Screening and characterization of thermostable xylose isomerase from Rhodothermus marinus for erythrose production from one-carbon source.

Four-carbon (C4) sugars, which rarely exist in nature, usually have various biological functions and serve as building units for pharmaceutical agents. For example, erythrose possesses various pharmacological activities. Although several iso/epimerases have a catalytic function on C5/C6 sugars, only a few studies have demonstrated the enzymatic iso/epimerization of C4 sugars. In this work, we presented a xylose isomerase from Rhodothermus marinus possessing isomerization activity toward C4 l-erythrulose. This enzyme showed higher affinity and catalytic efficiency toward l-erythrulose than d-fructose and d-xylulose. Its specific activity reached 24.2 U/mg under optimal reaction conditions, and its half-life was over 8 days at 50 ℃. Demonstration of this enzyme under 833 mM of L-erythrulose gave 130 mM L-erythrose with a conversion yield of 15.6 %. On the basis of this beneficial enzyme, we further designed a multienzyme system and presented a one-pot cascade process for the synthesis of l-erythrose from low-cost, one-carbon formaldehyde (FALD) as the sole feedstock. Given that FALD can be derived from CO2 electrocatalysis or methanol oxidization, l-erythrose synthesis can be realized from methanol and even CO2. l-erythrose can further function as feedstock for synthesizing other high-carbon sugars by coupling enzymatic aldol condensation and reduction reactions.