Making starch faster than field crops do, without using living cells

Researchers have developed a novel, cell-free method of synthesizing starch, the common plant carbohydrate, from carbon dioxide (CO₂) and hydrogen using a combination of chemical catalysts and a carefully selected set of enzymes in a cell-free approach. This work could provide a pathway toward future industrial biomanufacturing of the important substance. Starch is the most consumed caloric component of human nutrition and animal feed, and an important industrial feedstock used for products ranging from paper to bioplastics. Commonly used for long-term energy storage in roots and seeds, natural starch synthesis in plants is a complex process, which converts glucose from photosynthesis into amylose and amylopectin polymers that make up insoluble starch granules. Currently, the vast majority of global starch supply is derived from agricultural crops. However, efforts to improve starch synthesis in plants are limited by the complexity and inefficiency of the biological processes involved. And, while widely regarded as an attractive alternative, artificial starch synthesis remains challenging. Here, Tao Cai and colleagues present the artificial starch anabolic pathway (ASAP) – a chemical-biochemical hybrid process for starch synthesis from CO₂ and hydrogen without the use of living cells. The chemoenzymatic system uses an inorganic catalyst to reduce CO₂ to methanol, which is then converted by bioengineered enzymes into sugars, and then into polymeric starch. According to Cai et al., ASAP can convert CO₂ to starch at a rate of 22 nanomoles of CO₂ per minute per milligram of total catalysis, which equates to roughly an 8.5-fold higher rate than starch synthesis in field crops.