CRYSTAL-STRUCTURE OF NADH-CYTOCHROME-B5 REDUCTASE FROM PIG-LIVER AT 2.4-ANGSTROM RESOLUTION

The three-dimensional structure of NADH-cytochrome bs reductase from pig liver microsomes has been determined at 2.4 Angstrom resolution by X-ray crystallography. The molecular structure reveals two domains, the FAD binding domain and the NADH domain. A large cleft Lies between these two domains and contains the binding site for the FAD prosthetic group. The backbone structure of the FAD binding domain has a great similarity to that of ferredoxin-NADP(+) reductase [Karplus, P. A., Daniels, M. J., & Herriott, J. R. (1991) Science 251, 60-65], in spite of the relatively low sequence homology (about 15%) between the two enzymes. On the other hand, the structure of the NADH domain has several structural differences from that of the NADP(+) domain of ferredoxin-NADP(+) reductase. The size of the cleft between the two domains is larger in NADH-cytochrome b(5) reductase than in ferredoxin-NADP(+) reductase, which may be responsible for the observed difference in the nucleotide accessibility in the two enzymes.