Subtilisin BPN' at 1.6 A 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 A 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, P2(1)2(1)2(1) and P2(1). 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.