Xu Qiang-Sheng, Yan Yu-Si, Feng Jia-Xun
State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, Guangxi Key Laboratory of Subtropical Bioresources Conservation and Utilization, Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, 530004 Guangxi People's Republic of China.
Biotechnol Biofuels. 2016 Oct 18;9:216. doi: 10.1186/s13068-016-0636-5. eCollection 2016.
Starch is a very abundant and renewable carbohydrate and is an important feedstock for industrial applications. The conventional starch liquefaction and saccharification processes are energy-intensive, complicated, and not environmentally friendly. Raw starch-digesting glucoamylases are capable of directly hydrolyzing raw starch to glucose at low temperatures, which significantly simplifies processing and reduces the cost of producing starch-based products.
A novel raw starch-digesting glucoamylase PoGA15A with high enzymatic activity was purified from GXU20 and biochemically characterized. The PoGA15A enzyme had a molecular weight of 75.4 kDa, and was most active at pH 4.5 and 65 °C. The enzyme showed remarkably broad pH stability (pH 2.0-10.5) and substrate specificity, and was able to degrade various types of raw starches at 40 °C. Its adsorption ability for different raw starches was consistent with its degrading capacities for the corresponding substrate. The cDNA encoding the enzyme was cloned and heterologously expressed in . The recombinant enzyme could quickly and efficiently hydrolyze different concentrations of raw corn and cassava flours (50, 100, and 150 g/L) with the addition of α-amylase at 40 °C. Furthermore, when used in the simultaneous saccharification and fermentation of 150 g/L raw flours to ethanol with the addition of α-amylase, the ethanol yield reached 61.0 g/L with a high fermentation efficiency of 95.1 % after 48 h when raw corn flour was used as the substrate. An ethanol yield of 57.0 g/L and 93.5 % of fermentation efficiency were achieved with raw cassava flour after 36 h. In addition, the starch-binding domain deletion analysis revealed that SBD plays a very important role in raw starch hydrolysis by the enzyme PoGA15A.
A novel raw starch-digesting glucoamylase from , with high enzymatic activity, was biochemically, molecularly, and genetically identified. Its efficient hydrolysis of raw starches and its high efficiency during the direct conversion of raw corn and cassava flours via simultaneous saccharification and fermentation to ethanol suggests that the enzyme has a number of potential applications in industrial starch processing and starch-based ethanol production.
淀粉是一种极为丰富且可再生的碳水化合物，是工业应用的重要原料。传统的淀粉液化和糖化过程能源消耗大、工艺复杂且不环保。生淀粉消化型糖化酶能够在低温下直接将生淀粉水解为葡萄糖，这显著简化了加工过程并降低了淀粉基产品的生产成本。
从GXU20中纯化出一种具有高酶活性的新型生淀粉消化型糖化酶PoGA15A，并对其进行了生化特性分析。PoGA15A酶的分子量为75.4 kDa，在pH 4.5和65℃时活性最高。该酶表现出显著宽泛的pH稳定性（pH 2.0 - 10.5）和底物特异性，并且能够在40℃下降解各种类型的生淀粉。其对不同生淀粉的吸附能力与其对相应底物的降解能力一致。编码该酶的cDNA被克隆并在……中进行了异源表达。重组酶在40℃下添加α -淀粉酶时能够快速有效地水解不同浓度的生玉米粉和木薯粉（50、100和150 g/L）。此外，当用于将150 g/L生面粉同时糖化发酵为乙醇并添加α -淀粉酶时，以生玉米粉为底物时，48小时后乙醇产量达到61.0 g/L，发酵效率高达95.1%。以生木薯粉为底物时，36小时后乙醇产量为57.0 g/L，发酵效率为93.5%。此外，淀粉结合结构域缺失分析表明，SBD在PoGA15A酶水解生淀粉过程中起着非常重要的作用。
从……中鉴定出一种具有高酶活性的新型生淀粉消化型糖化酶，并对其进行了生化、分子和遗传鉴定。它对生淀粉的高效水解以及在将生玉米粉和木薯粉直接通过同时糖化发酵转化为乙醇过程中的高效率表明，该酶在工业淀粉加工和淀粉基乙醇生产中具有许多潜在应用。
