Synthesis and assembly of the cytochrome b-f complex in higher plants

Abstract

The cytochrome b-f complex is composed of four polypeptide subunits, three of which, cytochrome f, cytochrome b-563 and subunit IV, are encoded in chloroplast DNA and synthesised within the chloroplast, and the fourth, the Rieske FeS protein, is encoded in nuclear DNA and synthesised in the cytoplasm. The assembly of the cytochrome b-f complex therefore requires the interaction of subunits encoded by different genomes. A key role for the nuclear-encoded Rieske FeS protein in the assembly of the complex is suggested by a study of cytochrome b-f complex mutants. The assembly of individual subunits of the complex may be regulated by the availability of prosthetic groups. The genes for the chloroplast-encoded subunits and cDNA clones for the Rieske FeS protein have been isolated and characterised. Cytochrome f and the Rieske FeS protein are synthesised initially with N-terminal presequences required for their correct assembly within the chloroplast. The deduced amino acid sequences of the four subunits have been used to suggest models for the arrangement of the polypeptides in the thylakoid membrane.

Import and processing of the precursor of the Rieske FeS protein of tobacco chloroplasts

“…bic residues near the N-terminus, and highly conserved regions containing cysteine and histidine residues near the C-terminus [28,29,31,36]. The hydrophobic residues are proposed to hold the protein in the thylakoid membrane by forming one or two transmembrane e-helices [ 36,39]. The topology of the polypeptide chain in the membrane has not yet been established [39].…”

Functional Characterization of Chlamydomonas Mutants Defective in Cytochrome f Maturation

“…The thylakoid processing peptidase (TPP), 1 homologous to the bacterial peptidase involved in the processing of secreted proteins (9), cleaves the presequence of cytochrome f right after a characteristic Ala-Gln-Ala motif. Tyrosine 32 thus becomes the N terminus of the mature protein (10,11). Mature cytochrome f remains anchored in the membrane by its C-terminal ␣-helix (11,12).…”

“…Tyrosine 32 thus becomes the N terminus of the mature protein (10,11). Mature cytochrome f remains anchored in the membrane by its C-terminal ␣-helix (11,12). The three-dimensional structure of the soluble part of cytochrome f revealed that the free amino group of the Nterminal tyrosine of the mature protein acts as sixth ligand to the c heme (13).…”

Cytochrome bc 1 and b 6 f complexes of photosynthetic membranes

“…Thus, for the mitochondrial cytochrome bc 1 complex, only the cytochrome b gene is found in the organelle genome and all the remaining subunits are nuclear-encoded (Nobrega and Tzagoloff 1980). In the case of the chloroplast cytochrome b6f complex, three of the subunits, cytochrome f, cytochrome b 6 and subunit IV, are chloroplastencoded and the gene for the Rieske iron-sulfur protein is found in the nuclear genome (Willey and Gray 1988). The cytochrome b 6 and subunit IV genes are co-transcribed in chloroplasts but these two genes are not linked to the gene for cytochrome f. The latter is located in a different operon that is approximately 20 kb away from the petBD operon in the spinach chloroplast genome.…”