After 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.
