Mutations to alter Aspergillus awamori glucoamylase selectivity. IV. Combinations of Asn20-->Cys/Ala27-->Cys, Ser30-->Pro, Gly137-->Ala, 311-4 loop, Ser411-->Ala and Ser436-->Pro.

Six previously constructed and nine newly constructed Aspergillus awamori glucoamylases with multiple mutations made by combining existing single mutations were tested for their ability to produce glucose from maltodextrins. Multiple mutations have cumulative effects on glucose yield, specific activity and thermostability. No general correlation between glucose yield and thermostability was observed, although mutations that presumably impede unfolding at high temperatures uniformly increase thermostability and generally increase glucose yield. Peak glucose yields decrease with increasing temperature. The best combination of high glucose yield, high specific activity and high thermostability occurs in Asn20-->Cys/Ala27-->Cys/Ser30-->Pro/Gly137-->Ala glucoamylase.