title: Heme packing motifs revealed by the crystal structure of the tetra-heme cytochrome c554 from Nitrosomonas europaea.
abstract: Cytochrome c554 (cyt c554), a tetra-heme cytochrome from Nitrosomonas europaea, is an essential component in the biological nitrification pathway. In N. europaea, ammonia is converted to hydroxylamine, which is then oxidized to nitrite by hydroxylamine oxidoreductase (HAO). Cyt c554 functions in the latter process by accepting pairs of electrons from HAO and transferring them to a cytochrome acceptor. The crystal structure of cyt c554 at 2.6 A resolution shows a predominantly alpha-helical protein with four covalently attached hemes. The four hemes are arranged in two pairs such that the planes of the porphyrin rings are almost parallel and overlapping at the edge; corresponding heme arrangements are observed in other multi-heme proteins. Striking structural similarities are evident between the tetra-heme core of cyt c554 and hemes 3-6 of HAO, which suggests an evolutionary relationship between these redox partners.
authors.affiliation: Graduate Option in Biochemistry, California Institute of Technology, Pasadena 91125, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Iverson
authors.forename: D M
authors.initials: DM
authors.lastname: Arciero
authors.forename: B T
authors.initials: BT
authors.lastname: Hsu
authors.forename: M S
authors.initials: MS
authors.lastname: Logan
authors.forename: A B
authors.initials: AB
authors.lastname: Hooper
authors.forename: D C
authors.initials: DC
authors.lastname: Rees
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009606:Nitrosomonas / Q000737:chemistry*; D010088:Oxidoreductases / Q000737:chemistry; D017433:Protein Structure, Secondary
chemical_list: D003574:Cytochrome c Group; C083951:cytochrome c553; D006418:Heme; C022302:cytochrome C-552; D010088:Oxidoreductases; C021401:hydroxylamine dehydrogenase