SusChEM: Novel 1,2-Propanediol Biosynthesis from Renewable Feedstocks through Enzyme Discovery

SusChEM：通过酶发现可再生原料合成新型1,2-丙二醇经过多年的实践，化学工业面临着可持续性挑战，这些挑战来自于化石燃料原料和中间体的潜在减少，以及与生产相关的日益不利的环境成本。生物催化合成，基于酶转化或微生物全细胞合成，越来越多地被探索作为化学生产的替代平台。与化学合成相比，微生物合成的主要优势包括反应选择性、分子多样性、减少对环境的影响，以及利用可再生原料，如植物基纤维素材料，而不是碳氢化合物。微生物合成的成功实施本质上解决了化学工业目前面临的可持续性挑战。由于自然途径往往不适合大规模化学生产，也不能产生理想的化学产品，因此需要努力发现和开发新的工业化学品生物合成途径。内布拉斯加大学林肯分校的牛伟教授和郭建涛教授提出，通过开发一种新的生物合成途径，实现工业散装化学品1,2-丙二醇（1,2- pdo）的可持续生产。1,2 PDO可以整合到其他化学品的生产中，如正丙醇和丙烯。这项研究结合了科学研究的发现和工程方面。参与这项工作的联合国- l学生将获得对基础科学与工程相结合的重要方面和协同效应的看法。多学科研究活动将用于支持积极招募代表性不足的本科生和研究生在STEM领域学习和就业。拟议工作的科学目标是通过减少一种常见的发酵产物乳酸，从可再生原料中建立1,2-丙二醇（一种工业散装化学品和天然产物）的从头生物合成。这两种已知的1,2- pdo生物合成途径的应用受到起始材料稀缺或细胞毒性生物合成中间体参与的限制。pi试图通过使用两种平行方法建立新的1,2- pdo途径来克服这些限制。第一个是一个发现驱动的方法，重点是鉴定在布氏乳杆菌乳酸还原途径中起作用的遗传和催化元件，该途径在缺氧生长条件下产生1,2- pdo。第二种是设计和工程驱动的方法，其重点是开发一种新的人工1,2- pdo生物合成途径，该途径需要将乳酸激活为乳酰辅酶a，然后进行两个连续还原步骤以形成1,2- pdo。该途径还可以实现R-和s -1,2- pdo立体异构体的立体特异性生物合成。牛和郭将应用蛋白质工程技术来提高瓶颈酶——辅酶a依赖性醛脱氢酶的催化效率。为了促进合理的诱变，将努力获得蛋白质的晶体结构，该家族在现有的蛋白质结构数据库中代表性不足。此外，所提出的工作将建立一种新的生长偶联选择方案，以允许快速采样大量的酶突变体。该选择方案有可能适用于具有类似辅因子需求的其他酶的定向进化。

SusChEM: Novel 1,2-Propanediol Biosynthesis from Renewable Feedstocks Through Enzyme DiscoveryAfter many years of practice, the chemical industry faces sustainability challenges that arise from both the potentially dwindling feedstocks and intermediates that are derived from fossil fuels, and from the increasingly undesirable environmental costs associated with their production. Biocatalytic syntheses, based on enzymatic conversion or microbial whole-cell synthesis, are increasingly explored as the alternate platform of chemical production. Key advantages of microbial synthesis over chemical syntheses include reaction selectivity, molecular diversity, and reduced environmental impact, and the utilization of renewable feedstocks, such as plant-based cellulosic material, instead of hydrocarbons. The successful implementation of microbial syntheses inherently addresses the sustainability challenges currently facing the chemical industry. Because natural pathways are often not suitable for large-scale chemical production, and do not lead to desired chemical products, efforts are needed into the discovery and the development of novel biosynthetic pathways for industrial chemicals. Professors Wei Niu and Jiantao Guo at the University of Nebraska-Lincoln propose to achieve sustainable production of an industrial bulk chemical, 1,2-propanediol (1,2-PDO), by developing a new biosynthetic route. 1,2 PDO may be integrated into the production of other chemicals, such as n-propanol and propylene. This study combines both the discovery and the engineering aspects of scientific research. UN-L Students participating in this work will gain perspectives on the important aspects and synergistic effects of integrating basic science and engineering. The multidisciplinary research activities will be used to support active recruitment of underrepresented undergraduate and graduate students to pursue studies and careers in STEM areas.The scientific goal of the proposed work is to establish the de novo biosynthesis of 1,2-propanediol, an industrial bulk chemical and a natural product, from renewable feedstocks through the reduction of a common fermentation product, lactic acid. Application of the two known 1,2-PDO biosynthetic routes is limited either by the scarce availability of the starting material or the involvement of cytotoxic biosynthetic intermediate. The PIs seek to overcome these limitations by establishing novel 1,2-PDO pathways using two parallel approaches. The first one is a discovery-driven approach that focuses on identifying the genetic and catalytic elements that function in the poorly understood lactic acid reduction pathway in Lactobacillus buchneri, which produces 1,2-PDO under anoxic growth conditions. The second one is a design and engineering-driven approach that focuses on the development of a novel artificial 1,2-PDO biosynthetic pathway, which entails the activation of lactic acid as lactoyl-CoA followed by two sequential reduction steps to form 1,2-PDO. This pathway would also enable the stereospecific biosynthesis of R- and S-1,2-PDO stereoisomers. Niu and Guo will apply protein engineering to improve the catalytic efficiency of the bottleneck enzyme, the CoA-dependent aldehyde dehydrogenase. To facilitate rational mutagenesis, efforts will be directed to obtain the crystal structure of the protein, of which the family is underrepresented in available protein structure database. In addition, the proposed work will establish a novel growth-coupled selection scheme to allow rapid sampling of large number of enzyme mutants. The selection scheme has the potential to be adapted for directed evolution of other enzymes that have similar cofactor requirement.