GLYCOPEPTIDOLIPID BIOSYNTHESIS IN AVIUM COMPLEX

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The clinical management of acquired immune deficiency syndrome (AIDS) is more difficult because of opportunistic infections, the more serious of which are those involving members of the Mycobacterium avium complex. Because members of the M. avium complex are resistant to most antimycobacterial drugs, therapy usually involves 4-6 drugs and prognosis is poor. Because of the strategic location of the glycopeptidolipid antigens (GPL) in the cell wall and the fact that they are unique to members of the M. avium complex, inhibition of GPL biosynthesis should lead to a selective means of treating infections caused by these organisms. Previous studies in this laboratory have lead to the isolation of rough-colony M. avium complex variants and the development of radiolabeling techniques which can be used to study the biosynthesis of the GPL components and related precursors. The long term objective of this research proposal is to investigate the biosynthetic pathway of the GPL in an effort to identify metabolic targets for selective antimicrobial activity. The immediate objective will be to identify potential precursors in GPL biosynthesis and utilize those precursors in a cell-free system to further delineate the biosynthetic pathway of the GPL components. Two approaches will be taken to identify the potential precursors. In the first approach mycobacteria will be treated with drugs which have the potential to inhibit GPL biosynthesis and radiolabeling techniques will be used to identify concomitant accumulation of radiolabeled precursors. In the second approach, rough-colony variants, which lack the ability to complete the synthesis of GPL components but contain initial products of GPL synthesis, will also be used to identify potential precursors. Ability of the potential precursors to participate in GPL biosynthesis will be confirmed by using a cell-free system which has been developed to study in vitro biosynthesis of GPL components. Once the precursors have been confirmed, then the cell-free system will be utilized to examine the effect of specific inhibitors on GPL biosynthesis. These studies should eventually lead to the identification of key enzymes in the GPL biosynthetic pathway, thus making it possible to develop selective antimicrobial therapy for treating M. avium complex infections.