Carbohydrate-Binding Modules in Plant Cell Wall-Degrading Enzymes

Structural polysaccharides in plant cell walls are one of the most abundant organic matters and renewable energy sources. Bioconversion of these polysaccharides to fuels and chemicals has attracted tremendous interest to address problems related with climate change and energy security. In nature, these polysaccharides are efficiently degraded with microorganisms having a set of hydrolytic enzymes. These degradations by microbes play an important role on carbon flow in biosphere. The elucidation of the mechanisms how these microorganisms deconstruct these polysaccharides is crucial for efficient bioconversions. In general, these polysaccharides are insoluble and recalcitrant against enzymatic hydrolysis. To date, enormous works have tried to understand the degradation mechanisms. Carbohydrate-binding modules (CBMs) in polysaccharide degrading enzymes are defined as protein domains recognizing sugars. Especially, polysaccharides in plant cell walls are insoluble, therefore the enzymes have to bind to the surface of the substrates. And these enzymes have to react at interface between water and insoluble polysaccharides. CBMs play a role on enzymes directed their substrates. Recently, there are more comprehensive review articles described on CBMs (1-4). In this review, CBMs, especially in plant cell walls degrading enzymes are focused.