• Prosthetic group features
• Cytochromes f in motif databases
• Cytochromes f in alignment databases
• Cytochromes f in 3­D databases
• References

Haem type	Haem iron coordination	Axial iron ligands	Formal iron oxidation/spin states
Haem c	Hexacoordinate	NHis; NTyr	FeII (S=0); FeIII (S=1/2)

The cytochrome b₆f (cyt b₆f) integral membrane protein complex transfers electrons between the two reaction center complexes of oxygenic photosynthetic membranes, and participates in formation of the transmembrane electrochemical proton gradient by also transferring protons from the stromal to the internal lumen compartment [1]. The cyt b₆f complex contains four polypeptides: cyt f (285 aa), cyt b₆ (215 aa), Rieske iron-sulphur protein (179 aa), and subunit IV (160 aa) [2]. In its structure and functions, the cyt b₆f complex bears extensive analogy to the cyt bc₁ complex of mitochondria and photosynthetic purple bacteria; cyt f plays a role analogous to that of cyt c₁, in spite of their different structures [3].

The 3­D structure of turnip cyt f has been determined [4]. The lumen­side segment of cyt f includes two structural domains: a small one above a larger one which, in turn, is on top of the attachment to the membrane domain. The large domain consists of an antiparallel ß­sandwich and a short haem­binding peptide, which form a three­layer structure. The small domain is inserted between ß­strands F and G of the large domain and is an all­ß domain (Figure 1CTM a).

The haem nestles between two short helices at the N­terminus of cyt f. Within the second helix is the sequence motif for the c­type cytochromes:

CxxCH

Cyt f has an internal network of water molecules. It has been hypothesised that this water chain functions as a proton wire [4]. The water chain appears to be a conserved feature of cyt f.

Cytochrome f in motif databases

PRINTS ID	PRINTS AC	PROSITE/BLOCKS ID	PROSITE AC	BLOCKS AC
CYTOCHROMEF	PR00610	CYTOCHROME_C	PS00190	BL00190

Cytochrome f in alignment databases

Protein Superfamily	Pfam	LPFC 3­D alignment
00017; cytochrome f	-	-

PDB	scop	BSM	RELI Base	Header	¹
1ctm	1ctm	1ctm	1ctm	Cytochrome f (lumen­side domain) (reduced); turnip (Brassica rapa)	MS5AC1
1hcz	1hcz	1hcz	1hcz	Cytochrome f (lumen­side domain) (reduced) (-35 °C); turnip (Brassica rapa)	-
2pcf	2pcf	2pcf	2pcf	Turnip cytochrome f complex with spinach plastocyanin	-

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

References

1. Cramer, W.A., Martinez, S.E., Furbacher, P., Huang, D. and Smith, J.L. (1994a) The cytochrome b₆f complex. Curr. Opin. Struct. Biol. 4, 536-544.
2. Cramer, W.A., Martinez, S.E., Huang, D., Tae, G.S., Everly, R.M., Heymann, J.B., Cheng, R.H., Baker, T.S. and Smith, J.L. (1994b) Structural aspects of the cytochrome b₆f complex; structure of the lumen­side domain of cytochrome f. J. Bioenerg. Biomembr. 26, 31-47.
3. Prince, R.C. and George, G.N. (1995) Cytochrome f revealed. Trends Biochem. Sci. 20, 217-218.
4. Martinez, S.E., Huang, D., Ponomarev, M., Cramer, W.A. and Smith, J.L. (1996) The heme redox center of chloroplast cytochrome f is linked to a buried five­water chain. Protein Science 5, 1081-1092.

Bibliography on structural studies of cytochrome f