title: High-resolution structures of the oxidized and reduced states of cytochrome c554 from Nitrosomonas europaea.
abstract: Cytochrome c554 (cyt c554) is a tetra-heme cytochrome involved in the oxidation of NH3 by Nitrosomonas europaea. The X-ray crystal structures of both the oxidized and dithionite-reduced states of cyt c554 in a new, rhombohedral crystal form have been solved by molecular replacement, at 1.6 A and 1.8 A resolution, respectively. Upon reduction, the conformation of the polypeptide chain changes between residues 175 and 179, which are adjacent to hemes III and IV. Cyt c554 displays conserved heme-packing motifs that are present in other heme-containing proteins. Comparisons to hydroxylamine oxidoreductase, the electron donor to cyt c554, and cytochrome c nitrite reductase, an enzyme involved in nitrite ammonification, reveal substantial structural similarity in the polypeptide chain surrounding the heme core environment. The structural determinants of these heme-packing motifs extend to the buried water molecules that hydrogen bond to the histidine ligands to the heme iron. In the original structure determination of a tetragonal crystal form, a cis peptide bond between His129 and Phe130 was identified that appeared to be stabilized by crystal contacts. In the rhombohedral crystal form used in the present high-resolution structure determination, this peptide bond adopts the trans conformation, but with disallowed angles of phi and psi.
authors.affiliation: Division of Chemistry and Chemical Engineering and Howard Hughes Medical Institute, MC 147-75 CH, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Iverson
authors.forename: D M
authors.initials: DM
authors.lastname: Arciero
authors.forename: A B
authors.initials: AB
authors.lastname: Hooper
authors.forename: D C
authors.initials: DC
authors.lastname: Rees
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006639:Histidine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009606:Nitrosomonas / Q000201:enzymology*; D010084:Oxidation-Reduction; D010649:Phenylalanine / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding
chemical_list: D003574:Cytochrome c Group; C083951:cytochrome c553; D006418:Heme; D010649:Phenylalanine; D006639:Histidine; C022302:cytochrome C-552