Les thioltransférases, des agents doubles impliqués dans le métabolisme du sulfure d’hydrogène : de la catalyse aux rôles physiologiques

Abstract : 3-mercaptopyruvate sulfurtransferases (3-MSTs) and thiosulfate sulfurtransferases (TSTs) are ubiquitous enzymes that belong to the rhodanese sulfurtransferase family and catalyze the transfer of a sulfur atom from a donor to an acceptor substrate via a cysteine-persulfide intermediate. While 3-MSTs are involved in the biogenesis of hydrogen sulfide (H2S), a gasotransmitter known to be toxic at high concentration, TSTs are likely responsible of its degradation. My project mainly focused on deciphering the sulfurtransferase-dependent molecular mechanisms to better define their physiological functions. To address these questions, their catalytic mechanisms and substrate specificities were investigated. This was achieved through the development of kinetic approaches (fluorescence, stopped-flow, H2S specific probe) to study each step of the reaction catalyzed by human (3-MST, TSTD1 and Rhodanese) and Escherichia coli (3-MST, GlpE) enzymes and structure-function relationship studies performed in collaboration for the theoretical chemistry and the X-ray crystallography parts. Here, I show that the active site of these enzymes is optimized to perform an efficient S0 transfer from non-activated sulfur compounds. Moreover, the mechanisms leading to formation of the persulfide intermediate do not depend on the enzyme but rather on the donor substrate. Indeed, the cleavage of the carbon-sulfur bond of 3-mercaptopyruvate critically depends on the CysX5 catalytic loop acting as a thiolate hole to favor the deprotonation of the essential Cys and the substrate, and on a water-mediated protonation step. In the presence of thiosulfate, the Cys activation mode remains unchanged and the reaction of sulfur transfer is only driven by the neutralization of the negative charges of the substrate. In addition, we propose a new physiological function for the human 3-MST in the cytoplasmic elimination of sulfite, a toxic compound for the cells. Finally, the two human mitochondrial TSTs are likely to be involved in the H2S-mediated cellular signaling, through the formation of polysulfide entities, but also in H2S catabolism
Document type :
Theses
Complete list of metadatas

https://hal.univ-lorraine.fr/tel-01934624
Contributor : Thèses Ul <>
Submitted on : Monday, November 26, 2018 - 10:02:23 AM
Last modification on : Tuesday, November 27, 2018 - 1:22:21 AM

Identifiers

  • HAL Id : tel-01934624, version 1

Collections

Citation

Jean-Christophe Lec. Les thioltransférases, des agents doubles impliqués dans le métabolisme du sulfure d’hydrogène : de la catalyse aux rôles physiologiques. Biochimie, Biologie Moléculaire. Université de Lorraine, 2017. Français. ⟨NNT : 2017LORR0305⟩. ⟨tel-01934624⟩

Share

Metrics

Record views

13