Novel lipoarabinomannan-like lipoglycan (CdiLAM) contributes to the adherence of Corynebacterium diphtheriae to epithelial cells.

The genus Corynebacterium is part of the phylogenetic group nocardioform actinomycetes. Members of this group have a characteristic cell envelope structure composed primarily of branched long-chain lipids, termed mycolic acids, and a rich number of lipoglycans such as lipoarabinomanans (LAM) and lipomannans. In this study, we identified a novel LAM variant isolated from Corynebacterium diphtheriae named CdiLAM. The key structural features of CdiLAM are a linear alpha-1-->6-mannan with side chains containing 2-linked alpha-D-Manp and 4-linked alpha-D-Araf residues. The polysaccharide backbone is linked to a phosphatidylinositol anchor. In contrast to the LAMs of other members of actinomycetales, CdiLAM presents an unusual substitution at position 4 of alpha-1-->6-mannan backbone by alpha-D-Araf. Unlike the non-fimbrial adhesin 62-72p, CdiLAM did not function as a hemagglutinin to human red blood cells. Experimental evidences pointed to CdiLAM as an adhesin of C. diphtheriae to human respiratory epithelial cells, thereby, contributing to the pathogenesis of diphtheria.