Analysis of the genes encoding the antigen 85 complex and MPT51 from Mycobacterium avium

The components of the fibronectin-binding antigen 85 complex (85A, 85B, and 85C) and the related protein MPB/MPT51 are major secreted proteins in Mycobacterium tuberculosis and Mycobacterium bovis BCG. The fbpA, fbpC, and mpt51 genes encoding 85A, 85C, and MPT51, respectively, were isolated from Mycobacterium avium and sequenced in this study. The structures of these genes, and that of the fbpB gene encoding the 85B protein, were conserved in these three species. The secreted amounts of 85A, 85B, 85C, and MPB/MPT51 were compared for M. tuberculosis, BCG, and M. avium. These four proteins were found in large amounts in the culture filtrates from M. tuberculosis and BCG. In contrast, in the culture filtrate from M. avium, 85B and MPT51 were abundant whereas 85A and 85C were hardly found, in spite of the presence of the encoding genes. The difference in the secretion amounts might be regulated at the transcription level. These facts might reflect host immunopathogenesis, the protective immunities against infections, and the drug susceptibilities of these organisms.