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AmyUS100DeltaIG is a variant of the most thermoactive and thermostable maltohexaose forming alpha-amylase produced by Geobacillus stearothermophilus sp.US100. This enzyme which was designed to improve the thermostability of the wild-type enzyme has acquired a very high resistance to chelator agents. According to modeling structural studies and with the aim of enhancing its resistance towards chemical oxidation, a mutant (AmyUS100DeltaIG/M197A) was created by substituting methionine 197 to alanine. The catalytic proprieties of the resulting mutant show alterations in the specific activity and the profile of starch hydrolysis. Interestingly, AmyUS100DeltaIG/M197A displayed the highest resistance to oxidation compared to the AmyUS100DeltaIG and to Termamyl300, the well-known commercial amylase used in detergent. Further, performance of the engineered alpha-amylase was estimated in the presence of commonly used detergent compounds and a wide range of commercial detergent (liquid and solid). These studies indicated a high compatibility and performance of AmyUS100DeltaIG/M197A, suggesting its potential application in detergent industry.

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The implications of Asn315 and Val450 in the atypical starch hydrolysis profile of Bacillus stearothermophilus Amy (a-amylase) US100 have been suggested previously [Ben Ali, Mhiri, Mezghani and Bejar (2001) Enzyme Microb. Tech. 28, 537-542]. In order to confirm this hypothesis, three mutants were generated. Of these two have a single mutation, N315D or V450G, whereas the third contains both mutations. Analysis of the starch breakdown-profile of these three mutants, as well as of the wild-type, allowed us to conclude that each single mutation induces a small variation in the hydrolysis product. However, the major end product produced by the double mutant shifts from maltopentaose/maltohexaose to maltose/maltotriose, confirming the involvement of these two residues in starch hydrolysis. The superimposition of AmyUS100 model with that of Bacillus licheniformis shows in AmyUS100 an additional loop containing residues Ile214 and Gly215. Remarkably, the deletion of these two residues increases the half-life at 100 degrees C from 15 min to approx. 70 min. Moreover, this engineered amylase requires less calcium, 25 p.p.m. instead of 100 p.p.m., to reach maximal thermostability.