Crystallization of phycoerythrocyanin from the cyanobacterium Mastigocladus laminosus and preliminary characterization of two crystal forms |
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Authors: | R Rümbeli T Schirmer W Bode W Sidler H Zuber |
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Institution: | 1. Institut für Molekularbiologie und Biophysik. ETH-Hönggerberg, CH-8093 Zürich, Switzerland;2. Max-Planek-Institut für Biochemie. D-8033 Martinsried, Federal Republic of Germany |
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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. |
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