Insights into the structure and function of fungal β-mannosidases from glycoside hydrolase family 2 based on multiple crystal structures of theTrichoderma harzianumenzyme

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Hemicellulose is an important part of the plant cell wall biomass, and is relevant to cellulosic ethanol technologies. β-Mannosidases are enzymes capable of cleaving nonreducing residues of β-d-mannose from β-d-mannosides and hemicellulose mannose-containing polysaccharides, such as mannans and galactomannans. β-Mannosidases are distributed between glycoside hydrolase (GH) families 1, 2, and 5, and only a handful of the enzymes have been structurally characterized to date. The only published X-ray structure of a GH family 2 mannosidase is that of the bacterial Bacteroides thetaiotaomicron enzyme. No structures of eukaryotic mannosidases of this family are currently available. To fill this gap, we set out to solve the structure of Trichoderma harzianum GH family 2 β-mannosidase and to refine it to 1.9-Å resolution. Structural comparisons of the T. harzianum GH2 β-mannosidase highlight similarities in its structural architecture with other members of GH family 2, reveal the molecular mechanism of β-mannoside binding and recognition, and shed light on its putative galactomannan-binding site.DatabaseCoordinates and observed structure factor amplitudes have been deposited with the Protein Data Bank (4CVU and 4UOJ). The T. harzianum β-mannosidase 2A nucleotide sequence has GenBank accession number BankIt1712036 GeneMark.hmm KJ624918.β-Mannosidases are enzymes capable of cleavage of non-reducing residues of β-d-mannose from β-d-mannosides. Here we solved and examined the first structure of eukaryotic glycoside hydrolase family 2 (GH2) β-mannosidase. Structural comparisons of the T. harzianum GH2 β-mannosidase reveal molecular mechanism of the β-d-mannosides binding and recognition and shed light on its putative galactomannan binding site.

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