UC Irvine team discovers nitrogenase Fe protein can reduce CO2 to CO; implications for biofuel production
A team at the University of California, Irvine has discovered that the iron protein (the reductase component) of the natural enzyme nitrogenase can, independent of its natural catalytic partner, convert CO2 to carbon monoxide (CO)—a syngas used to produce useful biofuels and other chemical products.
The team, led by Professor Yilin Hu (Molecular Biology and Biochemistry), also found that they could express the reductase component alone in the soil bacterium Azotobacter vinelandii to convert CO2 in a manner more applicable to large-scale production of CO. This whole-cell system could be explored further for new ways of recycling atmospheric CO2 into biofuels and other commercial chemical products. A paper on their work is published in the journal Nature Chemical Biology.
Nitrogenase is a key enzyme in the global nitrogen cycle, and is responsible for the reduction of nitrogen (N2) to ammonia (NH3). The iron (Fe) protein is the reductase component of nitrogenase; a reductase is an enzyme that promotes the chemical reduction of a substance.
In nature, during substrate turnover, the Fe protein forms a functional complex with its catalytic partner, permitting ATP-dependent transfer of electrons from the former to the latter and the subsequent reduction of substrates at the cofactor site of the catalytic component upon accumulation of a sufficient number of electrons.
Such a two-component catalytic system enables two reactions under ambient conditions that are important for energy- and environment-related areas: (i) the reduction of nitrogen (N2) to ammonia (NH3); and (ii) the reduction of carbon monoxide (CO) or carbon dioxide (CO2) to hydrocarbons. Meanwhile, questions have arisen as to whether the actions of Fe proteins can occur in the absence of their respective catalytic partners and what interesting chemistry can be performed by these unique reductases on their own.
To address these questions, we examined the ability of Fe proteins to reduce CO2 in vitro independent of their catalytic partners.—Rebelein et al.
The researchers said that the ability of the Fe protein to effect ambient CO2 reduction opens up new avenues to understand and improve the process of CO2 conversion. Further, the engineered A. vinelandii—a non-carboxydotrophic organism—may offer a possible biotechnological advantage in whole-cell production of syngas CO, as carboxydotrophic organisms predominantly convert CO2 and CO for use in producing their own energy and biomass instead of releasing CO as an unwanted product.
Furthermore, the reaction of CO2 reduction by Fe proteins could be coupled with the reaction of CO reduction by complete nitrogenase systems, which may prove instrumental in developing strategies for sequestration of CO2 concomitant with the conversion of this greenhouse gas into valuable chemical products.—Rebelein et al.
Johannes G Rebelein, Martin T Stiebritz, Chi Chung Lee & Yilin Hu (2016) “Activation and reduction of carbon dioxide by nitrogenase iron proteins” Nature Chemical Biology doi: 10.1038/nchembio.2245