A flexible loop controlling the enzymatic activity and specificity in a glycosyl hydrolase family 19 endochitinase from barley seeds (Hordeum vulgare L.).

To examine the role of the loop structure consisting of residues 70-82 (70-82 loop) localized to +3/4 subsite of the substrate binding cleft of a family GH-19 endochitinase from barley seeds, Trp72 and Trp82 were mutated, and the mutated enzymes (W72A, W82A, and W72A/W82A) were characterized. Thermal stability and specific activities toward glycol chitin and chitin hexasaccharide were significantly affected by the individual mutations. When N-acetylglucosamine hexamer was hydrolyzed by the wild type, the beta-anomer of the substrate was preferentially hydrolyzed, producing the trimer predominantly and the dimer and tetramer in lesser amounts.