Structural determinants of the stability of thermolysin-like proteinases.

Thermolysin is a member of a family of homologous proteinases which differ in their resistance to thermally induced unfolding and subsequent autolytic degradation. Site-directed mutagenesis studies of the thermolysin-like proteinase (TLP) from Bacillus stearothermophilus (TLP-ste) show that its reduced resistance to thermally induced autolysis, as compared to thermolysin, is due to only some of the 44 naturally occurring amino-acid differences between them. In fact TLP-ste becomes more resistant than thermolysin by mutation of just a few of these amino-acids. The crucial differences are all localized to a solvent-exposed region in the N-terminal domain of TLP-ste.