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  • Title: Structure and function of a hexameric copper-containing nitrite reductase.
    Author: Nojiri M, Xie Y, Inoue T, Yamamoto T, Matsumura H, Kataoka K, Deligeer, Yamaguchi K, Kai Y, Suzuki S.
    Journal: Proc Natl Acad Sci U S A; 2007 Mar 13; 104(11):4315-20. PubMed ID: 17360521.
    Abstract:
    Dissimilatory nitrite reductase (NIR) is a key enzyme in denitrification, catalyzing the first step that leads to gaseous products (NO, N(2)O, and N(2)). We have determined the crystal structure of a Cu-containing NIR from a methylotrophic denitrifying bacterium, Hyphomicrobium denitrificans, at 2.2-A resolution. The overall structure of this H. denitrificans NIR reveals a trigonal prism-shaped molecule in which a monomer consisting of 447 residues and three Cu atoms is organized into a unique hexamer (i.e., a tightly associated dimer of trimers). Each monomer is composed of an N-terminal region containing a Greek key beta-barrel folding domain, cupredoxin domain I, and a C-terminal region containing cupredoxin domains II and III. Both cupredoxin domains I and II bind one type 1 Cu and are combined with a long loop comprising 31 amino acid residues. The type 2 Cu is ligated at the interface between domain II of one monomer and domain III of an adjacent monomer. Between the two trimeric C-terminal regions are three interfaces formed by an interaction between the domains I, and the type 1 Cu in the domain is required for dimerization of the trimer. The type 1 Cu in domain II functions as an electron acceptor from an electron donor protein and then transfers an electron to the type 2 Cu, binding the substrate to reduce nitrite to NO. The discussion of the intermolecular electron transfer process from cytochrome c(550) to the H. denitrificans NIR is based on x-ray crystallographic and kinetic results.
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