title: Further characterization of the two tetraheme cytochromes c3 from Desulfovibiro africanus: nucleotide sequences, EPR spectroscopy and biological activity.
abstract: The genes encoding the basic and acidic tetraheme cytochromes c3 from Desulfovibrio africanus have been sequenced. The corresponding amino acid sequences of the basic and acidic cytochromes c3 indicate that the mature proteins consist of a single polypeptide chain of 117 and 103 residues, respectively. Their molecular masses, 15102 and 13742 Da, respectively, determined by mass spectrometry, are in perfect agreement with those calculated from their amino acid sequences. Both D. africanus cytochromes c3 are synthesized as precursor proteins with signal peptides of 23 and 24 residues for the basic and acidic cytochromes, respectively. These cytochromes c3 exhibit the main structural features of the cytochrome c3 family and contain the 16 strictly conserved cysteine + histidine residues directly involved in the heme binding sites. The D. africanus acidic cytochrome c3 differs from all the other homologous cytochromes by its low content of basic residues and its distribution of charged residues in the amino acid sequence. The presence of four hemes per molecule was confirmed by EPR spectroscopy in both cytochromes c3. The g-value analysis suggests that in both cytochromes, the angle between imidazole planes of the axial histidine ligands is close to 90 degrees for one heme and much lower for the three others. Moreover, an unusually high exchange interaction (approximately 10[-2] cm[-1]) was evidenced between the highest potential heme (-90 mV) and one of the low potential hemes in the basic cytochrome c3. The reactivity of D. africanus cytochromes c3 with heterologous [NiFe] and [Fe] hydrogenases was investigated. Only the basic one interacts with the two types of hydrogenase to achieve efficient electron transfer, whereas the acidic cytochrome c3 exchanges electrons specifically with the basic cytochrome c3. The difference in the specificity of the two D. africanus cytochromes c3 has been correlated with their highly different content of basic and acidic residues.
authors.affiliation: Unité de Bioénergétique et Ingénierie des protéines, Institut de Biologie Structurale et Microbiologie, CNRS, Marseille, France.
authors.forename: V
authors.initials: V
authors.lastname: Magro
authors.forename: L
authors.initials: L
authors.lastname: Pieulle
authors.forename: N
authors.initials: N
authors.lastname: Forget
authors.forename: B
authors.initials: B
authors.lastname: Guigliarelli
authors.forename: Y
authors.initials: Y
authors.lastname: Petillot
authors.forename: E C
authors.initials: EC
authors.lastname: Hatchikian
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D003574:Cytochrome c Group / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D003901:Desulfovibrio / Q000201:enzymology* / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D005798:Genes, Bacterial; D006418:Heme / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006864:Hydrogenase / Q000378:metabolism; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D013057:Spectrum Analysis
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D006418:Heme; C017165:cytochrome c(3); C043296:nickel-iron hydrogenase; D006864:Hydrogenase