酶法催化甲醛合成木酮糖

Enzymatic synthesis of xylulose from formaldehyde

摘要:

木酮糖是生物体内的代谢中间产物，是多种稀有糖合成的前体物质，因其独特的生物活性在膳食、保健、医药等领域发挥着重要作用。本研究旨在从最基本有机原料之一的甲醛出发，利用生物酶法催化甲醛合成木酮糖。通过来源于恶臭假单胞菌Pseudomonas putida的苯甲酸脱羧酶 (Benzoylformate decarboxylase) 突变体BFD-M3催化甲醛聚合生成羟基乙醛和1,3-二羟基丙酮 (DHA)。通过来源于大肠杆菌的转醛醇酶 (Transaldolase)突变体TalB-F178Y进一步催化羟基乙醛和DHA聚合生成木酮糖，最终实现甲醛到木酮糖的酶法转化，转化率为0.4%。此外，经过优化甲醛底物浓度，木酮糖转化率达到4.6%，比优化前提高了11.5倍。为了进一步提高木酮糖的转化率，采用Scaffold多酶组装技术固定BFD-M3、TalB-F178Y蛋白，使木酮糖转化率达到14.02%，较未用Scaffold技术前提高3倍，为生物法合成稀有糖提供了一种新方案。

Abstract:

Xylulose as a metabolic intermediate is the precursor of rare sugars, and its unique pattern of biological activity plays an important role in the fields of food, health, medicine and so on. The aim of this study was to design a new pathway for xylulose synthesis from formaldehyde, which is one of the most simple and basic organic substrate. The pathway was comprised of 3 steps: (1) formaldehyde was converted to glycolaldehyde by benzoylformate decarboxylase mutant BFD-M3 (from Pseudomonas putida); (2) formaldehyde and glycolaldehyde were converted to dihydroxyacetone by BFD-M3 as well; (3) glycolaldehyde and dihydroxyacetone were converted to xylulose by transaldolase mutant TalB-F178Y (from Escherichia coli). By adding formaldehyde (5 g/L), BFD-M3 and TalB-F178Y in one pot, xylulose was produced at a conversion rate of 0.4%. Through optimizing the concentration of formaldehyde, the conversion rate of xylulose was increased to 4.6% (20 g/L formaldehyde), which is 11.5 folds higher than the initial value. In order to further improve the xylulose conversion rate, we employed Scaffold Self-Assembly technique to co-immobilize BFD-M3 and TalB-F178Y. Finally, the xylulose conversion rate reached 14.02%. This study provides a new scheme for the biosynthesis of rare sugars.