Mg2+ |
the addition of Mg2+ ions causes a conformational change in the enzyme's active site, breaking interactions known to keep farnesyl diphosphate in its inactive conformation. Wild-type protein shows relevant Mg2+ ion binding motifs. In the first binding motif, WT1, the Mg2+ ion is coordinated to D352 of beta-subunit, zinc-bound D297 of beta-subunit, two water molecules, and one oxygen atom from the alpha- and beta-phosphates of farnesyl diphosphate. The second binding motif, WT2, is identical with the exception of the zinc-bound D297 of beta-subunit being replaced by a water molecule in the Mg2+ coordination complex. In both motifs, a key hydrogen bond between a magnesium bound water and Cys1p bridges the two metallic binding sites, and thereby reduces the equilibrium distance between the reacting atoms of farnesyl diphosphate and protein-cysteine Cys1p. The free energy profiles calculated for these systems demonstrate that the two reactive atoms approach each other more readily in the presence of Mg2+. The flexible WT2 model has the lowest barrier towards the conformational change, suggesting it is the prefered Mg2+ binding motif |
Rattus norvegicus |
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