Adaptation of class-13 alpha-amylases to diverse living conditions.

There are currently 35 available nonredundant molecular structures of class-13 alpha-amylases (EC 3.2.1.1), mostly from microbial organisms living under a wide range of environmental conditions. One of the most recent additions has been the first alpha-amylase structure of a hyperthermophilic archaeon [Linden et al., J. Biol. Chem. 2003, 278, 9875-9884]. The structure has been used for comparative analyses with a representative set of three alpha-amylases from thermophilic, mesophilic and psychrophilic sources to identify molecular parameters for environmental adaptation. Our analysis supports generally observed trends such as an increase in structural compactness as well as an increase in salt bridges in order to cope with high-temperature conditions. The two representative thermophilic structures used in this comparative study have independently evolved di-metal centres--not present in the mesophilic and psychrophilic structures--in the vicinity of the active site. These observations may provide impetus for the design of alpha-amylases with improved molecular properties to enhance their utility in biotechnological processes.