Journal:Acta Cryst D:S2059798322001772

Crystal structure of the putative cell wall lipoglycan biosynthesis protein LmcA from Mycobacterium smegmatis

Onisha Patel, Rajini Brammananth, Weiwen Dai, Santosh Panjikar, Ross L. Coppel, Isabelle S. Lucet and Paul K. Crellin ^[1]

Molecular Tour
The bacterium Mycobacterium tuberculosis infects one-quarter of the entire human population, resulting in more than a million deaths from Tuberculosis each year. In their cell walls, Mycobacteria synthesize abundant, related cell wall glycolipids called phosphatidyl-myo-inositol mannosides (PIMs), lipomannans (LMs) and lipoarabinomannans (LAMs), which interact with the infected host. This paper describes the first crystal structure of LmcA, a recently identified Mycobacterial protein that converts PIMs into LMs and LAMs, via an unknown mechanism.

The LmcA structure revealed an elongated beta-barrel fold and one alpha-helix extending away from the beta-barrel core. Interestingly, two distinct cavities were found inside the protein which could bind a ligand. Further analysis revealed elements in LmcA that may undergo conformational changes to ‘open’ the protein, permitting access to the cavities. While the ligand remains to be identified, comparison of the crystal structure with LmcA models from other bacterial species suggests a common mechanism of ligand binding involving the cavities. These findings provide new structural insights into the biosynthetic pathway for PIM/LM/LAM, essential components of the mycobacterial cell surface.

References

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