title: A novel two domain-fusion protein in cyanobacteria with similarity to the CAB/ELIP/HLIP superfamily: evolutionary implications and regulation.
abstract: Vascular plants contain abundant, light-harvesting complexes in the thylakoid membrane that are non-covalently associated with chlorophylls and carotenoids. These light-harvesting chlorophyll a/b binding (LHC) proteins are members of an extended CAB/ELIP/HLIP superfamily of distantly related polypeptides, which have between one and four transmembrane helices (TMH). This superfamily includes the single TMH, high-light-inducible proteins (Hlips), found in cyanobacteria that are induced by various stress conditions, including high light, and are considered ancestral to the LHC proteins. The roles of, and evolutionary relationships between, these superfamily members are of particular interest, since they function in both light harvesting and photoprotection and may have evolved through tandem gene duplication and fusion events. We have investigated the Hlips (hli gene family) in the thermophilic unicellular cyanobacterium Synechococcus OS-B'. The five hli genes present on the genome of Synechococcus OS-B' are relatively similar, but transcript analyses indicate that there are different patterns of transcript accumulation when the cells are exposed to various growth conditions, suggesting that different Hlips may have specific functions. Hlip5 has an additional TMH at the N-terminus as a result of a novel fusion event. This additional TMH is very similar to a conserved hypothetical, single membrane-spanning polypeptide present in most cyanobacteria. The evolutionary significance of these results is discussed.
authors.affiliation: Department of Plant Biology, The Carnegie Institution, Stanford, CA 94305, USA.
authors.forename: Oliver
authors.initials: O
authors.lastname: Kilian
authors.forename: Anne Soisig
authors.initials: AS
authors.lastname: Steunou
authors.forename: Arthur R
authors.initials: AR
authors.lastname: Grossman
authors.forename: Devaki
authors.initials: D
authors.lastname: Bhaya
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D019755:Carbon-Carbon Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002734:Chlorophyll / Q000096:biosynthesis; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D045342:Light-Harvesting Protein Complexes / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D016133:Polymerase Chain Reaction / Q000379:methods; D012329:RNA, Bacterial / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D046940:Synechococcus / Q000235:genetics*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D012329:RNA, Bacterial; C091582:high light-inducible protein, cyanobacteria; D002734:Chlorophyll; D019755:Carbon-Carbon Lyases; C052986:o-succinylbenzoic acid synthase