Crystal structure of substrate free form of glycerol dehydratase

Glycerol dehydratase (GDH) and diol dehydratase (DDH) are highly homologous isofunctional enzymes that catalyze the elimination of water from glycerol and 1,2-propanediol (1,2-PD) to the corresponding aldehyde via a coenzyme B(12)-dependent radical mechanism. The crystal structure of substrate free form of GDH in complex with cobalamin and K(+) has been determined at 2.5 A resolution. Its overall fold and the subunit assembly closely resemble those of DDH. Comparison of this structure and the DDH structure, available only in substrate bound form, shows the expected change of the coordination of the essential K(+) from hexacoordinate to heptacoordinate with the displacement of a single coordinated water by the substrate diol. In addition, there appears to be an increase in the rigidity of the K(+) coordination (as measured by lower B values) upon the binding of the substrate. Structural analysis of the locations of conserved residues among various GDH and DDH sequences has aided in identification of residues potentially important for substrate preference or specificity of protein-protein interactions.