5vns
From Proteopedia
M.tb Antigen 85C Acyl-Enzyme Intermediate with Tetrahydrolipstatin
Structural highlights
Function[A85C_MYCTO] 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 (By similarity). Publication Abstract from PubMedMycobacterium tuberculosis antigen 85 (Ag85) enzymes catalyze the transfer of mycolic acid (MA) from trehalose monomycolate to produce the mycolyl arabinogalactan (mAG) or trehalose dimycolate (TDM). These lipids define the protective mycomembrane of mycobacteria. The current model of substrate binding within the active sites of Ag85s for the production of TDM is not sterically and geometrically feasible; additionally, this model does not account for the production of mAG. Furthermore, this model does not address how Ag85s limit the hydrolysis of the acyl-enzyme intermediate while catalyzing acyl transfer. To inform an updated model, we obtained an Ag85 acyl-enzyme intermediate structure that resembles the mycolated form. Here, we present a 1.45-A X-ray crystal structure of M. tuberculosis Ag85C covalently modified by tetrahydrolipstatin (THL), an esterase inhibitor that suppresses M. tuberculosis growth and mimics structural attributes of MAs. The mode of covalent inhibition differs from that observed in the reversible inhibition of the human fatty-acid synthase by THL. Similarities between the Ag85-THL structure and previously determined Ag85C structures suggest that the enzyme undergoes structural changes upon acylation, and positioning of the peptidyl arm of THL limits hydrolysis of the acyl-enzyme adduct. Molecular dynamics simulations of the modeled mycolated-enzyme form corroborate the structural analysis. From these findings, we propose an alternative arrangement of substrates that rectifies issues with the previous model and suggest a direct role for the beta-hydroxy of MA in the second half-reaction of Ag85 catalysis. This information affords the visualization of a complete mycolyltransferase catalytic cycle. Mycolyltransferase from Mycobacterium tuberculosis in covalent complex with tetrahydrolipstatin provides insights into antigen 85 catalysis.,Goins CM, Dajnowicz S, Smith MD, Parks JM, Ronning DR J Biol Chem. 2018 Mar 9;293(10):3651-3662. doi: 10.1074/jbc.RA117.001681. Epub, 2018 Jan 19. PMID:29352107[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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