Subtilisin BPN' at 1.6 Å Resolution: Analysis for Discrete Disorder and Comparison of Crystal Forms

The three-dimensional structure of the serine protease subtilisin BPN' (SBT) has been refined at 1.6 Å resolution in space group C2 to a final R value of 0.17. 17 regions of discrete disorder have been identified and analyzed. Two of these are dual-conformation peptide units; the remainder involve alternate rotamers of side chains either alone or in small clusters. The structure is compared with previously reported high-resolution models of SBT in two other space groups, P2₁2₁2₁ and P2₁. Apart from the surface, there are no significant variations in structure among the three crystal forms. Structural variations observed at the protein surface occur predominantly in regions of protein-protein contact. The crystal packing arrangements in the three space groups are compared.