PROTEIN STABILIZATION BY HYDROPHOBIC INTERACTIONS AT THE SURFACE

The contribution of the solvent-exposed residue 63 to thermal stabilit y of the thermolysin-like neutral protease of Bacillus stearothermophi lus was studied by analyzing the effect of twelve different amino acid substitutions at this position. The thermal stability of the enzyme w as increased considerably by introducing Arg, Lys or bulky hydrophobic amino acids. In general, the effects of the mutations showed that hyd rophobic contacts in this surface-located region of the protein are a major determinant of thermal stability. This observation contrasts wit h general concepts concerning the contribution of surface-located resi dues and surface hydrophobicity to protein stability and indicates new ways for protein stabilization by site-directed mutagenesis.