How alginate lyase produces quasi-monodisperse oligosaccharides: a normal mode analysis-based docking and molecular dynamics simulation study

Polysaccharide degradation products are widely used in medicine, health food, textile and other industries. The preparation of monosaccharides by enzymatic degradation is a key technology in bio industrial production. Unfortunately, most of the known digested products are complex oligosaccharide mixtures, which limit their industrial processing and application. In this study, we explored a docking technique based on normal mode analysis to examine the possible cleavage mechanism of an alginate lyase (AlyB) from Birio Splendidus , which contains the catalytic domain of polysaccharide lyase family 7 (PL7) and a CBM32 sugar binding module, and was observed to produce trisaccharide products with quasi-monosaccharide distribution. We compared the molecular interactions of the enzyme with the natural alginates, the polyMG whose products has the quasi-monodisperse distribution of tri-saccharide and two synthetic polysaccharides, the polyM and polyG whose products has a wider distribution of oligosaccharides. Our calculations quantitatively show that there are a series of deterministic conformational changes in the catalytic pocket, which control the specificity of the substrate; at the same time, it determines the uniformity of the final product together with the spatial position of the key catalytic sites. The dynamic simulations revealed that CBM domain plays a key role in assisting the release of tri-saccharides. Our data highlights the important role of enzyme flexibility in determining product uniformity, which may provide new insight into design of enzymes for the production of high-value mono-distributed oligosaccharides.