Ligand Binding and Conformational Change Coupling in the HAD Superfamily

Abstract

We aim to find for a representative member of the Haloalkanoate Dehalogenase Superfamily (HADSF) of phosphotransferases, β‐phosphoglucomutase (βPGM), how conformational changes are coupled to ligand binding. Most HADSF members, including βPGM, consist of a catalytic core Rossman fold and cap domain insert that folds over the substrate upon binding. The binding cavity between the two domains contains a site for two phosphoryl moieties, the “transferring” and “distal” sites. Solution X‐ray scattering studies, combined with molecular dynamics of βPGM in complex with ligands representing various substrate moieties show that occupation of the distal site is required for closure of the enzyme complex. Kclose values of these ligands were also determined via solution scattering data from ligand titrations and global fitting. These results show a large synergistic contribution (ΔG = 1.6 kcal/mol) to the conformational change between the two phosphate sites. However, covalent connection via the sugar ring has little energetic benefit indicating that this does not optimally align the ligand in the binding site (ground‐state destabilization), which contributes to the favorable energy of catalysis.