Cell-free chemoenzymatic starch synthesis from carbon dioxide

• Published in: Science (American Association for the Advancement of Science) Vol. 373; no. 6562; pp. 1523 - 1527
• Main Authors: Cai, Tao, Sun, Hongbing, Qiao, Jing, Zhu, Leilei, Zhang, Fan, Zhang, Jie, Tang, Zijing, Wei, Xinlei, Yang, Jiangang, Yuan, Qianqian, Wang, Wangyin, Yang, Xue, Chu, Huanyu, Wang, Qian, You, Chun, Ma, Hongwu, Sun, Yuanxia, Li, Yin, Li, Can, Jiang, Huifeng, Wang, Qinhong, Ma, Yanhe
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 24.09.2021
• Subjects: Amylopectin; Amylose; Calories; Carbohydrates; Carbon dioxide; Carbon fixation; Catalysts; Cell-free system; Chemical synthesis; Computer applications; Energy storage; Enzymes; Hybrid systems; Modular design; Modular engineering; Photosynthesis; Polymers; Protein engineering; Seeds; Starch; Starches; Synthesis
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.abh4049

Many plants turn glucose from photosynthesis into polymers that form insoluble starch granules ideal for long-term energy storage in roots and seeds. Cai et al . developed a hybrid system in which carbon dioxide is reduced to methanol by an inorganic catalyst and then converted by enzymes first to three and six carbon sugar units and then to polymeric starch. This artificial starch anabolic pathway relies on engineered recombinant enzymes from many different source organisms and can be tuned to produce amylose or amylopectin at excellent rates and efficiencies relative to other synthetic carbon fixation systems—and, depending on the metric used, even to field crops. —MAF A designed chemoenzymatic cascade reaction enables cell-free synthesis of starch from carbon dioxide. Starches, a storage form of carbohydrates, are a major source of calories in the human diet and a primary feedstock for bioindustry. We report a chemical-biochemical hybrid pathway for starch synthesis from carbon dioxide (CO 2 ) and hydrogen in a cell-free system. The artificial starch anabolic pathway (ASAP), consisting of 11 core reactions, was drafted by computational pathway design, established through modular assembly and substitution, and optimized by protein engineering of three bottleneck-associated enzymes. In a chemoenzymatic system with spatial and temporal segregation, ASAP, driven by hydrogen, converts CO 2 to starch at a rate of 22 nanomoles of CO 2 per minute per milligram of total catalyst, an ~8.5-fold higher rate than starch synthesis in maize. This approach opens the way toward future chemo-biohybrid starch synthesis from CO 2 .