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The complex cellular envelope is one of the major reasons behind the survival in hostile conditions and the emergence of the drug-resisting properties of mycobacteria. Phosphatidyl-myo-inositol hexamannoside (PIM6), Lipomannan (LM), and Lipoarabinomannan (LAM) are important structural constituents of the cell envelope and have roles in modulating host immune functions. Phosphatidyl-myo-inositol (PI) is first mannosylated at the 2-position of the inositol group by phosphatidyl-myo-inositol mannosyltransferase A (PimA) to produce phosphatidyl-myo-inositol monomannoside (PIM1). This PIM1 is then further mannosylated at the 6-position of the inositol group by phosphatidyl-myo-inositol mannosyltransferase B' (PimB') utilizing GDP-mannose as the mannose-donor to synthesize phosphatidyl-myo-inositol dimannoside (PIM2) and GDP. Further mannosylation and acylation on PIM2 produce Ac1/2PIM4, which can then be converted to either Ac1/2PIM6 or LM/LAM. Detailed functional mechanism of how PimB' transfers the mannose sugar to PIM1 is not understood. Using molecular docking, the interactions of PimB' with the substrate PIM1 and the product PIM2 are analyzed here. Molecular dynamics (MD) simulations of PimB' with the substrates and the products were performed for 300ns to find out critical residues involved in the mannose-transfer reaction. Docking and MD analyses indicated the residues R206 and R210 bind both PIM1 and PIM2 and are critical in the mannose-transfer reaction. The residues 120HEVGWSMLPGS130 and 281RTRGGGL288 were involved in the transfer of PIM1 from the active site. The residues 18IGG20, K211, E290, G291, 294IV295, and E298 were also important in the mannosylation reaction. The crucial residues obtained from this study may help design novel drugs against mycobacterial PimB'. Copyright © 2022 Elsevier Inc. All rights reserved.


Gourab Bhattacharje, Amit Ghosh, Amit Kumar Das. In-silico identification of critical residues in the mannose-transfer mechanism of phosphatidyl-myo-inositol mannosyltransferase B'. Biochemical and biophysical research communications. 2022 Sep 17;621:14-19

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PMID: 35809342

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