title: Crystal structure of a phycourobilin-containing phycoerythrin at 1.90-A resolution.
abstract: The structure of R-phycoerythrin (R-PE) from the red alga Griffithsia monilis was solved at 1.90-A resolution by molecular replacement, using the atomic coordinates of cyanobacterial phycocyanin from Fremyella diplosiphon as a model. The crystallographic R factor for the final model is 17.5% (Rfree 22.7%) for reflections in the range 100-1.90 A. The model consists of an (alphabeta)2 dimer with an internal noncrystallographic dyad and a fragment of the gamma-polypeptide. The alpha-polypeptide (164 amino acid residues) has two covalently bound phycoerythrobilins at positions alpha82 and alpha139. The beta-polypeptide (177 residues) has two phycoerythrobilins bound to residues beta82 and beta158 and one phycourobilin covalently attached to rings A and D at residues beta50 and beta61, respectively. The electron density of the gamma-polypeptide is mostly averaged out by threefold crystallographic symmetry, but a dipeptide (Gly-Tyr) and one single Tyr could be modeled. These two tyrosine residues of the gamma-polypeptide are in close proximity to the phycoerythrobilins at position beta82 of two symmetry-related beta-polypeptides and are related by the same noncrystallographic dyad as the (alphabeta)2 dimer. Possible energy transfer pathways are discussed briefly.
authors.affiliation: Institut für Biophysik und Strahlenbiologie, Universität Freiburg, Albertstrasse 23, Freiburg, D-79104, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Ritter
authors.forename: R G
authors.initials: RG
authors.lastname: Hiller
authors.forename: P M
authors.initials: PM
authors.lastname: Wrench
authors.forename: W
authors.initials: W
authors.lastname: Welte
authors.forename: K
authors.initials: K
authors.lastname: Diederichs
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D052980:Phycobilins; D010798:Phycocyanin / Q000737:chemistry; D010799:Phycoerythrin / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D000461:Rhodophyta; D014557:Urobilin / Q000031:analogs & derivatives
chemical_list: D052980:Phycobilins; D010798:Phycocyanin; D010799:Phycoerythrin; D014557:Urobilin; C044986:phycourobilin