A Novel AGE Family Epimerase/Isomerase and Its Application in d-Mannose Synthesis.

d-mannose has exhibited excellent physiological properties in the food, pharmaceutical, and feed industries. Therefore, emerging attention has been applied to enzymatic production of d-mannose due to its advantage over chemical synthesis. The gene of -acetyl-d-glucosamine 2-epimerase family epimerase/isomerase (AGEase) derived from was amplified, and the recombinant AGEase was characterized. The optimal temperature and pH of AGEase were 60 °C and 7.5, respectively. The , , and / of AGEase for d-mannose were 49.2 ± 8.5 mM, 476.3 ± 4.0 s, and 9.7 ± 0.5 s·mM, respectively. The recombinant AGEase was classified into the YihS enzyme subfamily in the AGE enzyme family by analyzing its substrate specificity and active center of the three-dimensional (3D) structure. Further studies on the kinetics of different substrates showed that the AGEase belongs to the d-mannose isomerase of the YihS enzyme. The AGEase catalyzed the synthesis of d-mannose with d-fructose as a substrate, and the conversion rate was as high as 39.3% with the d-mannose yield of 78.6 g·L under optimal reaction conditions of 200 g·Ld-fructose and 2.5 U·mL AGEase. This novel AGEase has potential applications in the industrial production of d-mannose.