Coordination of the heme iron in the low-potential cytochromes c-553 from Desulfovibrio vulgaris and Desulfovibrio desulfuricans. Different chirality of the axially bound methionine in the oxidized and reduced states.
The coordination geometry at the heme iron of the cytochromes c-553 from Desulfovibrio vulgaris and Desulfovibrio desulfuricans was investigated by 1H-nuclear magnetic resonance and circular dichroism spectroscopy. Individual assignments were obtained for heme c and the axial ligands. From studies of nuclear Overhauser enhancements the axial histidine imidazole ring orientation relative to the heme group was found to coincide with other c-type cytochromes. In contrast, a new structure was observed for the axial methionine in the reduced cytochromes c-553. This includes S chirality at the iron-bound sulfur atom, but compared to cytochromes c-551 from Pseudomonads and Rhodopseudomonas gelatinosa and cytochrome c5 from Pseudomonas mendocina, which also contain S-chiral methionine, a different spatial arrangement of the gamma- and beta-methylene groups and the alpha carbon of methionine prevails. For the ferricytochromes c-553 R chirality was found for the iron-bound sulfur. This is the first observation of different methionine chirality in different oxidation states of the same c-type cytochrome.
D001665:Binding Sites; D003574:Cytochrome c Group / Q000378:metabolism*; D003901:Desulfovibrio / Q000378:metabolism*; D006418:Heme / Q000032:analysis*; D007501:Iron / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D008715:Methionine; D010084:Oxidation-Reduction; D011485:Protein Binding; D011487:Protein Conformation; D013045:Species Specificity
D003574:Cytochrome c Group; C083951:cytochrome c553; D006418:Heme; C022302:cytochrome C-552; D008715:Methionine; D007501:Iron