Isolation and expression of a gene cluster responsible for biosynthesis of the glycopeptidolipid antigens of Mycobacterium avium.

Bacteria within the Mycobacterium avium complex are prominent in the environment and are a source of serious disseminated infections in patients with AIDS. Serovars of the M. avium complex are distinguished from all other mycobacteria and from one another by the presence of highly antigenic glycolipids, the glycopeptidolipids, on their surfaces. A genomic library of DNA from serovar 2 of the M. avium complex was constructed in the Escherichia coli-Mycobacterium shuttle cosmid, pYUB18, and used to clone and express in Mycobacterium smegmatis the genes responsible for the biosynthesis of the oligosaccharide segment of the M. avium serovar 2-specific glycopeptidolipid. The responsible gene cluster was mapped to a 22- to 27-kb functional region of the M. avium genome. The recombinant glycolipid was also isolated by high-pressure liquid chromatography and chemically characterized, by gas chromatography-mass spectrometry and fast atom bombardment-mass spectrometry, to demonstrate that the lipopeptide core originated in M. smegmatis, whereas the oligosaccharide segment arose from the cloned M. avium genes. This first-time demonstration of the cloning and expression, in a nonpathogenic mycobacterium, of the genes encoding complex cell wall glycoconjugates from a pathogenic mycobacterium presents a new approach for studying the role of such products in disease processes.