| Primary Identifier | IPR002327 | Type | Family |
| Short Name | Cyt_c_1A/1B |
| description | Cytochromes c (cytC) can be defined as electron-transfer proteins having one or several haem c groups, bound to the protein by one or, more generally, two thioether bonds involving sulfhydryl groups of cysteine residues. The fifth haem iron ligand is always provided by a histidine residue. CytC possess a wide range of properties and function in a large number of different redox processes.Ambler []recognised four classes of cytC. Class I includes the low-spin soluble cytC of mitochondria and bacteria, with the haem-attachment site towards the N terminus, and the sixth ligand provided by a methionine residue about 40 residues further on towards the C terminus []. On the basis of sequence similarity, class I cytC were further subdivided into five classes, IA to IE. Class IB includes the eukaryotic mitochondrial cyt C and prokaryotic 'short' cyt C2 exemplified by Rhodopila globiformis cyt C2; Class IA includes 'long' cyt C2, such as Rhodospirillum rubrum cyt C2 and Aquaspirillum itersonii cyt C-550, which have several extra loops by comparison with Class IB cyt C.Class I cytC has a characterised fold which comprises 5 α-helices arranged in a unique tertiary structure and a conserved N-terminal sequence -Cys-Xxx-Xxx-Cys-His- where the cysteines mediate the covalent cross-linking of the heme to the protein and the His [].The 3D structures of a considerable number of class IA and IB cytC have been determined. The proteins consist of 3-6 α-helices; the three most conserved 'core' helices form a 'basket' around the haem group, with one haem edge exposed to the solvent. Most class I cytC have conserved aromatic residues clustered around the haem and axial ligands. |
