Phenolic glycolipids (PGLs) are polyketide-derived virulence factors produced by Mycobacterium tuberculosis, M. leprae, and other mycobacterial pathogens. We have combined bioinformatic, genetic, biochemical, and chemical biology approaches to illuminate the mechanism of chain initiation required for assembly of the p-hydroxyphenyl-polyketide moiety of PGLs. Our studies have led to the identification of a stand-alone, didomain initiation module, FadD22, comprised of a p-hydroxybenzoic acid adenylation domain and an aroyl carrier protein domain. FadD22 forms an acyl-S-enzyme covalent intermediate in the p-hydroxyphenyl-polyketide chain assembly line. We also used this information to develop a small-molecule inhibitor of PGL biosynthesis. Overall, these studies provide insights into the biosynthesis of an important group of small-molecule mycobacterial virulence factors and support the feasibility of targeting PGL biosynthesis to develop new drugs to treat mycobacterial infections.
Bibliographical noteFunding Information:
We thank Albert Morrishow (Weill Medical College) and Dr. George Sukenick, Hui Fang, Hui Liu, and Sylvi Rusli (Memorial Sloan-Kettering Cancer Center [MSKCC]) for mass spectral analyses. Generous financial support has been provided by the National Institutes of Health (grant AI069209 to L.E.N.Q.), Stavros S. Niarchos Foundation (L.E.N.Q.), NYSTAR Watson Investigator Program (D.S.T.), William Randolph Hearst Foundation (L.E.N.Q. and D.S.T.), William H. Goodwin and Alice Goodwin and the Commonwealth Foundation for Cancer Research (D.S.T.), and MSKCC Experimental Therapeutics Center (D.S.T.). L.E.N.Q. was responsible for designing the study, directing the project, and writing the manuscript. D.S.T. oversaw the synthetic aspects of the project. D.S.T., X.L., J.-S.R., J.A.F., K.L.S., and C.E.S. edited the manuscript. J.A.F. contributed to the experimental design and conducted the enzyme characterization and inhibition experiments. K.L.S. contributed to the experimental design and conducted the genetic analysis and PGL inhibition experiments. C.E.S. performed the MS analysis. X.L. and J.-S.R. developed and executed the synthesis of pHB-AMS.