Author: Lionel CladièrePublisher:
ISBN:
Category :
Languages : en
Pages : 288
Book Description
GTPases form a large family of proteins in the living world implicated in many fundamental cellular processes. My studies in this thesis have concerned the characterization of CpgA, a GTPase encoded by an essential gene (previously named, yloQ). The primary amino acid sequence of CpgA revealed the presence of G-motifs, typical of GTPases, however, unusually these are circularly permuted. The kinetic parameters of purified CpgA were determined and confirmed a specific but low GTPase activity. However, this activity is stimulated by the addition of ribosomes. Crystallization of CpgA permitted the determination of a high resolution structure at 1.6Å. The core structure of the GTPase domain is essentially identical to classical GTPases, despite the circular permutation. The structure of CpgA revealed two additional domains, an OB module and a zinc binding module which includes a novel metal coordinating site. In fact, this particular combination of modules with the G-domain is unique to bacteria. The structural features of CpgA, combined with recent detailed phylogeny analysis, is consistent with a role for CpgA in translation in protein synthesis. I have also shown using phase contrast microscopy, that an engineered reduction in the level of CpgA results in cells with abnormal morphology, in particular at low temperature. This phenotype was specifically corrected by re-introduction of a single copy of the cpgA gene. These results indicate that CpgA may be involved in the translation of subset of proteins, participating, for example, in the synthesis of the cell wall. The gene cpgA is localized downstream of two genes, prpC and prkC, encoding, respectively, a Ser/Thr protein phosphatase and a Ser/Thr protein kinase. The organization of this locus is conserved in several Gram positive bacteria, including some important pathogens. The products of these three genes could therefore play a role in the same signalling pathway.