Retrobiosynthetic Approach Delineates the Biosynthetic Pathway and the Structure of the Acyl Chain of Mycobacterial Glycopeptidolipids

• Published in: The Journal of biological chemistry 2012-08, Vol.287 (36), p.30677-30687
• Main Authors: Vats, Archana, Singh, Anil Kumar, Mukherjee, Raju, Chopra, Tarun, Ravindran, Madhu Sudhan, Mohanty, Debasisa, Chatterji, Dipankar, Reyrat, Jean-Marc, Gokhale, Rajesh S.
• Format: Article
• Language: English
• Subjects: Acyl Carrier Protein; Enzymology; Fatty Acid; Fatty Acids - metabolism; Fatty Acyl AMP Ligase; Glycolipids - biosynthesis; Glycosylation; Hydroxylation; Lipids; Mycobacteria; Mycobacterium smegmatis - metabolism; Oligopeptides - biosynthesis; Polyketide Synthase; Polyketides
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.384966

Glycopeptidolipids (GPLs) are dominant cell surface molecules present in several non-tuberculous and opportunistic mycobacterial species. GPLs from Mycobacterium smegmatis are composed of a lipopeptide core unit consisting of a modified C26-C34 fatty acyl chain that is linked to a tetrapeptide (Phe-Thr-Ala-alaninol). The hydroxyl groups of threonine and terminal alaninol are further modified by glycosylations. Although chemical structures have been reported for 16 GPLs from diverse mycobacteria, there is still ambiguity in identifying the exact position of the hydroxyl group on the fatty acyl chain. Moreover, the enzymes involved in the biosynthesis of the fatty acyl component are unknown. In this study we show that a bimodular polyketide synthase in conjunction with a fatty acyl-AMP ligase dictates the synthesis of fatty acyl chain of GPL. Based on genetic, biochemical, and structural investigations, we determine that the hydroxyl group is present at the C-5 position of the fatty acyl component. Our retrobiosynthetic approach has provided a means to understand the biosynthesis of GPLs and also resolve the long-standing debate on the accurate structure of mycobacterial GPLs. Background: Precise chemical structure and biosynthetic pathway of the acyl chain of mycobacterial glycopeptidolipids (GPLs) is unknown. Results: Polyketide synthases dictate biosynthesis and determine hydroxylation at C-5 position of the GPL acyl chain. Conclusions: Retrobiosynthetic studies establish the role of bimodular polyketide synthase and fatty acyl-AMP-ligase in GPL biosynthesis. Significance: The long-standing ambiguity on the accurate structure and the biosynthetic mechanism of GPLs was resolved.