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>Crystal structure of Mycobacterium tuberculosis O6-methylguanine-DNA methyltransferase protein clusters assembled on to damaged DNA
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Crystal structure of Mycobacterium tuberculosis O6-methylguanine-DNA methyltransferase protein clusters assembled on to damaged DNA
piMycobacterium tuberculosis O/isup6/sup-methylguanine-DNA methyltransferase (iMt/iOGT) contributes to protect the bacterial GC-rich genome against the pro-mutagenic potential of Osup6/sup-methylated guanine in DNA. Several strains of iM. tuberculosis/i found worldwide encode a point-mutated iO/isup6/sup-methylguanine-DNA methyltransferase (OGT) variant (iMt/iOGT-R37L), which displays an arginine-to-leucine substitution at position 37 of the poorly functionally characterized N-terminal domain of the protein. Although the impact of this mutation on the iMt/iOGT activity has not yet been proved iin vivo/i, we previously demonstrated that a recombinant iMt/iOGT-R37L variant performs a suboptimal alkylated-DNA repair iin vitro/i, suggesting a direct role for the Argsup37/sup-bearing region in catalysis. The crystal structure of iMt/iOGT complexed with modified DNA solved in the present study reveals details of the protein–protein and protein–DNA interactions occurring during alkylated-DNA binding, and the protein capability also to host unmodified bases inside the active site, in a fully extrahelical conformation. Our data provide the first experimental picture at the atomic level of a possible mode of assembling three adjacent iMt/iOGT monomers on the same monoalkylated dsDNA molecule, and disclose the conformational flexibility of discrete regions of iMt/iOGT, including the Argsup37/sup-bearing random coil. This peculiar structural plasticity of iMt/iOGT could be instrumental to proper protein clustering at damaged DNA sites, as well as to protein–DNA complexes disassembling on repair./p
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