Structure of cytochrome c(2) from Rhodospirillum centenum

Cytochrome c(2) from the purple photosynthetic bacterium Rhodospirillum cen tenum has been crystallized by the sitting-drop vapour-diffusion method. Th e crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit- cell parameters a = 29.7, b = 59.9, c = 65.4 Angstrom, and diffract to a re solution limit of 1.7 Angstrom. The Fe-atom position was determined from it s anomalous scattering contribution and a molecular-replacement solution wa s calculated. The correctness of the solution was confirmed by parallel iso morphous replacement studies. The resulting model has a type I cytochrome f old with two features, an extended alpha -helix and a surface-charge distri bution, that are distinctive to this protein. The implications of these str uctural features for the ability of the cytochrome to serve as an electron carrier are discussed.