB-Toxine, die hauptsächlich von Bakterien der Gattung Bacillus und Clostridium gebildet werden. Charakteristisch für diese bakteriellen Proteintoxine ist der Wirkungsmechanismus der Zellintoxikation. Eine porenformende Untereinheit B bindet eine enzymatische Untereinheit A und transportiert diese in das Zytosol von Zielzellen, die dort tödliche Wirkung entfalten. Es wird angenommen, dass die einzelnen Komponenten an sich nicht toxisch sind, sondern nur in Kombination Zellvergiftung auslösen. Anthrax-Toxin, das von dem Gram-positiven Bakterium Bacillus anthracis produziert wird, ist das bekannteste und am besten untersuchte binäre Toxin, besonders seit es im Jahr 2001 als Biowaffe eingesetzt wurde. Im Gegensatz zu anderen binären Toxinen besitzt das Anthrax-Toxin zwei enzymatische Komponenten: Edema Factor (EF), eine kalzium- und calmodulinabhängige Adenylatzyklase, und Lethal Factor (LF), eine zinkabhängige Metalloprotease. Protective Antigen (PA) ist die porenformende Komponente, die für die Binding und die Translokation der enzymatischen Untereinheiten verantwortlich ist. Clostridium botulinum produziert neben dem bekannten Botulinumtoxin (Botox) eine Reihe weiterer Toxine, unter anderem das binäre C2 Toxin. Dieses besteht aus der Binde- und Translokationskomponente C2II und der enzymatischen Komponente C2I, die als ADP-Ribosyltransferase fungiert. Im Rahmen der vorliegenden Arbeit werden der Translokationsmechanismus und die kinetischen Bindeeigenschaften dieser Toxine biophysikalisch untersucht. In Kapitel 2 wird die Bindung der N-terminalen Fragmente EFN und LFN an den PA-Kanal in künstlichen Lipidmembranen analysiert. Obwohl die Spannungs- und Ionenstärkeabhängigkeit unverändert sind, weisen die verkürzten Proteine deutlich geringe Bindeaffinitäten zu PA im Vergleich zu den vollständigen Proteinen auf. Die Ergebnisse zeigen, dass, anders als bisher angenommen, weitere Kräfte als die zwischen dem N-Terminus und dem PA-Kanal eine Rolle für die Bindung der enzymatischen Komponente spielen. Da bei einer Anthraxinfektion häufig keine frühen Symptome sichtbar sind, erfolgt die Behandlung mit Antibiotika in der Regel relativ spät. Daher werden neue Wirkstoffe benötigt, um einer Intoxikation vorzubeugen. Es ist bekannt, dass 4-Aminoquinolone, wie zum Beispiel Chloroquin, in der Lage sind, die PA-Pore zu blockieren und somit eine Zellvergiftung zu verhindern, allerdings haben diese Wirkstoffe starke Nebenwirkungen. In Kapitel 3 werden neue, vielversprechende Wirkstoffe beschrieben, die an PA binden können und Aufklärung darüber geben, welche Eigenschaften für die Bindung an PA im Allgemeinen verantwortlich sind. Des Weiteren wird untersucht, ob eine Kreuzreaktion zwischen den Komponenten des Anthrax- und C2-Toxins möglich ist (Kapitel 4). Dazu wird die Bindung einer enzymatischen Komponente an die Pore des entsprechenden anderen Toxins gemessen. Interessanterweise ergeben in vitro Experimente an künstlichen Lipidmembranen, dass PA an C2I bindet und in vivo Vergiftungen an humanen Zelllinien auslöst. Damit wird zum ersten Mal gezeigt, dass eine heterologe Toxinkombination sowohl in vitro als auch in vivo funktionell ist. C2II hingegen ist zwar in der Lage, EF und LF zu binden, die Transportrate in Zielzellen ist jedoch sehr gering. Im Fall von PA bewirkt ein N-terminaler His6-tag, der an die enzymtischen Einheiten gekoppelt ist, eine Erhöhung der Bindeaffinität, beschrieben in Kapitel 5. Dies ist sowohl für nah verwandte Proteine der Fall als auch für Proteine, die nicht im Zusammenhang mit binären Toxinen stehen. Somit eröffnet sich die Möglichkeit, PA als universelles Transportprotein zu nutzen. In Kapitel 6 werden verschiedene Moleküle und Proteine beschrieben, die in der Lage sind, an PA zu binden. Vor allem positive Ladungen scheinen für die Bindung an PA-Kanäle verantwortlich zu sein, was mit der Tatsache, dass PA stark kationenselektiv ist, im Einklang steht. Des Weiteren wird zum ersten Mal beschrieben, dass verschiedene Kationen selbst als Bindepartner fungieren können. Seit einigen Jahren ist ein weiteres Toxin in den Fokus der Öffentlichkeit gerückt, da es zunehmend für nosokomiale Infektionen verantwortlich gemacht wird: CDT-Toxin von Clostridium difficile. Wie das C2-Toxin besitzt CDT-Toxin ADP-Ribosyltransferaseaktivität, was zu irreversiblen Schäden des Aktin- Zytoskeletts und somit zum Zelltod führt. Die biophysikalischen Eigenschaften, betreffend Porenbildung und Bindeaffinität des CDT-Toxins werden in Kapitel 7 beschrieben. Wir zeigen, dass die B Komponente CDTb fähig ist, zwei unterschiedliche Kanäle zu bilden. Einer dieser Kanäle ist dem des Iota-Toxins von Clostridium perfringens ähnlich, die Einzelkanalleitfähigkeit, Selektivität und Bindeeigenschaften sind vergleichbar. Die Bildung dieses Kanals ist abhängig von Cholesterin, wohingegen in Abwesenheit von Cholesterin überwiegend ein anderer Kanal geformt wird. Dieser zeigt eine für einen binären Toxinkanal ungewöhnlich hohe Einzelkanalleitfähigkeit, der Kanal ist anionselektiv und weist keinerlei Bindeaffinität zu der enzymatischen Komponente CDTa auf. Die Ergebnisse offenbaren neue Einblicke in die Formierung von Toxinkanälen und deuten darauf hin, dass dieses Toxin durch die Flexibilität der Kanalbildung möglicherweise zusätzliche Fähigkeiten besitzt, Zellintoxikation auszulösen. Dennoch ist die physiologische und pathogene Rolle dieser Eigenschaft noch weitestgehend ungeklärt und bedarf intensiver Untersuchung.

Protective antigen component of B. anthracis toxin was produced and purified to the >99% level. Toxin was purified from culture supernatant utilizing concentration and liquid chromatography techniques. Purity was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified protective antigen retained biological and antigenic activity as evidenced respectively by lethality in Fischer 344 rats when injected in combination with lethal factor, and by positive results on the Ouchterlony double diffussion assay. Radioiodinated protective antigen was used both in the in vivo and the in vitro experiments. In vivo distribution of labelled protective antigen was determined in Fischer 344 rats. Assay of organ tissues for labelled protective antigen aided in the decision to use Maden-Darby bovine kidney cells for the cell cultures in the protective antigen binding studies. Protective antigen binding studies, all performed at 37°C, evaluated criteria for receptor existence. Labelled protective antigen was found to bind specifically and reversibly to Maden-Darby bovine kidney cells. Receptors proved to be saturable. Scatchard analysis showed a relatively high dissociation constant (KD= 17 X 10-9M) compared to other toxins in similar studies. This indicated moderately low affinity for protective antigen. The receptor was also partially characterized. It was shown that cholera toxin subunit B blocked the binding of labelled protective antigen to Maden-Darby bovine kidney cells and that the protective antigen receptor was insensitive to trypsin treatment. Both of these observations suggest a ganglioside as the receptor for protective antigen.

The Gram positive soil dwelling bacteria Bacillus subtilis produces spores when encountered with a low nutrient environment. However, B. subtilis can delay spore production by a mechanism known as cannibalism. Cannibalism is a process by which B. subtilis delays commitment to sporulation by killing a subpopulation of its cells. This process involves production of two toxins, SDP and SKF. SDP is a 42 amino acid peptide with a disulfide bond derived from the internal cleavage of its precursor protein pro-SdpC. pro-SdpC is part of the sdpABC operon. Production of extracellular SDP induces expression of the sdpRI operon. Encoded in this operon is the negative regulator SdpR and SdpI. SdpI is a dual function protein which acts both as a signal transduction protein and the immunity factor against SDP. The current model states that production of SDP is sensed via SdpI. SdpI will sequester SdpR to the membrane in response and allow for sdpRI expression. The aims of this dissertation are to establish the requirements for SDP production and its response via SdpI/SdpR during cannibalism. Studies in Chapter II were carried out to determine the factors required for production of the antimicrobial peptide SDP. Site directed mutagenesis of the leader signal peptide sequence in pro-SdpC demonstrated that proper signal peptide cleavage was required for SDP production. Additional site directed mutants of the cysteine residues in pro-SdpC revealed that these are not required for SDP toxic activity. These studies also included deletions within the sdpABC operon and revealed that the two proteins of unknown function, SdpA and SdpB are required for SDP production. Using mass spectrometry analysis, we found that SdpA and SdpB together are required to produce the active 42 amino acid peptide SDP. Taken together we concluded that SDP production was a multi step process which required proteins encoded within the operon and additional processing supplemented in the cell. In Chapter III we investigated the role of SdpI, specifically what residues were required for the signaling and immunity functions observed. Our initial screen, included site directed mutagenesis of highly conserved residues between the 4th and 5th transmembrane domains of SdpI. These resulted in over 20 SdpI mutants generated. From these, only two SdpI mutants had defects in either signal transduction or SDP immunity. Additional localized mutagenesis was used to isolate two other mutants in SdpI which only affected signal transduction or SDP immunity. SdpI signaling-immunity+ mutants presented a defect in SdpR membrane sequestration and sdpRIinduction. Our findings suggest these types of SdpI mutants may be important for the downstream effect of SdpR membrane sequestration. SdpI signaling+ immunity- mutants revealed defects in SDP protection. Some of the residues mutated were conserved in other SdpI homologs. Site directed mutagenesis of these conserved residues in the SdpI ortholog YfhL showed these are also required for SDP resistance. For the first time, we were able to identify mutations which affected only SDP immunity and gained further insight into how SdpI signaling-immunity+ mutants play a role during signal transduction. In Chapter IV we initiated studies to define what regions of the negative regulator SdpR are important for its function during cannibalism. We employed localized mutagenesis to identify SdpR mutants which decreased sdpRIexpression even in the presence of inducing signal. We isolated three such SdpR mutants, referred to as super repressors. We expect these SdpR super repressors are unable to be sequestered to the membrane in the presence of SDP.

Many plants and animals are defended by toxic compounds, and circumvention of those defenses often has involved the evolution of elaborate mechanisms for tolerance or resistance of the toxins. Toads synthesize potent cardiotonic steroids known as bufadienolides (BDs) from cholesterol and store those toxins in high concentrations in their cutaneous glands. Those toxins protect toads from the majority of predators, including most snakes that readily consume other species of frogs. BDs exert their effect by inhibiting ion transport by the Na+/K+-ATPase (NKA). This ubiquitous transmembrane enzyme consists of a catalytic alpha-subunit, which carries out the enzyme's functions, and a glycoprotein beta-subunit, which provides structural stability. Inhibition of the NKA causes highly elevated intracellular Ca2+ levels and results in often lethal increased cardiac contraction strength. Molecular resistance to bufadienolides in snakes is conferred by mutations in the alpha-subunit of the Na+/K+-ATPase. I have found that these mutations are more prevalent in snakes than previously suggested, and that many genetically resistant species do not feed on toads. This suggests that possession of the mutations alone does not carry substantial negative consequences, and that feeding on toads may have been an ancestral habit in some groups of snakes. I have further found evidence of tissue-specific variation in resistance to bufadienolides, and gene expression investigations revealed that the bufadienolide resistance-conferring mutations are not expressed equally among different organs. Variation in resistance among different tissues indicates that possession of the mutations does not protect all cells equally. Finally, by testing the physiological responses of resistant snakes to exposure to cardiotonic steroid, I have found that feeding on toads incurs negative consequences and that toad-specialized resistant snakes respond differently from nontoad-specialized resistant snakes. The presence of physiological consequences of toxin exposure may explain why feeding on toads has been lost in some lineages of snakes that retain resistance-conferring mutations. In summary, these findings indicate that genetic resistance of the Na+/K+-ATPase is necessary in order for snakes to survive acute toxicity of bufadienolides, but it is not sufficient to explain fully the physiological mechanisms involved in dealing with chronic exposure to the toxins.

Thesis (MOccTher.--Faculty of Health Sciences)-University of Pretoria, 2006. / Includes bibliographical references.

No description available.

Clostridium difficile is a leading cause of nosocomial infection in North America and a considerable challenge to healthcare professionals in hospitals and nursing homes. The Gram-positive bacterium produces two exotoxins, toxin A (TcdA) and toxin B (TcdB), which are the major virulence factors responsible for C. difficile-associated disease (CDAD) and are targets for CDAD therapy. In this work, recombinant single-domain antibody fragments (VHHs) which target the cell receptor binding domains of TcdA or TcdB were isolated from an immune, llama phage display library and characterized. Four VHHs (A4.2, A5.1, A20.1, and A26.8) were potent neutralizers of the cytopathic effects of TcdA in an in vitro assay and the neutralizing potency was enhanced when VHHs were administered in combinations. Epitope mapping experiments revealed that some synergistic combinations consisted of VHHs recognizing overlapping epitopes, an indication that factors other than mere epitope blocking are responsible for the increased neutralization. Binding assays revealed TcdA-specific VHHs neutralized TcdA by binding to sites other than the carbohydrate binding pocket of the toxin. The TcdB-specific VHHs failed to neutralize TcdB, as did a panel of human VL antibodies isolated from a synthetic library. To enhance the stability of the C. difficile TcdA-specific VHHs for oral therapeutic applications, the VHHs were expressed with an additional disulfide bond by introducing Ala/Gly54Cys and Ile78Cys mutations. The mutant VHHs were found to be well expressed, were non-aggregating monomers, retained low nM affinity for TcdA, and were capable of in vitro TcdA neutralization. Digestion of the VHHs with the major gastrointestinal proteases, at biologically relevant concentrations, revealed a significant increase in pepsin resistance for all mutants and an increase in chymotrypsin resistance for the majority of mutants without compromising inherent VHH trypsin resistance. Collectively, the second disulfide not only increased VHH thermal stability at neutral pH, as previously shown, but also represents a generic strategy to increase VHH stability at low pH and impart protease resistance. These are all desirable characteristics for the design of protein-based oral therapeutics. In conclusion, llama VHHs represent a class of novel, non-antibiotic inhibitors of infectious disease virulence factors such as C. difficile toxins.