Directed coevolution of stability and catalytic activity in calcium-free subtilisin.

We have coevolved high activity and hyperstability in subtilisin by sequentially randomizing 12 amino acid positions in calcium-free subtilisin. The optimal amino acid for each randomized site was chosen based on stability and catalytic properties and became the parent clone for the next round of mutagenesis. Together, the 12 selected mutations increased the half-life of calcium-free subtilisin at elevated temperature by 15,000-fold.

Structural basis of thermostability. Analysis of stabilizing mutations in subtilisin BPN'.

The crystal structures of two thermally stabilized subtilisin BPN' variants, S63 and S88, are reported here at 1.8 and 1.9 A resolution, respectively.