Molecular replacement studies on crystal structure of allophycocyanin fromred algae Porphyra yezoensis

Using the crystal structure of allophycocyanin from cyanobacterium Spirulin a platensis (APC-SP) as a search model, the crystal structure of allophycoc yanin from red algae Porphyra yezoensis (APC-PY) has been studied by molecu lar replacement methods. The APC-PY crystals (Form 3) belong to the space g roup of R32, cell dimensions a = b = 10.53 nm, c = 18.94 nm, alpha = beta = 90 degrees, gamma = 120 degrees; there is one alpha beta monomer in each c rystallographic asymmetric unit in the cell. The translation function searc h gave a unique peak with a correlation coefficient (Cc) of 67.0% and an R- factor of 36.1% for reflection data from 1.0 to 0.4 nm, Using the results b y molecular replacement, the initial model of APC-PY was built, and the coi ncidence of the chromophore in APC-PY initial model with its 2F(o)-F-c OMIT map further confirms the results by molecular replacement.