CRYSTAL-STRUCTURE OF HUMAN GLYOXALASE .1. EVIDENCE FOR GENE DUPLICATION AND 3D DOMAIN SWAPPING

The zinc metalloenzyme glyoxalase I catalyses the glutathione-dependen t inactivation of toxic methylglyoxal. The structure of the dimeric hu man enzyme in complex with S-benzyl-glutathione has been determined by multiple isomorphous replacement (MIR) and refined at 2.2 Angstrom re solution, Each monomer consists of two domains. Despite only law seque nce homology between them, these domains are structurally equivalent a nd appear to have arisen by a gene duplication. On the other hand, the re Is no structural homology to the (glutathione binding domain' found in other glutathione-linked proteins. 3D domain swapping of the N- an d C-terminal domains has resulted in the active site. being situated i n the dimer interface, with the inhibitor and essential zinc ion inter acting with side chains from both subunits. Two structurally equivalen t residues from each domain contribute to a square pyramidal coordinat ion of the zinc ion, rarely seen in zinc enzymes. Comparison of glyoxa lase I with other known structures shows the enzyme to belong to a nem structural family which includes the Fe2+-dependent dihydroxybiphenyl dioxygenase and the bleomycin resistance protein. This structural fam ily appears to allow members to form with or without domain swapping.