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The enzymatic hydrolysis of barley beta-glucan, konjac glucomannan and carboxymethyl cellulose by a β-1,4-D-endoglucanase MeCel45A from blue mussel, Mytilus edulis, which belongs to subfamily B of glycoside hydrolase family 45 (GH45), was compared with GH45 members of subfamilies A (Humicola insolens HiCel45A), B (Trichoderma reesei TrCel45A) and C (Phanerochaete chrysosporium PcCel45A). Furthermore, the crystal structure of MeCel45A is reported. Initial rates and hydrolysis yields were determined by reducing sugar assays and product formation was characterized using NMR spectroscopy. The subfamily B and C enzymes exhibited mannanase activity, whereas the subfamily A member was uniquely able to produce monomeric glucose. All enzymes were confirmed to be inverting glycoside hydrolases. MeCel45A appears to be cold adapted by evolution, as it maintained 70% activity on cellohexaose at 4 °C relative to 30 °C, compared to 35% for TrCel45A. Both enzymes produced cellobiose and cellotetraose from cellohexaose, but TrCel45A additionally produced cellotriose., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Here we describe the first crystal structure of a beta‐1,4‐endoglucanase from a brown‐rot fungus, Gloeophyllum trabeum GtCel45A, which belongs to subfamily C of glycoside hydrolase family 45 (GH45). GtCel45A is ~ 18 kDa in size and the crystal structure contains 179 amino acids. The structure is refined at 1.30 Å resolution and Rfree 0.18. The enzyme consists of a single catalytic module folded into a six‐stranded double‐psi beta‐barrel domain surrounded by long loops. GtCel45A is very similar in sequence (82% identity) and structure to PcCel45A from the white‐rot fungus Phanerochaete chrysosporium. Surprisingly though, initial hydrolysis of barley beta‐glucan was almost twice as fast in GtCel45A as compared to PcCel45A. [ABSTRACT FROM AUTHOR]