title: Structural and mechanistic insights into the electron flow through protein for cytochrome c-tethering copper nitrite reductase.
abstract: Copper-containing nitrite reductases (CuNiRs), which catalyse the reversible one-electron reduction of nitrite to nitric oxide, are members of a large family of multi-copper enzymes that require an interprotein electron transfer (ET) reaction with redox partner proteins. Here, we show that the naturally fused type of CuNiR tethering a cytochrome c (Cyt c) at the C-terminus folds as a unique trimeric domain-swapped structure and has a self-sufficient electron flow system. The C-terminal Cyt c domain is located at the surface of the type 1 copper (T1Cu) site in the N-terminal CuNiR domain from the adjacent subunit, the heme-to-Cu distance (10.6 Å) of which is comparable to the transient ET complex of normal CuNiR with Cyt c. The structural aspects for the domain-domain interface and the ET kinetics indicate that the Cyt c-CuNiR domain interaction should be highly transient. The further electrochemical analysis of the interprotein ET reaction with a cognate redox partner protein suggested that an electron is directly transferred from the partner to the T1Cu. Structural and mechanistic comparisons of Cyt c-CuNiR with another cupredoxin-tethering CuNiR highlight the behaviours of extra domains on the fusion types of CuNiRs required for ET through proteins.
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Aiko
authors.initials: A
authors.lastname: Tsuda
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Ishikawa
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Koteishi
authors.forename: Kosuke
authors.initials: K
authors.lastname: Tange
authors.forename: Yohta
authors.initials: Y
authors.lastname: Fukuda
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Inoue
authors.forename: Masaki
authors.initials: M
authors.lastname: Nojiri
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism*; D004579:Electron Transport; D008958:Models, Molecular; D009572:Nitrite Reductases / Q000737:chemistry* / Q000378:metabolism*; D010084:Oxidation-Reduction; D054730:Protein Interaction Domains and Motifs; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D031161:Pseudoalteromonas / Q000201:enzymology; D011675:Pulse Radiolysis; D055672:Static Electricity
chemical_list: D001426:Bacterial Proteins; D021122:Protein Subunits; D045304:Cytochromes c; D009572:Nitrite Reductases; C052695:nitrite reductase, copper-containing
keywords: X-ray crystal structure; copper nitrite reductase; multi-domain protein; protein electron transfer