title: Cytochrome b561 protein family: expanding roles and versatile transmembrane electron transfer abilities as predicted by a new classification system and protein sequence motif analyses.
abstract: Cytochrome b561 family was characterized by the presence of "b561 core domain" that forms a transmembrane four helix bundle containing four totally conserved His residues, which might coordinate two heme b groups. We conducted BLAST and PSI-BLAST searches to obtain insights on structure and functions of this protein family. Analyses with CLUSTAL W on b561 sequences from various organisms showed that the members could be classified into 7 subfamilies based on characteristic motifs; groups A (animals/neuroendocrine), B (plants), C (insects), D (fungi), E (animals/TSF), F (plants+DoH), and G (SDR2). In group A, both motif 1, {FN(X)HP(X)2M(X)2G(X)5G(X)ALLVYR}, and motif 2, {YSLHSW(X)G}, were identified. These two motifs were also conserved in group B. There was no significant features characteristic to groups C and D. A modified version of motif 1, {LFSWHP(X)2M(X)3F(X)3M(X)EAIL(X)SP(X)2SS}, was found in group E with a high degree of conservation. Both motif 3, {DP(X)WFY(L)H(X)3Q}, and motif 4, {K(X)R(X)YWN(X)YHH(X)2G(R/Y)} ,were found in group F at different regions from those of motifs 1 and 2. The "DoH" domain common to the NH2-terminal region of dopamine beta-hydroxylase was found to form fusion proteins with the b561 core domains in groups F and G. Based on these results, we proposed a hypothesis regarding structures and functions of the 7 subfamilies of cytochrome b561.
authors.affiliation: Department of Molecular Science and Material Engineering, Graduate School of Science and Technology, Kobe University, Rokkodai-cho 1-1, Kobe, Hyogo 678-1297, Japan. mtsubaki@kobe-u.ac.jp
authors.forename: Motonari
authors.initials: M
authors.lastname: Tsubaki
authors.forename: Fusako
authors.initials: F
authors.lastname: Takeuchi
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Nakanishi
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000737:chemistry*; D003573:Cytochrome b Group / Q000737:chemistry* / Q000145:classification; D004579:Electron Transport; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D014364:Tryptophan / Q000737:chemistry
chemical_list: D029681:Arabidopsis Proteins; D003573:Cytochrome b Group; D020033:Protein Isoforms; C023646:cytochrome b561; D014364:Tryptophan