Conférences de la Pre Daniela Quaglia et du Pr Rong Shi

Conférence de la professeure Daniela Quaglia

« Engineering campaign on a lipase enabled the alteration of substrate selectivity while revealing hard-to-predict epistatic interactions. »

Résumé :

CalA is a versatile biocatalyst that, even though less studied than famous CalB, presents a unique combination of features (high temperatures and acidic pH stability, and the ability to accept bulky substrates) that make it an ideal target for development into an industrial lipase. An engineering campaign of the enzyme was carried out to improve its selectivity towards the hydrolysis of fatty acid esters of different chain lengths: a sought-for quality in industry for fatty acid enrichment. While allowing for the desired selectivity, our mutational efforts unlocked a deeper understanding of the mode of action of the enzyme. We confirmed the existence of a tunnel region fundamental for substrate recognition, and, unexpectedly, we discovered that other residues in distal regions are also key for modulating substrate selectivity, giving rise to a much more complex mechanism than expected and shedding light on epistatic interactions.

Conférence du professeur Rong Shi

«Structural and functional study of the putative acetylcholinesterase ChoE from Pseudomonas aeruginosa ».

Résumé :

Unlike the well-studied mammalian acetylcholinesterases (AChEs), much less is known about the structure and molecular mechanism of prokaryotic acetylcholinesterases. In our investigation of ChoE, a putative bacterial acetylcholinesterase from Pseudomonas aeruginosa, we found that ChoE is indispensable for P. aeruginosa growth when acetylcholine serves as the sole carbon and nitrogen source. ChoE adopts a typical fold of the SGNH hydrolase family and features a D285-H288-S38 catalytic triad. Its overall structure shows no similarity to that of eukaryotic AChEs indicating convergent evolution. Multiple crystal structures of ChoE reveal the molecular basis of substrate recognition, catalysis, and substrate inhibition, establishing ChoE as a prototype for other prokaryotic acetylcholinesterases. Futhermore, trapping of acyl-enzyme intermediates via different ChoE mutants, along with analysis of related structures, suggests the rate-limiting step of hydrolysis likely occurs during deacylation. Ser38, which switchs between three alternate conformations, regulates the Ser-Asn geometry in the active site and controls the functional state of ChoE: substrate binding and catalysis (active mode), product binding (substrate inhibition mode), or product release (clearing/purging mode). Importantly, our structural analysis of other SGNH enzymes further supports the functional role of the Ser conformational plasticity in SGNH hydrolases.