Cytochrome f

Apocytochr_F_C
cytochrome f from the b6f complex of Phormidium laminosum
Identifiers
Symbol	Apocytochr_F_C
Pfam	PF01333
Pfam clan	CL0105
InterPro	IPR002325
PROSITE	PDOC00169
SCOP2	1ctm / SCOPe / SUPFAM
TCDB	3.D.3
OPM superfamily	92
OPM protein	3h1j
Available protein structures: PDB   IPR002325 PF01333 (ECOD; PDBsum)   AlphaFold IPR002325 PF01333

Cytochrome f is the largest subunit of cytochrome b₆f complex (plastoquinol—plastocyanin reductase; EC 1.10.99.1). In its structure and functions, the cytochrome b6f complex bears extensive analogy to the cytochrome bc1 complex of mitochondria and photosynthetic purple bacteria. Cytochrome f (cyt f) plays a role analogous to that of cytochrome c1, in spite of their different structures.¹

The 3D structure of Brassica rapa (Turnip) cyt f has been determined.² The lumen-side segment of cyt f includes two structural domains: a small one above a larger one that, in turn, is on top of the attachment to the membrane domain. The large domain consists of an anti-parallel beta-sandwich and a short haem-binding peptide, which form a three-layer structure. The small domain is inserted between beta-strands F and G of the large domain and is an all-beta domain. The haem nestles between two short helices at the N terminus of cyt f. Within the second helix is the sequence motif for the c-type cytochromes, CxxCH (residues 21–25), which is covalently attached to the haem through thioether bonds to Cys-21 and Cys-24. His-25 is the fifth haem iron ligand. The sixth haem iron ligand is the alpha-amino group of Tyr-1 in the first helix.² Cyt f has an internal network of water molecules that may function as a proton wire.² The water chain appears to be a conserved feature of cyt f.