Isolation, crystallization, crystal structure analysis and refinement of B-phycoerythrin from the red alga Porphyridium sordidum at 2.2 A resolution.
The light-harvesting pigment-protein complex B-phycoerythrin from the red alga Porphyridium sordidum has been isolated and crystallized. B-Phycoerythrin consists of three different subunits forming an (alpha beta)6 gamma aggregate. The three-dimensional structure of the (alpha beta)6 hexamer was solved by Patterson search techniques using the molecular model of C-phycocyanin from Fremyella diplosiphon. The asymmetric unit of the crystal cell (space group P3, with a = b = 111.2 A, c = 59.9 A, alpha = beta = 90 degrees, gamma = 120 degrees) contains two (alpha beta) monomers related by a local dyad. Three asymmetric units are arranged around the crystallographic 3-fold axis building an (alpha beta)6 hexamer, as in C-phycocyanin. The crystal structure has been refined by energy-restrained crystallographic refinement and model building. The conventional R-factor of the final model was 18.9% with data to 2.2 A resolution. The molecular structures of the alpha and beta-subunits resemble those of C-phycocyanin. Major changes in comparison to phycocyanin are caused by deletion or insertion of segments involved in protein-chromophore interactions. The singly linked phycoerythrobilin chromophores alpha-84, alpha-140a, beta-84 and beta-155 are each covalently bound to a cysteine by ring A. The doubly linked chromophore beta-50/beta-61 is attached at cysteine beta-50 through ring A and at cysteine beta-61 through ring D. B-Phycoerythrin contains additionally a 30 kDa gamma-subunit, which is presumably located in the central cavity of the hexamer. It is disordered, as a consequence of crystal and local symmetry averaging.
Ficner
R
R
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Lobeck
K
K
Schmidt
G
G
Huber
R
R
D000595:Amino Acid Sequence; D004735:Energy Transfer; D008958:Models, Molecular; D008969:Molecular Sequence Data; D052980:Phycobilins; D010798:Phycocyanin / Q000737:chemistry; D010799:Phycoerythrin / Q000737:chemistry*; D011487:Protein Conformation; D011758:Pyrroles / Q000737:chemistry; D000461:Rhodophyta / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D013237:Stereoisomerism; D045725:Tetrapyrroles; D014961:X-Ray Diffraction
D052980:Phycobilins; D011758:Pyrroles; D045725:Tetrapyrroles; D010798:Phycocyanin; D010799:Phycoerythrin; C011069:phycocyanobilin