Curdlan conformation change during its hydrolysis by multi-domain β-1,3-glucanases

Enzymatic curdlan hydrolysis is gaining more attention for the value of oligo-β-glucans in many aspects. Currently, the triple-helical conformation of curdlan fiber was imposed to the structure of β-1,3-glucanase as its substrate without experimental evidence. Here, solution conformation of differently treated curdlan and each hydrolysis rate by a variety of β-1,3-glucanases were systematically examined. Results showed that different enzymes exhibited preferences over the trajectories of pH change that curdlan solution went through, and all enzymes hydrolyzed heat treated curdlan solution at their maximum rates where most of the higher ordered helices were diminished. Combined with molecular docking studies, a multi-step hydrolysis process was proposed. Recognition of triple-helical curdlan by their ancillary region of β-1,3-glucanase occurred before its unwinding into single- and double-helical forms, and the later ones fitted better to the catalytic cavity of the enzyme where the polysaccharides chain eventually got hydrolyzed into oligo-β-glucans.