short communications
The carboxylate atoms of the two catalytic aspartic acid residues in aspartic proteases are nearly coplanar and in the uncomplexed form share an in-plane nucleophilic water molecule that is central to the mechanism of these enzymes. This note reports that while reviewing the electron-density maps derived from the deposited data for uncomplexed plasmepsin II from Plasmodium falciparum [Asojo et al. (2003), J. Mol. Biol. 327, 173-181; PDB code 1lf4
], it was discovered that the aspartic acid residues in this structure should in fact be distinctly noncoplanar. The crystallographic model from the deposited coordinates has been re-refined against the 1.9 Å resolution published diffraction data to an Rcryst of 21.2% and an Rfree of 22.2%. The catalytic water molecule is present, but the plane of the carboxylate group of Asp214 is rotated by 66° from its original position.