“…This involved four steps: (1) engineering of highly stable and refoldable subtilisin (
11,
12), (2) modifications of binding pockets resulting in a strong preference for sequences of the form P4−P1 = YRAL (
13−
17), (3) selection of an independently stable prodomain with high affinity for subtilisin (
18,
19), and (4) engineering a tunable active site by means of a D32A1 mutation which renders activity dependent on the presence of certain small anions such as fluoride and azide (
20−
22). The resulting switchable subtilisin, whose activity against cognate sequences (e.g., YRAL-) can be accelerated more than 3000-fold by 100 mM azide, is denoted S189.
1A shorthand for denoting amino acid substitutions employs the single-letter amino acid code as follows: N218S denotes the change of asparagine 218 to serine, and Δ75−83 denotes the deletion of residues 75−83 from the amino acid sequence.
…”