Identification of an α(1→6) mannopyranosyltransferase (MptA), involved in Corynebacterium glutamicum lipomanann biosynthesis, and identification of its orthologue in Mycobacterium tuberculosis

Corynebacterium glutamicum and Mycobacterium tuberculosis share a similar cell wall architecture, and the availability of their genome sequences has enabled the utilization of C. glutamicum as a model for the identification and study of, otherwise essential, mycobacterial genes involved in lipomannan (LM) and lipoarabinomannan (LAM) biosynthesis. We selected the putative glycosyltransferase‐Rv2174 from M. tuberculosis and deleted its orthologue NCgl2093 from C. glutamicum. This resulted in the formation of a novel truncated lipomannan (Cg‐t‐LM) and a complete ablation of LM/LAM biosynthesis. Purification and characterization of Cg‐t‐LM revealed an overall decrease in molecular mass, a reduction of α(1→6) and α(1→2) glycosidic linkages illustrating a reduced degree of branching compared with wild‐type LM. The deletion mutant's biochemical phenotype was fully complemented by either NCgl2093 or Rv2174. Furthermore, the use of a synthetic neoglycolipid acceptor in an in vitro cell‐free assay utilizing the sugar donor β‐d‐mannopyranosyl‐1‐monophosphoryl‐decaprenol together with the neoglycolipid acceptor α‐d‐Manp‐(1→6)‐α‐d‐Manp‐O‐C8 as a substrate, confirmed NCgl2093 and Rv2174 as an α(1→6) mannopyranosyltransferase (MptA), involved in the latter stages of the biosynthesis of the α(1→6) mannan core of LM. Altogether, these studies have identified a new mannosyltransferase, MptA, and they shed further light on the biosynthesis of LM/LAM in Corynebacterianeae.