Protein engineering of detergent α-amylases

Abstract

We have developed large-scale production of alkaline cellulases, alkaline proteases, and alkaline α-amylases, and the enzymes have been incorporated into heavy-duty compact detergents and/or bleaches. The problem with traditional detergent enzymes is that they are seriously inactivated by chemical oxidants and chelating reagents, and these enzymes are thermally unstable, especially when they are used in automatic dishwashers. We have found an alkaline liquefying α-amylase AmyK (formerly designated LAMY) from alkaliphilic Bacillus sp. strain KSM-1378. AmyK is highly active at alkaline pH, compared with other industrial α-amylases reported so far, and resistant to various surfactants. However, AmyK is less thermostable than the Bacillus licheniformis α-amylase (BLA), therefore, improvement in the thermostability of AmyK is desirable for use at high temperatures under alkaline conditions in automatic dishwashers. Moreover, AmyK and other Bacillus α-amylases are inactivated by chemical oxidants. We tried to improve the oxidative stability of AmyK by replacing a Met residue with non-oxidizable amino acids as in the case of alkaline proteases that acquired oxidative stability by site-directed mutagenesis. In this article, we describe the properties and deduced amino acid sequence of AmyK, and improvement in thermostability and oxidative stability of the enzyme by site-directed mutagenesis.