Crystal structure of α-amylase from Oryza sativa: molecular insights into enzyme activity and thermostability

AmyI-1 is an alpha-amylase from Oryza sativa (rice) and plays a crucial role in degrading starch in various tissues and at various growth stages. This enzyme is a glycoprotein with an N-glycosylated carbohydrate chain, a unique characteristic among plant alpha-amylases. In this study, we report the first crystal structure of AmyI-1 at 2.2-angstrom resolution. The structure consists of a typical (beta/alpha)(8)-barrel, which is well-conserved among most alpha-amylases in the glycoside hydrolase family-13. Structural superimposition indicated small variations in the catalytic domain and carbohydrate-binding sites between AmyI-1 and barley alpha-amylases. By contrast, regions around the N-linked glycosylation sites displayed lower conservation of amino acid residues, including Asn-263, Asn-265, Thr-307, Asn-342, Pro-373, and Ala-374 in AmyI-1, which are not conserved in barley alpha-amylases, suggesting that these residues may contribute to the construction of the structure of glycosylated AmyI-1. These results increase the depths of our understanding of the biological functions of AmyI-1.