l-Erythrulose Synthesis From Glycerol by a Multienzymatic Cascade Reaction

Upgrading glycerol (GLY), an abundant bio-based platform chemical, into high-value oxygenates is a cornerstone of integrated biorefineries. While chemo-catalytic routes typically suffer of a lack of selectivity, enzymatic approaches are often limited in productivity and robustness. Glycerol dehydrogenase (GDH) catalyzes the selective oxidation of glycerol into the valuable compound dihydroxyacetone (DHA). However, this biocatalytic reaction is hampered by strong product inhibition of the enzyme and by the requirement for the costly cofactor NAD⁺. The enzyme is also inhibited by the formed NADH. To overcome these limitations, we designed a biocatalytic cascade system. In this approach, fructose-6-phosphate aldolase (FSA_A129S) rapidly converts DHA, thereby preventing inhibition and funneling the reaction toward the formation of l-erythrulose, a stable, noninhibitory, and more valuable product. In addition, an optimized cofactor regeneration system based on NADH oxidase and catalase (NOX) is incorporated so that only a catalytic amount of NAD⁺ is required. All four enzymes are co-immobilized on a resin to create a multifunctional heterogeneous biocatalyst. Using this system, l-erythrulose is produced at concentrations up to 120 mM with complete selectivity.