A DETAILED COMPARISON OF THE REFINED STRUCTURES OF CYTOCHROME-C(3) MOLECULES FROM 2 STRAINS IN DESULFOVIBRIO-VULGARIS - THE RELATIONSHIP BETWEEN THE HEME STRUCTURES AND THEIR REDOX PROPERTIES

The refined structures of the cytochrome c(3) molecules from Desulfovi brio vulgaris Miyazaki and Hildenborough have been compared in detail. Though there are no significant differences of the overall structure and spatial arrangement of four heme groups between two molecules, the re are some unique features with regard to the local structures near t he heme pockets. Two of the heme groups show significant differences i ncluding a hydrogen bonding scheme between the imidazole rings and wat er molecules in heme pocket. The water molecule near the heme 1 pocket in Miyazaki cytochrome c(3) is replaced by the C delta 1 atom of Leu9 in the Hildenborough structure. The rotation around the C alpha-C bet a bond of Leu9 results in the increase of the solvent accessibility of the portion of the heme 1 edge. On the other hand, in heme3 one water molecule is additionally included in the hydrogen bonding network wit h a N delta 1 atom of the imidazole ring and carbonyl oxygen atom of t he main chain in Hildenborough cytochrome c(3). This additional hydrog en bonding network will contribute to the possible passage between the imidazole ring and the molecular surface. These features have been re lated to the upheld shift of the C2 proton signals of NMR spectra and the low redox potentials of the cytochrome c(3) molecules of Desulfovi brio vulgaris Hildenborough in comparison with those from Miyazaki.