title: Crystallization of phycoerythrocyanin from the cyanobacterium Mastigocladus laminosus and preliminary characterization of two crystal forms.
abstract: The light-harvesting protein phycoerythrocyanin from the cyanobacterium Mastigocladus laminosus Cohn has been crystallized in two different crystal forms by vapour diffusion. In 5% (w/v) polyethylene glycol at pH 8.5, hexagonal crystals of space group P63 with cell constants a = b = 158 A, c = 40.6 A were obtained, which turned out to be almost isomorphous with the hexagonal crystals of C-phycocyanin from the same organism. Consequently, the conformation of both phycobiliproteins must be very similar. From 1.5 M-ammonium sulfate (pH 8.5), orthorhombic crystals of space group P2221 with cell constants a = 60.5 A, b = 105 A, c = 188 A could be grown. Density measurements of these crystals indicate that the unit cell contains 18 (alpha beta)-units. A detailed packing scheme is proposed that is consistent with the observed pseudo-hexagonal X-ray intensity pattern and with the known size and shape of (alpha beta)3-trimers of C-phycocyanin. Accordingly, disc-like (alpha beta)3-trimers are associated face-to-face and stacked one upon another in rods with a period of 60.5 A, corresponding to the cell dimension a.
mesh_terms: D003461:Crystallography; D000458:Cyanobacteria / Q000032:analysis*; D046911:Macromolecular Substances; D052980:Phycobilins; D010798:Phycocyanin; D010860:Pigments, Biological
chemical_list: D046911:Macromolecular Substances; D052980:Phycobilins; D010860:Pigments, Biological; C038397:phycoerythrocyanin; D010798:Phycocyanin