Cytochrome b

From Wikipedia, the free encyclopedia
Jump to: navigation, search
1l0l opm.gif
Identifiers
Symbol Cytochrom_B_N
Pfam PF00033
InterPro IPR005797
PROSITE PDOC00171
SCOP 3bcc
SUPERFAMILY 3bcc
TCDB 3.D.3
OPM superfamily 3
OPM protein 3h1j
CDD cd00284

Cytochrome b is the main subunit of transmembrane cytochrome bc1 and b6f complexes.[1][2]

Function[edit]

In the mitochondrion of eukaryotes and in aerobic prokaryotes, cytochrome b is a component of respiratory chain complex III (EC 1.10.2.2) - also known as the bc1 complex or ubiquinol-cytochrome c reductase. In plant chloroplasts and cyanobacteria, there is an analogous protein, cytochrome b6, a component of the plastoquinone-plastocyanin reductase (EC 1.10.99.1), also known as the b6f complex. These complexes are involved in electron transport, pumping of protons to the create a PMF. The proton gradient is finally used for the generation of ATP. Concluding, the complexes play a vital part in cells.[3]

Structure[edit]

Cytochrome b/b6[4][5] is an integral membrane protein of approximately 400 amino acid residues that probably has 8 transmembrane segments. In plants and cyanobacteria, cytochrome b6 consists of two subunits encoded by the petB and petD genes. Cytochrome b/b6 non-covalently binds two heme groups, known as b562 and b566. Four conserved histidine residues are postulated to be the ligands of the iron atoms of these two heme groups.

Use in phylogenetics[edit]

Cytochrome b is commonly used as a region of mitochondrial DNA to determine phylogenetic relationships between organisms due to its sequence variability. It is considered to be most useful in determining relationships within families and genera. Comparative studies involving cytochrome b have resulted in new classification schemes and have been used to assign newly described species to a genus, as well as deepen the understanding of evolutionary relationships.[6]

Clinical significance[edit]

Mutations in cytochrome b primarily result in exercise intolerance in human patients; though more rare, severe multi-system pathologies have also been reported.[7]

Single-point mutations in cytochrome b of Plasmodium falciparum and P. berghei are associated with resistance to the anti-malarial drug atovaquone.[8]

Human genes[edit]

Human genes encoding cytochrome b proteins include:

  • CYB5A – cytochrome b5 type A (microsomal)
  • CYB5B – cytochrome b5 type B (outer mitochondrial membrane)
  • CYBASC3 – cytochrome b, ascorbate dependent 3
  • MT-CYB – mitochondrially encoded cytochrome b

References[edit]

  1. ^ Howell N (August 1989). "Evolutionary conservation of protein regions in the protonmotive cytochrome b and their possible roles in redox catalysis". J. Mol. Evol. 29 (2): 157–69. doi:10.1007/BF02100114. PMID 2509716. 
  2. ^ Esposti MD, De Vries S, Crimi M, Ghelli A, Patarnello T, Meyer A (July 1993). "Mitochondrial cytochrome b: evolution and structure of the protein". Biochim. Biophys. Acta 1143 (3): 243–71. doi:10.1016/0005-2728(93)90197-N. PMID 8329437. 
  3. ^ Blankenship, Robert (2009). Molecular Mechanisms of Photosynthesis. Blackwell Publishing. pp. 124–132. 
  4. ^ Howell N (1989). "Evolutionary conservation of protein regions in the protonmotive cytochrome b and their possible roles in redox catalysis". J. Mol. Evol. 29 (2): 157–169. doi:10.1007/BF02100114. PMID 2509716. 
  5. ^ Esposti MD, Crimi M, Ghelli A, Patarnello T, Meyer A, De Vries S (1993). "Mitochondrial cytochrome b: evolution and structure of the protein". Biochim. Biophys. Acta 1143 (3): 243–271. doi:10.1016/0005-2728(93)90197-N. PMID 8329437. 
  6. ^ Castresana, J. (2001). "Cytochrome b Phylogeny and the Taxonomy of Great Apes and Mammals". Molecular Biology and Evolution 18 (4): 465–471. PMID 11264397. 
  7. ^ Blakely EL, Mitchell AL, Fisher N, Meunier B, Nijtmans LG, Schaefer AM, Jackson MJ, Turnbull DM, Taylor RW (July 2005). "A mitochondrial cytochrome b mutation causing severe respiratory chain enzyme deficiency in humans and yeast". FEBS J. 272 (14): 3583–92. doi:10.1111/j.1742-4658.2005.04779.x. PMID 16008558. 
  8. ^ Siregar JE, Syafruddin D, Matsuoka H, Kita K, Marzuki S (June 2008). "Mutation underlying resistance of Plasmodium berghei to atovaquone in the quinone binding domain 2 (Qo(2)) of the cytochrome b gene". Parasitology International 57 (2): 229–32. doi:10.1016/j.parint.2007.12.002. PMID 18248769. 

External links[edit]