Starch-Binding Domain Affects Catalysis in Two Lactobacillus α-Amylases

Abstract

ABSTRACT A new starch-binding domain (SBD) was recently described in α-amylases from three lactobacilli ( Lactobacillus amylovorus , Lactobacillus plantarum , and Lactobacillus manihotivorans ). Usually, the SBD is formed by 100 amino acids, but the SBD sequences of the mentioned lactobacillus α-amylases consist of almost 500 amino acids that are organized in tandem repeats. The three lactobacillus amylase genes share more than 98% sequence identity. In spite of this identity, the SBD structures seem to be quite different. To investigate whether the observed differences in the SBDs have an effect on the hydrolytic capability of the enzymes, a kinetic study of L. amylovorus and L. plantarum amylases was developed, with both enzymes acting on several starch sources in granular and gelatinized forms. Results showed that the amylolytic capacities of these enzymes are quite different; the L. amylovorus α-amylase is, on average, 10 times more efficient than the L. plantarum enzyme in hydrolyzing all the tested polymeric starches, with only a minor difference in the adsorption capacities.