INCREASING THERMAL-STABILITY OF SUBTILISIN FROM MUTATIONS SUGGESTED BY STRONGLY INTERACTING SIDE-CHAIN CLUSTERS

In this paper we present for seven subtilisin structures a systematic comparison of densely packed side-group dusters (defined as an ensembl e of side chains with extensive internal atomic contacts as compared w ith those made with the surrounding protein environment and measured r elative to the maximum possible for each residue type). Spatially cons istent clusters are observed at structurally equivalent positions in t he proteins, as revealed by careful multiple superpositioning of the r espective backbone atoms. The clusters are positioned at strategic loo p-connecting sites near the protein surfaces, The residues within cons istent dusters displaying extensive association show varying conservat ion at structurally equivalent alignment sites. Suggestions for residu e substitutions, as observed over the seven tertiary structures, were taken from the cluster positions and were shown to be consistent with a number of point mutations in one of the seven structures (savinase) that result in increased thermal Stability.