Substrate specificity of glycoside hydrolase family 1 β-glucosidase AtBGlu42 from Arabidopsis thaliana and its molecular mechanism

Plants possess many glycoside hydrolase family 1 (GH1) beta-glucosidases, which physiologically function in cell wall metabolism and activation of bioactive substances, but most remain uncharacterized. One GH1 isoenzyme AtBGlu42 in Arabidopsis thaliana has been identified to hydrolyze scopolin using the gene deficient plants, but no enzymatic properties were obtained. Its sequence similarity to another functionally characterized enzyme Os1BGlu4 in rice suggests that AtBGlu42 also acts on oligosaccharides. Here, we show that the recombinant AtBGlu42 possesses high k(cat)/K-m not only on scopolin, but also on various beta-glucosides, cellooligosaccharides, and laminarioligosaccharides. Of the cellooligosaccharides, cellotriose was the most preferred. The crystal structure, determined at 1.7 angstrom resolution, suggests that Arg342 gives unfavorable binding to cellooligosaccharides at subsite +3. The mutants R342Y and R342A showed the highest preference on cellotetraose or cellopentaose with increased affinities at subsite +3, indicating that the residues at this position have an important role for chain length specificity.

Automated summary

A study found that the enzyme AtBGlu42 in Arabidopsis thaliana can hydrolyze various beta-glucosides, cellooligosaccharides, and laminarioligosaccharides, in addition to hydrolyzing scopolin. Among the cellooligosaccharides, it shows the highest preference for cellotriose. The crystal structure analysis reveals that the Arg342 residue in AtBGlu42 has an unfavorable binding to cellooligosaccharides at subsite +3.