{PDOC00748} {PS00968; ANTENNA_COMP_ALPHA} {PS00969; ANTENNA_COMP_BETA} {BEGIN} ******************************************************** * Antenna complexes alpha and beta subunits signatures * ******************************************************** In photosynthetic bacteria the antenna complexes function as light-harvesting systems that absorb light radiation and transfer the excitation energy to the reaction centers. The antenna complexes are generally composed of two polypeptides (alpha and beta chains); two or three bacteriochlorophyll (BChl) molecules and some carotenoids [1,2]. Both the alpha and the beta chains of antenna complexes are small proteins of 42 to 68 residues which share a three-domain organization. They are composed of a N-terminal hydrophilic cytoplasmic domain followed by a transmembrane region and a C-terminal hydrophilic periplasmic domain. In the transmembrane region of both chains there is a conserved histidine which is most probably involved in the binding of the magnesium atom of a bacteriochlorophyll group. The beta chains contain an additional conserved histidine which is located at the C-terminal extremity of the cytoplasmic domain and which is also thought to be involved in bacteriochlorophyll-binding. We have developed signature patterns for the alpha and for the beta subunits. These signature patterns include the conserved histidine residues. -Consensus pattern: [LIVFAG]-x-[GASV]-[LIVFA]-x-[IV]-H-x(3)-[LIVM]-[GSTAE]- [STANH]-x(1,3)-[STN]-W-[LIVMFYW] [The H binds BChl] -Sequences known to belong to this class detected by the pattern: ALL alpha chains. -Other sequence(s) detected in Swiss-Prot: NONE. -Consensus pattern: [EQ]-x(4)-[HGQ]-x(5)-[GSTA]-x(3)-[FYV]-x(3)-[AG]-x(2)- [AV]-H-x(7)-P [The two H bind BChl] -Sequences known to belong to this class detected by the pattern: ALL beta chains, except for Ectothiorhodospira halochloris B800/830/1020 beta-2. -Other sequence(s) detected in Swiss-Prot: NONE. -Last update: December 2004 / Pattern and text revised. [ 1] Wagner-Huber R., Brunisholz R.A., Bissig I., Frank G., Suter F., Zuber H. Eur. J. Biochem. 205:917-925(1992). [ 2] Brunisholz R.A., Zuber H. "Structure, function and organization of antenna polypeptides and antenna complexes from the three families of Rhodospirillaneae." J. Photochem. Photobiol. B 15:113-140(1992). PubMed=1460542 -------------------------------------------------------------------------------- PROSITE is copyrighted by the SIB Swiss Institute of Bioinformatics and distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives (CC BY-NC-ND 4.0) License, see https://prosite.expasy.org/prosite_license.html -------------------------------------------------------------------------------- {END}