MSc (Biochemistry) / Department of Biochemistry / Sustaining proteostasis is essential for the survival of the cell and altered protein regulation leads to many cellular pathologies. Heat shock proteins (Hsps) are involved in the regulation of the protein quality control. Hsps are a group of molecular chaperones that are upregulated in response to cell stress and some are produced constitutively. The Hsp70 family also known as DnaK in Escherichia coli (E. coli) is the most well-known group of molecular chaperones. Structurally, Hsp70s consist of a nucleotide binding domain (NBD) and a substrate binding domain (SBD) conjugated by a linker sub-domain. ATP binding and hydrolysis is central to the Hsp70 functional cycle. Hsp70s play a role in cytoprotection especially during heat stress in E. coli. Hsp70s from different organisms are thought to exhibit specialized cellular functions. As such E. coli Hsp70 (DnaK) is a molecular chaperone that is central to proteostasis in E. coli. On the other hand, Plasmodium falciparum Hsp70s are structurally amenable to facilitate folding of P. falciparum substrates. The heterologous production of P. falciparum proteins in E. coli towards drug discovery has been a challenge. There is need to develop tools that enhance heterologous expression and proper folding of P. falciparum proteins in an E. coli expression system. To this end, a chimeric Hsp70, KPf consisting of E. coli DnaK NBD and P. falciparum Hsp70-1 (PfHsp70-1) SBD was previously designed. KPf was shown to confer cytoprotection to E. coli DnaK deficient cells that were subjected to heat stress. In this study it was proposed that KPf has an advantage over E. coli DnaK and PfHsp70-1 in its function as a protein folding chaperone. Therefore, the main aim of this study was to characterize the chaperone function of KPf relative to the function of wild type E. coli and P. falciparum Hsp70s. The recombinant forms of KPf, DnaK and PfHsp70-1 proteins were successfully expressed and purified using nickel affinity chromatography. Circular Dichroism (CD) structural study demonstrated that KPf and PfHsp70-1 are predominantly α-helical and are also heat stable. Tertiary structure studies of PfHsp70-1 and KPf using tryptophan fluorescence revealed that both confirmations of recombinant proteins are perturbed by the presence of ATP more than ADP. Interestingly, the substrate binding capabilities of these proteins were comparable both in the absence or presence of nucleotides ATP/ADP. KPf is an independent chaperone, that exhibit nucleotide binding and hydrolysis. The current study has established unique structure-function features of KPf that distinguishes it from its “parental” forms, DnaK and PfHsp70-1. / NRF

Background: Heat-shock proteins of the 70 kDa family (Hsp70s) are essential chaperones required for key cellular functions. In eukaryotes, four subfamilies can be distinguished according to their function and localisation in different cellular compartments: cytosol, endoplasmic reticulum, mitochondria and chloroplasts. Generally, multiple cytosol-type Hsp70s can be found in metazoans that show either constitutive expression and/or stress-inducibility, arguing for the evolution of different tasks and functions. Information about the hsp70 copy number and diversity in microbial eukaryotes is, however, scarce, and detailed knowledge about the differential gene expression in most protists is lacking. Therefore, we have characterised the Hsp70 gene family of Paramecium caudatum to gain insight into the evolution and differential heat stress response of the distinct family members in protists and to investigate the diversification of eukaryotic hsp70s focusing on the evolution of heat-inducibility. Results: Eleven putative hsp70 genes could be detected in P. caudatum comprising homologs of three major Hsp70-subfamilies. Phylogenetic analyses revealed five evolutionarily distinct Hsp70-groups, each with a closer relationship to orthologous sequences of Paramecium tetraurelia than to another P. caudatum Hsp70-group. These highly diverse, paralogous groups resulted from duplications preceding Paramecium speciation, underwent divergent evolution and were subject to purifying selection. Heat-shock treatments were performed to test for differential expression patterns among the five Hsp70-groups as well as for a functional conservation within Paramecium. These treatments induced exceptionally high mRNA up-regulations in one cytosolic group with a low basal expression, indicative for the major heat inducible hsp70s. All other groups showed comparatively high basal expression levels and moderate heat-inducibility, signifying constitutively expressed genes. Comparative EST analyses for P. tetraurelia hsp70s unveiled a corresponding expression pattern, which supports a functionally conserved evolution of the Hsp70 gene family in Paramecium. Conclusions: Our analyses suggest an independent evolution of the heat-inducible cytosol-type hsp70s in Paramecium and in its close relative Tetrahymena, as well as within higher eukaryotes. This result indicates convergent evolution during hsp70 subfunctionalization and implies that heat-inducibility evolved several times during the course of eukaryotic evolution.

Background: Heat-shock proteins of the 70 kDa family (Hsp70s) are essential chaperones required for key cellular functions. In eukaryotes, four subfamilies can be distinguished according to their function and localisation in different cellular compartments: cytosol, endoplasmic reticulum, mitochondria and chloroplasts. Generally, multiple cytosol-type Hsp70s can be found in metazoans that show either constitutive expression and/or stress-inducibility, arguing for the evolution of different tasks and functions. Information about the hsp70 copy number and diversity in microbial eukaryotes is, however, scarce, and detailed knowledge about the differential gene expression in most protists is lacking. Therefore, we have characterised the Hsp70 gene family of Paramecium caudatum to gain insight into the evolution and differential heat stress response of the distinct family members in protists and to investigate the diversification of eukaryotic hsp70s focusing on the evolution of heat-inducibility. Results: Eleven putative hsp70 genes could be detected in P. caudatum comprising homologs of three major Hsp70-subfamilies. Phylogenetic analyses revealed five evolutionarily distinct Hsp70-groups, each with a closer relationship to orthologous sequences of Paramecium tetraurelia than to another P. caudatum Hsp70-group. These highly diverse, paralogous groups resulted from duplications preceding Paramecium speciation, underwent divergent evolution and were subject to purifying selection. Heat-shock treatments were performed to test for differential expression patterns among the five Hsp70-groups as well as for a functional conservation within Paramecium. These treatments induced exceptionally high mRNA up-regulations in one cytosolic group with a low basal expression, indicative for the major heat inducible hsp70s. All other groups showed comparatively high basal expression levels and moderate heat-inducibility, signifying constitutively expressed genes. Comparative EST analyses for P. tetraurelia hsp70s unveiled a corresponding expression pattern, which supports a functionally conserved evolution of the Hsp70 gene family in Paramecium. Conclusions: Our analyses suggest an independent evolution of the heat-inducible cytosol-type hsp70s in Paramecium and in its close relative Tetrahymena, as well as within higher eukaryotes. This result indicates convergent evolution during hsp70 subfunctionalization and implies that heat-inducibility evolved several times during the course of eukaryotic evolution.

En 1977, Carl Woese sépare les procaryotes en deux grands groupes en proposant une nouvelle classification basée sur des critères phylogénétiques. Les Archaea deviennent ainsi un domaine à part entière aux cotés des Bacteria et des Eucarya. Depuis, la compréhension de ce nouveau groupe et de ses relations avec les deux autres domaines, essentielles pour comprendre l'évolution ancienne du vivant, est largement passée par l'étude de leur phylogénie. Presque 40 ans de recherche sur les archées ont permis de faire évoluer leur image : de bactéries vivant dans des milieux spécialisés, souvent extrêmes, on est passé à un domaine indépendant, très diversifié aussi bien génétiquement, métaboliquement ou encore écologiquement. Ces dernières années la barre symbolique de cent génomes complets d'archées séquencés a été franchie et, parallèlement, les projets génomiques et métagénomiques sur des groupes peu caractérisés ou de nouvelles lignées de haut rang taxonomique (e.g. Nanohaloarchaea, Thaumarchaeota, ARMAN, Aigarchaeota, groupe MGC, groupe II des Euryarchaeota, etc.) se sont multipliés. Tout ceci apporte un matériel sans précédent pour l'étude de l'histoire évolutive et de la diversité des Archaea. Les protéines ribosomiques ont été utilisées de façon courante pour inférer la position phylogénétique des nouvelles lignées d'Archaea. Néanmoins, les phylogénies résultantes ne sont pas complètement résolues, laissant des interrogations concernant d'importantes relations de parenté. La recherche de nouveaux marqueurs est donc cruciale et c'est dans ce contexte que mon projet de thèse s'inscrit. À partir de l'analyse des génomes de deux Thaumarchaeota et d'une Aigarchaeota, nous avons identifié 200 protéines conservées et bien représentées dans les différents phyla d'archées. Ces protéines sont impliquées dans de nombreux processus cellulaires, ce qui peut apporter un signal phylogénétique complémentaire à celui des marqueurs de type informationnel utilisés par le passé. En plus de confirmer la plupart des relations phylogénétiques inférées à partir de ces derniers (i.e., protéines ribosomiques et sous unités de l'ARN polymérase), l'analyse phylogénétique de ces nouveaux marqueurs apporte un signal permettant une meilleure résolution de la phylogénie des archées et la clarification de certaines relations jusqu'ici confuses. Un certain nombre de ces nouveaux marqueurs sont aussi présents chez les bactéries. Les relations entre les grands phyla d'archées restant encore non résolues, nous avons utilisé ces protéines pour essayer de placer la racine de l'arbre des Archaea en utilisant comme groupe extérieur les bactéries. Nous avons ainsi pu identifier 38 protéines, parmi les 200 sélectionnées précédemment, ayant un signal phylogénétique suffisamment fiable pour cette étude, auxquelles nous avons ajouté 32 protéines ribosomiques universelles. L'utilisation conjointe de ces données nous a permis de placer la racine entre les Euryarchaeota, d'une part, et un groupe rassemblant les Thaumarchaeota, les Aigarchaeota, les Korarchaeota et les Crenarchaeota, d'autre part. Ce nouvel éclairage sur l'évolution ancienne des archées nous a amené à proposer une révision de leur taxonomie avec, principalement, la création du nouveau phylum "Proteoarchaeota" contenant les quatre phyla actuels que nous proposons de rétrograder en classes : Thaumarchaea, Aigarchaea, Korarchaea et Crenarchaea.Finalement, l'analyse des protéines codées dans les trois génomes qui ont servi de point de départ de ma thèse nous a permis de générer une masse considérable de données qui ont révélé des traits particuliers ou encore des histoires évolutives inattendues. Un exemple est l'histoire du complexe formé par la chaperonne DnaK et de ses co-chaperonnes GrpE, DnaJ, et DnaJ-Fer chez les Thaumarchaeota, impliquant plusieurs transferts horizontaux entre les trois domaines du vivant.

The antimicrobial peptide (AMP) ARV-1502 was designed based on naturally occurring short proline-rich AMPs, including pyrrhocoricin and drosocin. Identification of chaperone DnaK as a therapeutic target in Escherichia coli triggered intense research on the ligand- DnaK-interactions using fluorescence polarization and X-ray crystallography to reveal the binding motif and characterize the influence of the chaperone on protein refolding activity, especially in stress situations. In continuation of this research, 182 analogs of ARV-1502 were designed by substituting residues involved in antimicrobial activity against Gramnegative pathogens. The peptides synthesized on solid-phase were examined for their binding to E. coli and S. aureus DnaK providing 15 analogs with improved binding characteristics for at least one DnaK. These 15 analogs were distinguished from the original sequence by their increased hydrophobicity parameters. Additionally, the influence of the entire DnaK chaperone system, including co-chaperones DnaJ and GrpE on refolding and ATPase activity, was investigated. The increasingly hydrophobic peptides showed a stronger inhibitory effect on the refolding activity of E. coli chaperones, reducing protein refolding by up to 64%. However, these more hydrophobic peptides had only a minor effect on the ATPase activity. The most dramatic changes on the ATPase activity involved peptides with aspartate substitutions. Interestingly, these peptides resulted in a 59% reduction of the ATPase activity in the E. coli chaperone system whereas they stimulated the ATPase activity in the S. aureus system up to 220%. Of particular note is the improvement of the antimicrobial activity against S. aureus from originally >128 μg/mL to as low as 16 μg/mL. Only a single analog exhibited improved activity over the original value of 8 μg/mL against E. coli. Overall, the various moderate-throughput screenings established here allowed identifying (un)favored substitutions on 1) DnaK binding, 2) the ATPase activity of DnaK, 3) the refolding activity of DnaK alone or together with co-chaperones, and 4) the antimicrobial activity against both E. coli and S. aureus.