Molecular Characterization of a Mesophilic Cellobiose 2-Epimerase That Maintains a High Catalytic Efficiency at Low Temperatures.

Abstract

Cellobiose 2-epimerase (CE) can catalyze bioconversion of lactose to its prebiotic derivative epilactose. The catalytic property of a novel CE from Treponema brennaborense (Trbr-CE) was investigated. Trbr-CE showed the highest catalytic efficiency of epimerization toward lactose among all of the previously reported CEs. This enzyme's specific activity could reach as high as 208.5 ± 5.3 U/mg at its optimum temperature, which is 45 °C. More importantly, this enzyme demonstrated a considerably high activity at low temperatures, suggesting Trbr-CE as a promising enzyme for industrial low-temperature production of epilactose. This structurally flexible enzyme exhibited a comparatively high binding affinity toward substrates, which was confirmed by both experimental verification and computational analysis. Molecular dynamics (MD) simulations and binding free energy calculations were applied to provide insights into molecular recognition upon temperature changes. Compared with thermophilic CEs, Trbr-CE presents a more negative enthalpy change and a higher entropy change when the temperature drops.