Crystal structure and identification of a key amino acid for glucose tolerance, substrate specificity, and transglycosylation activity of metagenomic β-glucosidase Td2F2


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Abstract

β-Glucosidase Td2F2 isolated from a compost metagenome has high glucose tolerance and transglycosylation activity. In this study, we determined the high-resolution crystal structure of Td2F2. It has a unique structure at the −1 subsite that is important for substrate specificity but not for glucose tolerance. To elucidate the mechanism(s) of glucose tolerance, we isolated a glucose-sensitive Td2F2 mutant using random mutagenesis. In this mutant, Asn223 residue located between subsites +1 and +2 was mutated. The Asn223 mutation resulted in reduced glucose tolerance and transglycosylation activity, and drastically changed substrate specificity. These results indicate that the structure between subsites +1 and +2 is critical for the glucose tolerance and substrate specificity of Td2F2. Our findings shed light on the glucose tolerance and transglycosylation activity mechanisms of glycoside hydrolase family 1 β-glucosidases.DatabaseThe atomic coordinates and structure factors (codes 3WH5, 3WH6, 3WH8, 3WH7, 5AYB, and 5AYI) have been deposited in the Protein Data Bank (http://wwpdb.org/).The high-resolution crystal structure of β-glucosidase Td2F2, which has high glucose tolerance and transglycosylation activity, was determined. Asn223 residue located between subsites +1 and +2 was responsible for glucose tolerance, transglycosylation, and substrate specificity. Our findings shed light on the glucose tolerance and transglycosylation activity mechanisms of glycoside hydrolase family 1 β-glucosidases.

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