Protein engineering for thermostabilisation of proteins: some theoretical rules and application to a β-glucanase

Protein thermostability has been investigated by two approaches. (A) Computational. To study the relationship between thermostability and conformational characteristics of proteins, 195 single amino acid residue replacements have been analysed for several protein conformational characteristics. From the analyses, some general rules arise which suggest where amino acid substitutions can be made to enhance protein thermostability. (B) Experimental. Glucohydrolases are biotechnologically important enzymes. We are analysing by site directed mutagenesis the structure/function relationship of two bacterial glucohydrolases, a 1,3-1,4-β-glucanase and a β-glucosidase. We have determined the key residues for catalysis and substrate binding, and redesigned the stability and specificity of the glucanase. A glucanase thermorresistant mutant (N57A) has been obtained.