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

<jats:sec><jats:label /><jats:p>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.</jats:p></jats:sec><jats:sec><jats:title>Database</jats:title><jats:p>The atomic coordinates and structure factors (codes <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.rcsb.org/pdb/search/structidSearch.do?structureId=3WH5">3WH5</jats:ext-link>, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.rcsb.org/pdb/search/structidSearch.do?structureId=3WH6">3WH6</jats:ext-link>, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.rcsb.org/pdb/search/structidSearch.do?structureId=3WH8">3WH8</jats:ext-link>, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.rcsb.org/pdb/search/structidSearch.do?structureId=3WH7">3WH7</jats:ext-link>, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.rcsb.org/pdb/search/structidSearch.do?structureId=5AYB">5AYB</jats:ext-link>, and <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.rcsb.org/pdb/search/structidSearch.do?structureId=5AYI">5AYI</jats:ext-link>) have been deposited in the Protein Data Bank (<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://wwpdb.org/">http://wwpdb.org/</jats:ext-link>).</jats:p></jats:sec>