Designing proteins (Protein engineering)

In order to improve their properties for thermal and pH stability, solvent tolerance and solubility, catalytic potency etc. For example 

IMPROVING LAUNDRY DETERGENT ENZYME SUBTILISIN:

Subtilisin is a protease (a protein-digesting enzyme) initially obtained from Bacillus subtilis. The active site features a charge-relay network involving Asp-32, His-64, and active site Ser-221 arranged in a catalytic triad. Studies have implicated methionine 222 as a primary site for oxidative inactivation of subtilisin. Site-directed mutagenesis has been employed in the construction of subtilisin variants with improved storage and oxidation stabilities. Because of uncertainties in predicting which amino acid would be the optimal substitute for methionine 222, scientists have  prepared all 19 amino acid substitutions at this site in the cloned subtilisin gene. Mutant enzymes were expressed in Bacillus subtilis and were found to vary widely in specific activity. Mutants containing nonoxidizable amino acids (i.e. Ser, Ala) were resistant to inactivation, whereas methionine and cysteine enzymes were rapidly inactivated.