A NAD-dependent Glutamate dehydrogenase coordinates metabolism with cell division in Caulobacter crescentus

Thèse de l'étudiant: Doc typesDocteur en Sciences

Résumé

Cell division is a key process to ensure survival, development and spreading of all livings. Cell division must be coordinated with other cellular processes such as chromosome replication or growth but also according to nutrient supplies i.e. metabolism. How bacteria control cytokinesis in function of metabolic availability remains poorly understood. In bacteria, the earliest event of cell division is the positioning of the tubulin-like GTPase FtsZ at the future site of division. There, FtsZ assembles into a polymeric and dynamic structure, the Z-ring thanks to GTP binding and lateral interaction between FtsZ filaments. At the division site, the Z-ring served as a scaffold for all of the cell division proteins and has been proposed to drive the constriction process. Due to its central role in cytokinesis, FtsZ is a prime target for the regulation of cell division. Here, we identified a NAD(H)-dependent glutamate dehydrogenase (GDH) that controls Z-ring disassembly coupling cell division with cellular growth in the α–proteobacterium Caulobacter crescentus. GDH catalyzes the interconversion of glutamate into NH4+ and α-ketoglutarate, thereby linking nitrogen and Krebs cycles. We found that GdhZ (for glutamate dehydrogenase interacting with FtsZ) directly stimulates the GTPase activity of FtsZ in vitro, leading to protofilaments shrinkage, only when GdhZ was enzymatically active. Absence of GdhZ strongly delays cytokinesis in C. crescentus and leads to various cell division defects. GdhZ co-localizes with FtsZ in late predivisional cells and GdhZ abundance varies during the cell cycle being specifically degraded during DNA replication the period during which the Z-ring is assembled at the division site in C. crescentus. Altogether these results prompt us to propose a model where GdhZ stimulates Z-ring disassembly in predivisional cells allowing daughter cells release with sufficient nutrient supplies to ensure survival. The high observed Km of GdhZ for glutamate suggests that active GdhZ could provide a plenty signal to the division apparatus. Interestingly, deletion of gdhZ homolog in the facultative intracellular pathogen Brucella abortus (gdhZba) leads to cell division defects, similarly to Caulobacter ∆gdhZ. Moreover, it impairs proper intracellular replication of Brucella during infection of macrophages, strongly suggesting that the catabolic activity of GdhZba is required for a successful infection. In addition, we found that during cytokinesis GdhZ activity is coordinated with the cell division regulator KidO. KidO is a putative oxidoreductase whose cell division control relies on its NAD(H)-binding ability. We showed that, in vitro, KidO inhibits lateral interactions between FtsZ-protofilaments (bundles) only in presence of NADH. Interestingly GdhZ and KidO are similarly regulated along the cell cycle of C. crescentus. In vitro, addition of KidO enhances GdhZ stimulatory effect on the GTPase activity of FtsZ, which lead us to propose that GdhZ and KidO act synergistically to stimulate depolymerization of the Z-ring, KidO dissociating FtsZ bundles and GdhZ stimulating GTPase activity of newly available FtsZ protofilaments. Altogether this work illustrates how C. crescentus can adjust cell cycle parameters according to nutrient availability fluctuations.

In addition, we found that GdhZ activity is coordinated with the cell division regulator KidO during cytokinesis. KidO is a putative oxido-reductase controlling cell division only when bound to NAD(H). We show that, in vitro, KidO inhibits lateral interactions between FtsZ-protofilaments (bundles) only in the presence of NADH but not NAD+. Interestingly GdhZ and KidO are similarly regulated along the cell cycle of C. crescentus. In vitro, addition of KidO enhances GdhZ stimulatory effect on the GTPase activity of FtsZ, which lead us to propose that GdhZ and KidO act synergistically to stimulate depolymerization of the Z-ring. In our model, KidO dissociates FtsZ bundles and GdhZ stimulates GTPase activity of newly available FtsZ protofilaments.

Altogether this work illustrates how bacteria can adjust cell cycle parameters according to nutrient availability fluctuations.
la date de réponse7 nov. 2014
langue originaleAnglais
L'institution diplômante
  • Universite de Namur
SuperviseurRegis Hallez (Promoteur), Xavier De Bolle (Copromoteur), Patricia Renard (Président), Patrick VIOLLIER (Jury), Leendert HAMOEN (Jury) & Bernard Hallet (Jury)

Contient cette citation

A NAD-dependent Glutamate dehydrogenase coordinates metabolism with cell division in Caulobacter crescentus
Beaufay, F. (Auteur). 7 nov. 2014

Thèse de l'étudiant: Doc typesDocteur en Sciences