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485  structures 5406  species 20  interactions 25696  sequences 315  architectures

Family: Cytochrom_C (PF00034)

Summary: Cytochrome c

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This is the Wikipedia entry entitled "Cytochrome c family". More...

Cytochrome c family Edit Wikipedia article

Cytochrome c
PDB 1cry EBI.jpg
Structure of cytochrome c2 from Rhodopseudomonas viridis.[1]
Symbol Cytochrom_C
Pfam PF00034
InterPro IPR003088
SCOP 1cry
OPM superfamily 78
OPM protein 1hrc
Cytochrome C'
PDB 1bbh EBI.jpg
atomic structure of a cytochrome c' with an unusual ligand-controlled dimer dissociation at 1.8 angstroms resolution
Symbol Cytochrom_C_2
Pfam PF01322
InterPro IPR002321
SCOP 1cgo
Class III cytochrome C family
PDB 1h29 EBI.jpg
sulfate respiration in desulfovibrio vulgaris hildenborough: structure of the 16-heme cytochrome c hmca at 2.5 a resolution and a view of its role in transmembrane electron transfer
Symbol Cytochrom_CIII
Pfam PF02085
Pfam clan CL0317
InterPro IPR020942
SCOP 2cdv
CDD cd08168

Cytochromes c (cytC) are electron-transfer proteins having one or several heme c groups, bound to the protein by one or, more generally, two thioether bonds involving sulphydryl groups of cysteine residues. The fifth haem iron ligand is always provided by a histidine residue. Cytochromes c possess a wide range of properties and function in a large number of different redox processes.[2] The founding member of this family is mitochondrial cytochrome c.

Ambler[3] recognized 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 cytC 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 cytc-550, which have several extra loops by comparison with class IB cytC.
  • Class II includes the high-spin cytC' and a number of low-spin cytochromes, e.g. cyt c-556. The haem-attachment site is close to the C terminus. The cytC' are capable of binding such ligands as CO, NO or CN(-), albeit with rate and equilibrium constants 100 to 1,000,000-fold smaller than other high-spin haemoproteins.[4] This, coupled with its relatively low redox potential, makes it unlikely that cytC' is a terminal oxidase. Thus cytC' probably functions as an electron transfer protein.[5] The 3D structures of a number of cytC' have been determined. The molecule usually exists as a dimer, each monomer folding as a four-alpha-helix bundle incorporating a covalently-bound haem group at the core.[5] The Chromatium vinosum cytC' exhibits dimer dissociation upon ligand binding.[6]
  • Class III comprises the low redox potential multiple haem cytochromes: cyt C7 (trihaem), C3 (tetrahaem), and high-molecular-weight cytC, HMC (hexadecahaem), with only 30-40 residues per haem group. The haem c groups, all bis-histidinyl coordinated, are structurally and functionally nonequivalent and present different redox potentials in the range 0 to -400 mV.[7] The 3D structures of a number of cyt C3 proteins have been determined. The proteins consist of 4-5 alpha-helices and 2 beta-strands wrapped around a compact core of four non-parallel haems, which present a relatively high degree of exposure to the solvent. The overall protein architecture, haem plane orientations and iron-iron distances are highly conserved.[7]
  • Class IV includes complex proteins containing other prosthetic groups besides haem c, such as flavocytochromes c and cytochromes cd.[3]


Human proteins containing this domain



  1. ^ Miki K, Sogabe S, Uno A, et al. (May 1994). "Application of an automatic molecular-replacement procedure to crystal structure analysis of cytochrome c2 from Rhodopseudomonas viridis". Acta Crystallogr. D. 50 (Pt 3): 271–5. doi:10.1107/S0907444993013952. PMID 15299438. 
  2. ^ Moore GR, Pettigrew GW (1987). : –.  Missing or empty |title= (help)
  3. ^ a b Ambler RP (1991). "Sequence variability in bacterial cytochromes c". Biochim. Biophys. Acta. 1058 (1): 42–47. doi:10.1016/S0005-2728(05)80266-X. PMID 1646017. 
  4. ^ Kassner RJ (May 1991). "Ligand binding properties of cytochromes c'". Biochim. Biophys. Acta. 1058 (1): 8–12. doi:10.1016/s0005-2728(05)80257-9. PMID 1646027. 
  5. ^ a b Moore GR (May 1991). "Bacterial 4-alpha-helical bundle cytochromes". Biochim. Biophys. Acta. 1058 (1): 38–41. doi:10.1016/s0005-2728(05)80265-8. PMID 1646016. 
  6. ^ Ren Z, Meyer T, McRee DE (November 1993). "Atomic structure of a cytochrome c' with an unusual ligand-controlled dimer dissociation at 1.8 A resolution". J. Mol. Biol. 234 (2): 433–45. doi:10.1006/jmbi.1993.1597. PMID 8230224. 
  7. ^ a b Coutinho IB, Xavier AV (1994). "Tetraheme cytochromes". Meth. Enzymol. 243: 119–40. doi:10.1016/0076-6879(94)43011-X. PMID 7830606. 

This article incorporates text from the public domain Pfam and InterPro IPR002321

This article incorporates text from the public domain Pfam and InterPro IPR020942

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

Cytochrome c Provide feedback

The Pfam entry does not include all Prosite members. The cytochrome 556 and cytochrome c' families are not included. All these are now in a new clan together. The C-terminus of DUF989, PF06181 has now been merged into this family.

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This tab holds annotation information from the InterPro database.

InterPro entry IPR009056

After cytochrome c is synthesized in the cytoplasm as apocytochrome c, it is transported through the outer mitochondrial membrane to the intermembrane space, where haem is covalently attached by thioester bonds to two cysteine residues located in the cytochrome c centre. Cytochrome c is required during oxidative phosphorylation as an electron shuttle between Complex III (cytochrome c reductase) and IV (cytochrome c oxidase). In addition, cytochrome c is involved in apoptosis in more complex organisms such as Xenopus, rats and humans. Cellular stress can induce cytochrome c release from the mitochondrial membrane. In mammals, cytochrome c triggers the assembly of the apoptosome, consisting of cytochrome c, Apaf-1 and dATP, which activates caspase-9, leading to cell death [PUBMED:12729583, PUBMED:10707095]. There are several different members of the cytochrome c family with different functional roles, for instance cytochrome c549 is associated with photosystem II [PUBMED:11315568].

The known structures of c-type cytochromes have six different classes of fold. Of these, four are unique to c-type cytochromes [PUBMED:12594933, PUBMED:2166169]. The consensus sequence for the cytochrome c centre is Cys-X-X-Cys-His, where the histidine residue is one of the two axial ligands of the haem iron [PUBMED:10647174]. This arrangement is shared by all proteins known to belong to the cytochrome c family, which presently includes both mono-haem proteins and multi-haem proteins. This entry represents mono-haem cytochrome c proteins (excluding class II and f-type cytochromes), such as cytochromes c, c1, c2, c5, c555, c550 to c553, c556, and c6.

Cytochrome c-type centres are also found in the active sites of many enzymes, including cytochrome cd1-nitrite reductase as the N-terminal haem c domain, in quinoprotein alcohol dehydrogenase as the C-terminal domain, in Quinohemoprotein amine dehydrogenase A chain as domains 1 and 2, and in the cytochrome bc1 complex as the cytochrome bc1 domain.

Gene Ontology

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Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan Cytochrome-c (CL0318), which has the following description:

This family includes proteins where a covalently-bound haem completes the core. The core is three helices in an open folded leaf formation. The members are monodomain cytochromes.

The clan contains the following 13 members:

CCP_MauG Cytochrom_C Cytochrom_C1 Cytochrom_C550 Cytochrome-c551 Cytochrome_CBB3 Dehyd-heme_bind DHC DHOR DUF1924 FixO Haem_bd PSCyt1


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Curation and family details

This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.

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Seed source: Prosite
Previous IDs: cytochrome_c;
Type: Domain
Sequence Ontology: SO:0000417
Author: Bateman A , Sonnhammer ELL
Number in seed: 66
Number in full: 25696
Average length of the domain: 97.60 aa
Average identity of full alignment: 18 %
Average coverage of the sequence by the domain: 34.51 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 45638612 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 21.3 21.3
Trusted cut-off 21.3 21.3
Noise cut-off 21.2 21.2
Model length: 92
Family (HMM) version: 21
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Species distribution

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Colour assignments

Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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There are 20 interactions for this family. More...

PSII FCSD-flav_bind MHC_II_beta peroxidase Fer2 Cytochrom_C1 Pyr_redox_2 COX1 Cytochrom_C1 PsbJ COX2 CCP_MauG CCP_MauG Fe_hyd_SSU MHC_II_alpha Cytochrom_C Fer4 peroxidase PsbU WD40


For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Cytochrom_C domain has been found. There are 485 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.

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