CRYSTAL-STRUCTURE OF ESCHERICHIA-COLI QOR QUINONE OXIDOREDUCTASE COMPLEXED WITH NADPH

The crystal structure of the homodimer of quinone oxidoreductase from Escherichia coli has been determined using the multiple isomorphous re placement method at 2.2 Angstrom resolution and refined to an R-factor of 14.1% The crystallographic asymmetric unit contains one functional dimer with the two subunits being related by a non-crystallographic 2 -fold symmetry axis. The model consists of two polypeptide chains (res idues 2 through 327), one NADPH molecule and one sulphate anion per su bunit, and 432 water molecules. Each subunit consists of two domains: a catalytic domain and a nucleotide-binding domain with the NADPH co-f actor bound in the cleft between domains. Quinone oxidoreductase has a n unusual nucleotide-binding fingerprint motif consisting of the seque nce AXXGXXG. The overall structure of quinone oxidoreductase shows str ong structural homology to that of horse liver alcohol dehydrogenase.