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Mol Microbiol. 2016 Mar;99(5):866-83. doi: 10.1111/mmi.13283. Epub 2015 Dec 18.

Insights into the smooth-to-rough transitioning in Mycobacterium bolletii unravels a functional Tyr residue conserved in all mycobacterial MmpL family members.

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Centre National de la Recherche Scientifique FRE3689, Centre d'études d'agents Pathogènes et Biotechnologies pour la Santé, Université de Montpellier, 1919 route de Mende, 34293, Montpellier, France.
Centre d'Immunologie de Marseille-Luminy, Aix-Marseille Université UM2, Inserm, U1104, CNRS UMR7280, 13288, Marseille, France.
UMR1173, INSERM, Université de Versailles St Quentin, 2 avenue de la Source de la Bièvre, 78180, Montigny le Bretonneux, France.
Institut Pasteur, PF1 Génopole, 28 rue du Dr. Roux, 75724, Paris, France.
Institut Pasteur, Unité de Pathogénomique Mycobactérienne Intégrée, 25 rue du Dr. Roux, 75724, Paris, France.
INSERM, CPBS, 34293, Montpellier, France.


In mycobacteria, MmpL proteins represent key components that participate in the biosynthesis of the complex cell envelope. Whole genome analysis of a spontaneous rough morphotype variant of Mycobacterium abscessus subsp. bolletii identified a conserved tyrosine that is crucial for the function of MmpL family proteins. Isogenic smooth (S) and rough (R) variants differed by a single mutation linked to a Y842H substitution in MmpL4a. This mutation caused a deficiency in glycopeptidolipid production/transport in the R variant and a gain in the capacity to produce cords in vitro. In zebrafish, increased virulence of the M. bolletii R variant over the parental S strain was found, involving massive production of serpentine cords, abscess formation and rapid larval death. Importantly, this finding allowed us to demonstrate an essential role of Tyr842 in several different MmpL proteins, including Mycobacterium tuberculosis MmpL3. Structural homology models of MmpL4a and MmpL3 identified two additional critical residues located in the transmembrane regions TM10 and TM4 that are facing each other. We propose that these central residues are part of the proton-motive force that supplies the energy for substrate transport. Hence, we provide important insights into mechanistic/structural aspects of MmpL proteins as lipid transporters and virulence determinants in mycobacteria.

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