Mitochondrial cytochromes c: a comparative analysis.

The structures of 113 eukaryotic cytochrome c proteins of known sequence have been modeled in the oxidized state based on the existing crystallographic and NMR structures. The secondary structural elements and the overall three-dimensional structure were found to be maintained throughout the super-family, despite variability in the sequence of individual proteins. The iron axial ligands and their reciprocal orientation were found to be nearly universally conserved. Residues constituting the hydrophobic core of the protein are also very highly conserved or conservatively substituted. Certain surface-exposed charged as well as hydrophobic groups have also been found to be conserved to the same degree as core residues. Patterns of conservation of exposed residues identify regions of the protein that are likely to be critical for its function in electron transfer.