title: Crystal structure of allophycocyanin from red algae Porphyra yezoensis at 2.2-A resolution.
abstract: The crystal structure of allophycocyanin from red algae Porphyra yezoensis (APC-PY) at 2.2-A resolution has been determined by the molecular replacement method. The crystal belongs to space group R32 with cell parameters a = b = 105.3 A, c = 189.4 A, alpha = beta = 90 degrees, gamma = 120 degrees. After several cycles of refinement using program X-PLOR and model building based on the electron density map, the crystallographic R-factor converged to 19.3% (R-free factor is 26.9%) in the range of 10.0 to 2.2 A. The r.m.s. deviations of bond length and angles are 0.015 A and 2.9 degrees, respectively. In the crystal, two APC-PY trimers associate face to face into a hexamer. The assembly of two trimers within the hexamer is similar to that of C-phycocyanin (C-PC) and R-phycoerythrin (R-PE) hexamers, but the assembly tightness of the two trimers to the hexamer is not so high as that in C-PC and R-PE hexamers. The chromophore-protein interactions and possible pathway of energy transfer were discussed. Phycocyanobilin 1alpha84 of APC-PY forms 5 hydrogen bonds with 3 residues in subunit 2beta of another monomer. In R-PE and C-PC, chromophore 1alpha84 only forms 1 hydrogen bond with 2beta77 residue in subunit 2beta. This result may support and explain great spectrum difference exists between APC trimer and monomer.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China.
authors.forename: J Y
authors.initials: JY
authors.lastname: Liu
authors.forename: T
authors.initials: T
authors.lastname: Jiang
authors.forename: J P
authors.initials: JP
authors.lastname: Zhang
authors.forename: D C
authors.initials: DC
authors.lastname: Liang
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry; D003198:Computer Simulation; D016384:Consensus Sequence; D018360:Crystallography, X-Ray; D004735:Energy Transfer; D045342:Light-Harvesting Protein Complexes; D008958:Models, Molecular; D008969:Molecular Sequence Data; D052980:Phycobilins; D010798:Phycocyanin / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry*; D015203:Reproducibility of Results; D000461:Rhodophyta / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D045725:Tetrapyrroles
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D052980:Phycobilins; D010940:Plant Proteins; D011758:Pyrroles; D045725:Tetrapyrroles; C002497:allophycocyanin; D010798:Phycocyanin; C011069:phycocyanobilin