Sequence homology and structural similarity between cytochrome b of mitochondrial complex III and the chloroplast b6-f complex: position of the cytochrome b hemes in the membrane.

Abstract

Sequence homology and structural similarity between cytochrome b of mitochondrial complex III ABSTRACTThe amino acid sequences of cytochrome b of complex III from five different mitochondrial sources (human, bovine, mouse, yeast, and Aspergilus nidulans) and the chloroplast cytochrome b6 from spinach show a high degree of homology. Calculation of the distribution of hydrophobic residues with a "hydropathy" function that is conserved in this family of proteins implies that the membrane-folding pattern of the 42-kilodalton (kDa) mitochondrial cytochromes involves 8-9 membrane-spanning domains. The smaller 23-kDa chloroplast cytochrome appears to fold in five spanning domains that are similar to the first five of the mitochondria. Four highly conserved histidines are considered to be the likely ligands for the two hemes. The positions of the histidines along the spanning segments and in a cross section of the membrane-spanning a helices implies that two ligand pairs, His-82-His-

Phosphorylation of cytochrome b6 by the LHC II kinase associated with the cytochrome complex

“…Volume 298, number I FEBS LE-ITERS FebruaPy 1992 [13,14] hydrophilic loop of the N-terminal sequence, or, probably less likely, Thr-107 in the small central, and Ser-212 in the terminal stroma-located segments of the polypeptide chain. All these residues are remarkably conserved in the corresponding tobacco protein [lS].…”

DNA sequence analysis of diuron‐resistant mutations in the mitochondrial cytochrome b gene of Saccharomyces cerevisiae

“…The 17 kDa (subunit 4) protein of the chloroplast b,$ complex is homologous to the second half of the mitochondrial cytochrome b polypeptide [9]. The mutated amino acid phenylalanine no.225 is found at the appropriate position within the 17 kDa protein and is also conserved in cytochrome b isolated from Aspergilhs nidulans.…”

“…The position of each mutated amino acid has been indicated on a protein folding model of cytochrome b adapted from [9] (fig.2). On this basis, all mutations appeared to be located in hydrophilic segments of the protein and were located on either side of the membrane.…”

“…In addition to diu2, exon 1 carries three loci anal, mucl and myxl; exon 4 carries ana and funl; exon 5 This paper will be reported in part in the 4th EBEC Reports carries muc3 and exon 6 carries muc2 and myx2 ( fig.1). The wild type sequence of the yeast cytochrome b gene is known [8] and a hydropathy plot of the deduced amino acid sequence has been used to construct a protein folding model [9]. The identification of specific DNA sequence changes within the cytochrome b gene codons of drug-resistant mutants has recently become practical.…”

Heme binding properties of heterologously expressed spinach cytochrome b6: Implications for transmembrane b‐type cytochrome formation

“…Besides cytochrome b 559 0 , a transmembrane helix dimer which binds one heme [9], cytochrome b 6 represents another simple, yet initially studied transmembrane b-type cytochrome. The transmembrane four-helix bundle binds two heme cofactors noncovalently and the protein is homologous in its structure and function to the four N-terminal transmembrane helices of cytochrome b [10,11]. Many designed heme proteins are the soluble rendered counterparts of cytochrome b 6 [12,13].…”