Résumé
The mycobacterial genus, which includes M. tuberculosis, the etiologic agent of tuberculosis, and nontuberculousmycobacteria (NTM) such as M. abscessus, represents a major threat to Human health.One challenge in the design of new therapies lies in the presence of a highly complex and hydrophobicouter membrane, known as the mycomembrane, which contains unique surface-exposed trehalosebasedglycolipids that are important for the survival and virulence of the bacteria. Of interest, theseglycolipids are synthesized in the cytoplasm and transported across the plasma membrane by integralmembrane proteins called MmpLs, that appear to be substrate specific to each glycolipid exported [1].Our preliminary results based on the AlphaFold 3D structure prediction of the 31 MmpLs from M.abscessus, the species that possesses the highest number of different MmpLs, suggested a possibleclassification of these transporters into two groups, based on the presence or absence of an extensionin their periplasmic domain. In this context, we propose a model in which the MmpLs possessing this“coiled-coil”-like extension may homotrimerize to form a channel large enough to transport theirsubstrate, and long enough to span the inner and outer membranes (Fig. 1). To test this hypothesis,we expressed and purified MmpL10 from M. smegmatis, the transporter of the diacyl trehalose (DAT)precursors of trehalose polyphleates, and which possesses this periplasmic extension. Remarkably,the full-length MmpL10 revealed a 3-fold increase of its molecular weight, as compared with thetruncated form lacking the “coiled-coil” motif in solution, when assessed by size-exclusionchromatography. These findings support our hypothesis that the periplasmic extension plays a criticalrole in the oligomerization of the MmpL10-like proteins, shedding light on a previously unknownmechanism of MmpL-driven glycolipid transport in mycobacteria. To further validate these obtainedresults, we are planning on characterizing the structure of MmpL10 using single-particle cryo-EM