Molecular replacement studies on crystal structure of allophycocyanin from red algae Porphyra yezoensis

Using the crystal structure of allophycocyanin from cyanobacterium Spirulina platensis (APC-SP) as a search model,the crystal structure of allophycocyanin from red algae Porphyra yezoensis (APC-PY) has been studied by molecular replacement methods.The APC-PY crystals (Form 3) belong to the space group of R32,cell dimensions a=b= 10.53 nm,c=18.94 nm,α= β= 90°,γ=120°;there is one αβ monomer in each crystallographic asymmetric unit in the cell.The translation function search 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 by molecular replacement,the initial model of APC-PY was built,and the coincidence of the chromophore in APC-PY initial model with its 2Fo-Fc OMIT map further confirms the results by molecular replacement.