title: Nine-haem cytochrome c from Desulfovibrio desulfuricans ATCC 27774:primary sequence determination, crystallographic refinement at 1.8 and modelling studies of its interaction with the tetrahaem cytochrome c3.
abstract: A monomeric nine-haem cytochrome c (9Hcc) with 292 amino acid residues was isolated from cells of the sulfate- and nitrate-reducing bacterium Desulfovibrio desulfuricans ATCC 27774 grown under both nitrate- and sulfate-respiring conditions. The nucleotide sequence encoding the 292 residues was determined, allowing the correction of about 10% of the previous primary structure, determined from 1.8 A electron density maps. The refinement at 1.8 A resolution of the structural model was completed, giving an R-value of 16.5%. The nine haem groups are arranged into two tetrahaem clusters, located at both ends of the molecule, with Fe-Fe distances and local protein fold very similar to tetrahaem cytochromes c3, and the extra haem is located asymmetrically between the two regions. The new primary sequence determination confirmed the 39% sequence homology found between this cytochrome and the C-terminal region (residues 229-514) of the high-molecular-weight cytochrome c (Hmc) from D. vulgaris Hildenborough, providing strong evidence of structural similarity between 9Hcc and the C-terminal region of Hmc. The interaction between 9Hcc and the tetrahaem cytochrome c3 from the same organism was studied by modelling methods, and the results suggest that a specific interaction is possible between haem 4 of tetrahaem cytochrome c3 and haem 1 or haem 2 of 9Hcc, in agreement with previous kinetic experiments which showed the catalytic effect of the tetrahaem cytochrome c3 upon the reduction of 9Hcc by the [NiFe] hydrogenase from D. desulfuricans ATCC 27774. These studies suggest a role for 9Hcc as part of the assembly of redox proteins involved in recycling the molecular hydrogen released by the cell as a result of substrate oxidation.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal.
authors.forename: P M
authors.initials: PM
authors.lastname: Matias
authors.forename: L M
authors.initials: LM
authors.lastname: Saraiva
authors.forename: C M
authors.initials: CM
authors.lastname: Soares
authors.forename: A V
authors.initials: AV
authors.lastname: Coelho
authors.forename: J
authors.initials: J
authors.lastname: LeGall
authors.forename: M A
authors.initials: MA
authors.lastname: Carrondo
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism; D003901:Desulfovibrio / Q000201:enzymology*; D006418:Heme; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017421:Sequence Analysis
chemical_list: D003574:Cytochrome c Group; D006418:Heme; C017165:cytochrome c(3)