Microbial ß-mannosidases and their industrial applications.

Heteropolymers of mannan are polysaccharide components of the plant cell wall of gymnosperms and some angiosperms, including palm trees (Arecales and Monocot). Degradation of the complex structure of these polysaccharides requires the synergistic action of enzymes that disrupt the internal carbon skeleton of mannan and accessory enzymes that remove side chain substituents. However, complete degradation of these polysaccharides is carried out by an exo-hydrolase termed ß-mannosidase. Microbial ß-mannosidases belong to families 1, 2, and 5 of glycosyl hydrolases, and catalyze the hydrolysis of non-reducing ends of mannose oligomers. Besides, these enzymes are also involved in transglycosylation reactions. Because of their activity at different temperatures and pH values, these enzymes are used in a variety of industrial applications and the pharmaceutical, food, and biofuel industries.

Insights into the structure and function of fungal ß-mannosidases from glycoside hydrolase family 2 based on multiple crystal structures of the Trichoderma harzianum enzyme.

UNLABELLED: Hemicellulose is an important part of the plant cell wall biomass, and is relevant to cellulosic ethanol technologies. ß-Mannosidases are enzymes capable of cleaving nonreducing residues of ß-d-mannose from ß-d-mannosides and hemicellulose mannose-containing polysaccharides, such as mannans and galactomannans. ß-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 ß-mannosidase and to refine it to 1.9-Å resolution. Structural comparisons of the T. harzianum GH2 ß-mannosidase highlight similarities in its structural architecture with other members of GH family 2, reveal the molecular mechanism of ß-mannoside binding and recognition, and shed light on its putative galactomannan-binding site. DATABASE: Coordinates and observed structure factor amplitudes have been deposited with the Protein Data Bank (4CVU and 4UOJ). The T. harzianum ß-mannosidase 2A nucleotide sequence has GenBank accession number BankIt1712036 GeneMark.hmm KJ624918.