Structural and functional insights into the flexible beta-hairpin of glycerol dehydrogenase

Abstract

During glycerol metabolism, the initial step of glycerol oxidation is catalysed by glycerol dehydrogenase (GDH), which converts glycerol to dihydroxyacetone in a NAD(+)-dependent manner via an ordered Bi-Bi kinetic mechanism. Structural studies conducted with GDH from various species have mainly elucidated structural details of the active site and ligand binding. However, the structure of the full GDH complex with both cofactor and substrate bound is not determined, and thus, the structural basis of the kinetic mechanism of GDH remains unclear. Here, we report the crystal structures of Escherichia coli GDH with a substrate analogue bound in the absence or presence of NAD(+). Structural analyses including molecular dynamics simulations revealed that GDH possesses a flexible beta-hairpin, and that during the ordered progression of the kinetic mechanism, the flexibility of the beta-hairpin is reduced after NAD(+) binding. It was also observed that this alterable flexibility of the beta-hairpin contributes to the cofactor binding and possibly to the catalytic efficiency of GDH. These findings suggest the importance of the flexible beta-hairpin to GDH enzymatic activity and shed new light on the kinetic mechanism of GDH.