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Dissecting the Structural and Chemical Determinants of the “Open-to-Closed” Motion in the Mannosyltransferase PimA from Mycobacteria

Abstract : The phosphatidyl-myo-inositol mannosyltransferase A (PimA) is an essential peripheral membrane glycosyltransferase that initiates the biosynthetic pathway of phosphatidyl-myo-inositol mannosides (PIMs), key structural elements and virulence factors of Mycobacterium tuberculosis. PimA undergoes functionally important conformational changes, including (i) α-helix-to-β-strand and β-strand-to-α-helix transitions and (ii) an "open-to-closed" motion between the two Rossmann-fold domains, a conformational change that is necessary to generate a catalytically competent active site. In previous work, we established that GDP-Man and GDP stabilize the enzyme and facilitate the switch to a more compact active state. To determine the structural contribution of the mannose ring in such an activation mechanism, we analyzed a series of chemical derivatives, including mannose phosphate (Man-P) and mannose pyrophosphate-ribose (Man-PP-RIB), and additional GDP derivatives, such as pyrophosphate ribose (PP-RIB) and GMP, by the combined use of X-ray crystallography, limited proteolysis, circular dichroism, isothermal titration calorimetry, and small angle X-ray scattering methods. Although the β-phosphate is present, we found that the mannose ring, covalently attached to neither phosphate (Man-P) nor PP-RIB (Man-PP-RIB), does promote the switch to the active compact form of the enzyme. Therefore, the nucleotide moiety of GDP-Man, and not the sugar ring, facilitates the "open-to-closed" motion, with the β-phosphate group providing the high-affinity binding to PimA. Altogether, the experimental data contribute to a better understanding of the structural determinants involved in the "open-to-closed" motion not only observed in PimA but also visualized and/or predicted in other glycosyltransfeases. In addition, the experimental data might prove to be useful for the discovery and/or development of PimA and/or glycosyltransferase inhibitors.
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Submitted on : Tuesday, April 27, 2021 - 5:05:18 PM
Last modification on : Thursday, April 7, 2022 - 10:10:44 AM

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Ane Rodrigo-Unzueta, Mattia Ghirardello, Saioa Urresti, Ignacio Delso, David Giganti, et al.. Dissecting the Structural and Chemical Determinants of the “Open-to-Closed” Motion in the Mannosyltransferase PimA from Mycobacteria. Biochemistry, 2020, 59 (32), pp.2934-2945. ⟨10.1021/acs.biochem.0c00376⟩. ⟨pasteur-03210105⟩



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