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Publication Abstract from PubMed

The bacterial genus Mycobacterium includes important pathogens, most notably M. tuberculosis, which infects one-quarter of the entire human population, resulting in around 1.4 million deaths from tuberculosis each year. Mycobacteria, and the closely related corynebacteria, synthesize a class of abundant glycolipids, the phosphatidyl-myo-inositol mannosides (PIMs). PIMs serve as membrane anchors for hyperglycosylated species, lipomannan (LM) and lipoarabinomannan (LAM), which are surface-exposed and modulate the host immune response. Previously, in studies using the model species Corynebacterium glutamicum, NCgl2760 was identified as a novel membrane protein that is required for the synthesis of full-length LM and LAM. Here, the first crystal structure of its ortholog in Mycobacterium smegmatis, MSMEG_0317, is reported at 1.8 A resolution. The structure revealed an elongated beta-barrel fold enclosing two distinct cavities and one alpha-helix extending away from the beta-barrel core, resembling a `cone with a flake' arrangement. Through xenon derivatization and structural comparison with AlphaFold2-derived predictions of the M. tuberculosis homolog Rv0227c, structural elements were identified that may undergo conformational changes to switch from `closed' to `open' conformations, allowing cavity access. An AlphaFold2-derived NCgl2760 model predicted a smaller beta-barrel core with an enclosed central cavity, suggesting that all three proteins, which were collectively termed LmcA, may have a common mechanism of ligand binding through these cavities. These findings provide new structural insights into the biosynthetic pathway for a family of surface lipoglycans with important roles in mycobacterial pathogenesis.

Crystal structure of the putative cell-wall lipoglycan biosynthesis protein LmcA from Mycobacterium smegmatis.,Patel O, Brammananth R, Dai W, Panjikar S, Coppel RL, Lucet IS, Crellin PK Acta Crystallogr D Struct Biol. 2022 Apr 1;78(Pt 4):494-508. doi:, 10.1107/S2059798322001772. Epub 2022 Mar 11. PMID:35362472^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.