title: Photochromic biliproteins from the cyanobacterium Anabaena sp. PCC 7120: lyase activities, chromophore exchange, and photochromism in phytochrome AphA.
abstract: Photochromic biliproteins can be switched by light between two states, initiated by Z/E photoisomerization of the linear tetrapyrrole chromophore. The cyanobacterium Anabaena sp. PCC 7120 contains three genes coding for such biliproteins, two coding for phytochromes (aphA/B) and one for the alpha subunit of phycoerythrocyanin (pecA). (a) aphA was overexpressed in Escherichia coli with N-terminal His and S tags, and the protein was reconstituted by an optimized protocol with phycocyanobilin (PCB), to yield the photochromic chromoprotein, PCB-AphA, carrying the PCB chromophore. (b) AphA chromophorylation is autocatalytic such as in other phytochromes. (c) AphA chromophorylation is also possible by chromophore transfer from the PCB-carrying biliprotein, phycocyanin (CPC). The autocatalytic transfer is very slow, and it is enhanced more than 100-fold by catalysis of PCB:CpcA lyase and alpha-CPC as donor. (d) Through deletion mutations of aphA, a short sequence IQPHGV [amino acids (aa) 26-31] was found essential for the lyase activity of AphA, indicating an interaction of the N terminus with the chromophore-binding domain around cysteine 259. (e) A motif of at least 23 aa, starting with this sequence and located approximately 250 aa N terminal of the chromophore-binding cysteine, is proposed to relate to the lyase function in plant and most prokaryotic phytochromes. (f) Long-range interactions in AphA are further supported by blue-shifted absorptions (<or=12 nm) of both the Pr and Pfr forms of truncated chromoproteins.
authors.affiliation: College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, Hubei, People's Republic of China. kaihongzhao@ 163.com
authors.forename: Kai-Hong
authors.initials: KH
authors.lastname: Zhao
authors.forename: Yong
authors.initials: Y
authors.lastname: Ran
authors.forename: Mei
authors.initials: M
authors.lastname: Li
authors.forename: Ya-Nan
authors.initials: YN
authors.lastname: Sun
authors.forename: Ming
authors.initials: M
authors.lastname: Zhou
authors.forename: Max
authors.initials: M
authors.lastname: Storf
authors.forename: Michaela
authors.initials: M
authors.lastname: Kupka
authors.forename: Stefan
authors.initials: S
authors.lastname: Böhm
authors.forename: Claudia
authors.initials: C
authors.lastname: Bubenzer
authors.forename: Hugo
authors.initials: H
authors.lastname: Scheer
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017033:Anabaena / Q000201:enzymology* / Q000235:genetics; D001059:Apoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics; D008190:Lyases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D052980:Phycobilins; D010798:Phycocyanin / Q000737:chemistry* / Q000378:metabolism; D010834:Phytochrome / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D011758:Pyrroles / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D045725:Tetrapyrroles
chemical_list: D001059:Apoproteins; D001426:Bacterial Proteins; D010446:Peptide Fragments; D052980:Phycobilins; D021122:Protein Subunits; D011758:Pyrroles; D045725:Tetrapyrroles; C038397:phycoerythrocyanin; D010798:Phycocyanin; D010834:Phytochrome; C011069:phycocyanobilin; D008190:Lyases