title: TPR domain of NrfG mediates complex formation between heme lyase and formate-dependent nitrite reductase in Escherichia coli O157:H7.
abstract: Escherichia coli synthesize C-type cytochromes only during anaerobic growth in media supplemented with nitrate and nitrite. The reduction of nitrate to ammonium in the periplasm of Escherichia coli involves two separate periplasmic enzymes, nitrate reductase and nitrite reductase. The nitrite reductase involved, NrfA, contains cytochrome C and is synthesized coordinately with a membrane-associated cytochrome C, NrfB, during growth in the presence of nitrite or in limiting nitrate concentrations. The genes NrfE, NrfF, and NrfG are required for the formate-dependent nitrite reduction pathway, which involves at least two C-type cytochrome proteins, NrfA and NrfB. The NrfE, NrfF, and NrfG genes (heme lyase complex) are involved in the maturation of a special C-type cytochrome, apocytochrome C (apoNrfA), to cytochrome C (NrfA) by transferring a heme to the unusual heme binding motif of the Cys-Trp-Ser-Cys-Lys sequence in apoNrfA protein. Thus, in order to further investigate the roles of NrfG in the formation of heme lyase complex (NrfEFG) and in the interaction between heme lyase complex and formate-dependent nitrite reductase (NrfA), we determined the crystal structure of NrfG at 2.05 A. The structure of NrfG showed that the contact between heme lyase complex (NrfEFG) and NrfA is accomplished via a TPR domain in NrfG which serves as a binding site for the C-terminal motif of NrfA. The portion of NrfA that binds to TPR domain of NrfG has a unique secondary motif, a helix followed by about a six-residue C-terminal loop (the so called "hook conformation"). This study allows us to better understand the mechanism of special C-type cytochrome assembly during the maturation of formate-dependent nitrite reductase, and also adds a new TPR binding conformation to the list of TPR-mediated protein-protein interactions.
authors.affiliation: College of Medicine, Seoul National University, Yongon-Dong, Seoul 110-799, Korea.
authors.forename: Dohyun
authors.initials: D
authors.lastname: Han
authors.forename: Kyunggon
authors.initials: K
authors.lastname: Kim
authors.forename: Jongkil
authors.initials: J
authors.lastname: Oh
authors.forename: Jungeun
authors.initials: J
authors.lastname: Park
authors.forename: Youngsoo
authors.initials: Y
authors.lastname: Kim
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019453:Escherichia coli O157 / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005798:Genes, Bacterial; D008190:Lyases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009572:Nitrite Reductases / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment