• Prosthetic group features
• Class II cytochromes c in motif databases
• Class II cytochromes c in alignment databases
• Class II cytochromes c in 3­D databases
• References

Class	Haem type	Haem iron coordination	Axial iron ligands	Formal iron oxidation/spin states
IIa	Haem c	Pentacoordinate	NHis	FeII (S=2); FeIII (S=3/2, 5/2)
		Hexacoordinate	NHis; CO, NO, CN¯ or other ligand	FeII (S=0); FeIII (S=1/2)
IIb		Hexacoordinate	NHis; SMet	FeII (S=0); FeIII (S=1/2)

Cytochromes c (cyt c) can be defined as electron­transfer proteins having one or several haem c groups, bound to the protein by one or, more commonly two, thioether bonds involving sulphydryl groups of cysteine residues. The fifth haem iron ligand is always provided by a histidine residue. Cyt c possess a wide range of properties and function in a large number of different redox processes [1].

Ambler [2] recognised four classes of cyt c. Class II includes the high­spin cyt c' and a number of low­spin cytochromes, e.g. cyt c­556. The haem­attachment site is close to the C­terminus. The cyt c' are capable of binding such ligands as CO, NO or CN¯ although with rate and equilibrium constants which are 10² to 10⁶­fold smaller than other high­spin hemoproteins [3]; this, coupled with its relatively low redox potential, makes it unlikely that cyt c' is a terminal oxidase. Therefore cyt c' probably functions as an electron transfer protein [4].

3­D structures of a number of cyt c' have been determined. The molecule usually exists as a dimer, with each monomer folding as a four­­helix bundle incorporating a covalently bound haem group at the core [4] (Figure 1BBH). The Chromatium vinosum cyt c' exhibits dimer dissociation upon ligand binding [5].

Class II cytochromes c in motif databases

PRINTS ID	PRINTS AC	PROSITE/BLOCKS ID	PROSITE AC	BLOCKS AC
CYTCHROMECII	PR00608	CYTOCHROME_C	PS00190	BL00190

Class II cytochromes c in alignment databases

Protein Superfamily	Pfam	LPFC 3­D alignment
00016; cytochrome c'	-	-

PDB	scop	BSM	RELI Base	Header	¹
1a7v	-	1a7v	-	Cytochrome c'; Rhodopseudomonas palustris	-
1bbh	1bbh	1bbh	1bbh	Cytochrome c'; Chromatium vinosum	MMS94080
1cgn	1cgn	1cgn	1cgn	Cytochrome c'; Alcaligenes denitrificans	-
1cgo	1cgo	1cgo	1cgo	Cytochrome c'; Alcaligenes sp.	-
1cpq	1cpq	1cpq	1cpq	Cytochrome c'; Rhodobacter capsulatus (Rhodopseudomonas capsulata)	-
1cpr	1cpr	1cpr	1cpr	Cytochrome c' (complex with Zn2+); Rhodobacter capsulatus (Rhodopseudomonas capsulata), strain St. Louis	-
1jaf	-	1jaf	1jaf	Cytochrome c'; Rhodocyclus gelatinosus	-
1nbb	1nbb	1nbb	1nbb	Cytochrome c' (complex with N­butyl isocyanide); Rhodobacter capsulatus (Rhodopseudomonas capsulata)	-
1rcp	1rcp	1rcp	1rcp	Cytochrome c'; Rhodobacter capsulatus (Rhodopseudomonas capsulata)	-
2ccy	2ccy	2ccy	2ccy	Cytochrome c'; Rhodospirillum molischianum	-
-	-	-	-	Cytochrome c'; Rhodospirillum rubrum	MMS93079

¹ Macromolecular Structures abstract. Full text is available to BioMedNet Members

References

1. Pettigrew, G.W. and Moore, G.R. (1987) Cytochromes c. Biological Aspects. Springer­Verlag, Berlin - Heidelberg - New York.
2. Ambler, R.P. (1991) Sequence variability in bacterial cytochromes c. Biochim. Biophys. Acta 1058, 42-47.
3. Kassner, R.J. (1991) Ligand binding properties of cytochromes c'. Biochim. Biophys. Acta 1058, 8-12.
4. Moore, G.R. (1991) Bacterial 4­­helical bundle cytochromes. Biochim. Biophys. Acta 1058, 38-41.
5. Ren, Z., Meyer, T.E. and McRee, D.E. (1993) Atomic structure of a cytochrome c' with an unusual ligand­controlled dimer dissociation at 1.8 Å resolution. J. Mol. Biol. 234, 433-445.

Bibliography on structural studies of Class II cytochromes c