5ocj
Crystal structure of Ag85C bound to cyclophostin 8beta inhibitor
Structural highlights
FunctionA85C_MYCTU The antigen 85 proteins (FbpA, FbpB, FbpC) are responsible for the high affinity of mycobacteria to fibronectin, a large adhesive glycoprotein, which facilitates the attachment of M.tuberculosis to murine alveolar macrophages (AMs). They also help to maintain the integrity of the cell wall by catalyzing the transfer of mycolic acids to cell wall arabinogalactan and through the synthesis of alpha,alpha-trehalose dimycolate (TDM, cord factor). They catalyze the transfer of a mycoloyl residue from one molecule of alpha,alpha-trehalose monomycolate (TMM) to another TMM, leading to the formation of TDM.[1] [2] Publication Abstract from PubMedAn increasing prevalence of cases of drug-resistant tuberculosis requires the development of more efficacious chemotherapies. We previously reported the discovery of a new class of Cyclipostins and Cyclophostin (CyC) analogs exhibiting potent activity against Mycobacterium tuberculosis both in vitro and in infected macrophages. Competitive labeling/enrichment assays combined with MS have identified several serine or cysteine enzymes in lipid and cell wall metabolism as putative targets of these CyC compounds. These targets included members of the antigen 85 (Ag85) complex (i.e. Ag85A, Ag85B, and Ag85C), responsible for biosynthesis of trehalose dimycolate (TDM) and mycolylation of arabinogalactan. Herein, we used biochemical and structural approaches to validate the Ag85 complex as a pharmacological target of the CyC analogs. We found that CyC7beta, CyC8beta, and CyC17 bind covalently to the catalytic Ser124 residue in Ag85C, inhibit mycolyltransferase activity, i.e. the transfer of a fatty acid molecule onto trehalose, and reduce triacylglycerol synthase activity, a property previously attributed to Ag85A. Supporting these results, an X-ray structure of Ag85C in complex with CyC8beta disclosed that this inhibitor occupies Ag85C's substrate-binding pocket. Importantly, metabolic labeling of M. tuberculosis cultures revealed that the CyC compounds impair both TDM synthesis and mycolylation of arabinogalactan. Overall, our study provides compelling evidence that CyC analogs can inhibit the activity of the Ag85 complex in vitro and in mycobacteria, opening the door to a new strategy for inhibiting Ag85. The high-resolution crystal structure obtained will further guide the rational optimization of new CyC scaffolds with greater specificity and potency against M. tuberculosis. Cyclipostins and Cyclophostin analogs inhibit the antigen 85C from Mycobacterium tuberculosis both in vitro and in vivo.,Viljoen A, Richard M, Nguyen PC, Fourquet P, Camoin L, Paudal RR, Gnawali GR, Spilling CD, Cavalier JF, Canaan S, Blaise M, Kremer L J Biol Chem. 2018 Jan 4. pii: RA117.000760. doi: 10.1074/jbc.RA117.000760. PMID:29301937[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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