Conférence – Dr. Charles Calmettes, vendredi le 12 juillet à 11h00

PROTEO a le plaisir de vous inviter vendredi le 12 juillet à 11h00 à la présentation du Dr. Charles Calmettes (Institut national de la recherche scientifique) invité par le Dre. Daniela Quaglia (Université du Québec à Montréal) dans le pavillon de Chimie et Biochimie, salle CB-R450 – Université du Québec à Montréal.

“ Structural insights into bacterial outer membrane biogenesis – investigation of the TamA insertase promoting outer membrane protein assembly”

The outer membrane (OM) of Gram-negative bacteria serves as a vital organelle that is densely populated with outer membrane proteins (OMPs) and plays pivotal roles in cellular functions and virulence. The assembly and insertion of these OMPs into the OM represents a fundamental process requiring specialized molecular chaperones. One example is the translocation and assembly module (TAM), which functions as a transenvelope chaperone promoting the folding of specific autotransporters, adhesins, and secretion systems. The catalytic unit of TAM, TamA, comprises a catalytic β-barrel domain anchored within the OM and three periplasmic POTRA domains that recruit the TamB subunit. The latter acts as a periplasmic ladder that facilitates the transport of unfolded OMPs across the periplasm. Previously presumed to have no involvement in the assembly process, the POTRA domains were revealed in our laboratory to interact with the inner surface of the OM, ultimately modulating the membrane properties. Through the integration of X-ray crystallography, molecular dynamic simulations, and biomolecular interaction methodologies, we located the membrane-binding site on the first and second POTRA domains. Our investigation highlights a binding preference for phosphatidylglycerol, a minor lipid constituent present in the OM, which has been previously reported to facilitate OMP assembly. In the context of the densely OMP-populated membrane, we hypothesize that the POTRA-membrane interaction serves as a mechanism to secure lipid accessibility for nascent OMPs through steric interactions with existing OMPs, in addition to creating favorable conditions for OMP biogenesis.

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