Abstract:
Plant cell walls are composed of a heterogeneous mixture of polysaccharides that require several different enzymes to
degrade. These enzymes are important for a variety of biotechnological processes, from biofuel production to food processing. Several classical mannanolytic enzyme functions of glycoside hydrolases (GH), such as β-mannanase, β-mannosidase
and α-galactosidase activities, are helpful for efficient mannan hydrolysis. In this light, we bring three enzymes into the
model of mannan degradation that have received little or no attention. By linking their three-dimensional structures and
substrate specificities, we have predicted the interactions and cooperativity of these novel enzymes with classical mannanolytic enzymes for efficient mannan hydrolysis. The novel exo-β-1,4-mannobiohydrolases are indispensable for the
production of mannobiose from the terminal ends of mannans, this product being the preferred product for short-chain
mannooligosaccharides (MOS)-specific β-mannosidases. Second, the side-chain cleaving enzymes, acetyl mannan esterases (AcME), remove acetyl decorations on mannan that would have hindered backbone cleaving enzymes, while the
backbone cleaving enzymes liberate MOS, which are preferred substrates of the debranching and sidechain cleaving
enzymes. The nonhydrolytic expansins and swollenins disrupt the crystalline regions of the biomass, improving their
accessibility for AcME and GH activities. Finally, lytic polysaccharide monooxygenases have also been implicated in promoting the degradation of lignocellulosic biomass or mannan degradation by classical mannanolytic enzymes, possibly by
disrupting adsorbed mannan residues. Modelling effective enzymatic mannan degradation has implications for improving
the saccharification of biomass for the synthesis of value-added and upcycling of lignocellulosic wastes.
