Determination of hemihedral twinning and initial structural analysis of crystals of the procarboxypeptidase A ternary complex

The initial structural analysis of the ternary complex of procarboxypeptidase A from hemihedrally twinned crystals diffracting up to 2.8 Å is described. Detection of twinning by different techniques is presented, including biochemical and intensity statistics approaches. The structure was initially solved using Patterson-search techniques, and the three positioned search models were used to effectively deconvolute the twinned data.