In 2021, Ma Yanhe, a researcher at the Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, led a team to design and construct an unnatural carbon sequestration and starch synthesis pathway of the 11-step reaction from scratch in a "building block" similar method, realizing the total synthesis from carbon dioxide to starch molecules for the first time in the laboratory. Nuclear magnetic resonance and other tests found that the structural composition of synthetic starch molecules and natural starch molecules was consistent. Preliminary laboratory tests have shown that synthetic starch is about 8.5 times more efficient than starch produced in traditional agriculture. Under the condition of sufficient energy supply, according to the current technical parameters, the annual starch output of a bioreactor of 1 cubic meter in size is theoretically equivalent to the annual starch output of 5 mu of corn land in the mainland. (Related report: Science heavy: mainland scientists break through CO₂ synthetic starch technology!) ）
Netizens joked: In the future, there is no need to farm, drinking the northwest wind can be full!
In the latest issue of the journal Nature, in another big discovery, scientists have found an enzyme that can convert air into electricity. Netizens will not only drink the northwest wind in the future, but also generate electricity. Professor Chris Greening's team at Monash University's Institute of Biomedical Discovery in Melbourne, Australia, isolated a Huc enzyme from bacteria that harnesses small amounts of hydrogen in the atmosphere to produce an electric current. If this enzyme could one day be bioengineered to be produced on a large scale, the sky is the limit for using it to produce clean energy.
An enzyme that harvests electrical energy from the air
Obtaining electricity directly from the air may seem like science fiction, but in fact, there are organisms in nature that have long been able to do it. According to previous studies, there are a variety of aerobic bacteria in the world that use H2 in the atmosphere as an energy source for growth and survival. At this stage, at least 9 phyla of various aerobic bacteria can achieve H2 oxidation in the atmosphere, and these bacteria remove 75% (about 60Tg) of the total H2 from the atmosphere every year. H2 oxidation in the atmosphere provides bacteria with complementary energy in nutrient-limited soil environments, allowing them to grow or remain dormant but active for long periods of time by air alone. For example, mycobacterial cells and Streptomyces spores survive starvation by transferring electrons from atmospheric H2 to O2 through an aerobic respiratory chain. Therefore, the ability to oxidize H2 in the atmosphere is widely present in bacteria in different environments.
In order to be able to realize the utilization of H2 in the atmosphere using these enzymes, the catalytic processes of these enzymes need to be carefully studied. Existing studies have shown that H2 oxidation in the atmosphere is done by members of the [NiFe] hydrogenase family. But this enzyme is easily reversibly or irreversibly inhibited by O2. As a result, how these enzymes overcome the extraordinary catalytic challenge of oxidizing picomolar levels of H2 at environmental levels of the catalytic poison O2, and how to transfer derived electrons to the respiratory chain, remains poorly studied.
Recently, to fill these knowledge gaps, Chris Greening's team at Monash University studied aerobic bacteria M. Structural and mechanistic basis of atmospheric H2 oxidation of smegmatis. By directly from M. Huc was isolated from smegmatis, the structure and biochemical basis of its oxidation of H2 in the atmosphere was determined, and the cryo-electron microscopy structure of the hydrogenase Huc of Penicillium nicholica was determined, revealing its mechanism and determining the structural and biochemical basis of its oxidation of H2 in the atmosphere. These findings provide a mechanistic basis for biogeochemically and ecologically important atmospheric H2 oxidation processes, discover an energy-coupled mode that relies on long-distance quinone transport, and pave the way for the development of catalysts for ambient air H2 oxidation. The work was published in Nature as an article titled "Structural basis for bacterial energy extraction from atmospheric hydrogen."
The researchers used Strep-tag II on the HucS subunit encoded by chromosomes, from M. Huc was isolated from smegmatis. The extracted Huc enzyme converts hydrogen into an electric current. Huc is highly efficient, has an inherent ability to oxidize H2 at subatmospheric concentrations, and is largely insensitive to O2 inhibition. Unlike all other known enzymes and chemical catalysts, it consumes even hydrogen below atmospheric levels, making up only 0.00005% of the air. In addition, Huc is very stable. The enzyme can be frozen or heated to 80 degrees Celsius, and it retains its ability to produce energy, thus reflecting the enzyme helping bacteria survive in the most extreme environments.
The SDS-PAGE analysis showed that Huc consists of three protein subunits, corresponding to HucL (about 58 kDa), HucS-2× Strep (about 39 kDa), and a third unknown subunit (about 18 kDa). The third subunit is the unqualified protein MSMEG_2261, which is encoded by an open reading frame in the huc operon directly upstream of hucS17. The ability of purified Huc to oxidize H2 from 3 to 100 ppm in ambient air was tested. Using nitroblue tetrazole (NBT) or quinone analogue menaquinone as the electron acceptor, Huc rapidly depletes H2, bringing it below the detection limit of the gas chromatograph (approximately 40 ppbv). Kinetic analysis of purified Huc showed that it adapted to oxidize atmospheric H2, with high affinity (Km = 129 nM) and low H2 threshold (<31 pM), but slow turnover (catalytic constant (kcat) = 7.05 s-1), indicating that the enzyme is very efficient at low H2 concentrations.
Cryo-electron microscope images show that Huc has a molecular shape like a four-leaf clover, which is associated with membrane vesicles through a stalk-like protrusion. The four lobes of the Huc are each composed of two Huc protosomes, each consisting of HucS and HucL subunits. Four Huc lobes are combined with a scaffold formed by four HucM molecules, an elongated, α spiral-shaped protein that intertwine to form a cage-like structure.
Studies have shown that Huc's tolerance to oxygen is due to its narrow channels of hydrophobic gas. To determine whether these channels play a role in the stereoscopic exclusion of O2 from the active site of Huc, all-atomic molecular dynamics simulations were performed on HucSL dimers in the presence of excess H2 and water-soluble O2. In these simulations, H2 enters the Huc active site, while O2 is three-dimensionally excluded by a series of bottlenecks between the active site and the enzyme surface, and does not approach the catalytic cluster. The simulation results show that the key point for selecting O2 is the bottleneck after the convergence of the three gas channels immediately adjacent to the inlet of the active site. This indicates that the Huc gas channel plays a role in protecting the [NiFe] cluster from being inactivated by O2.
Summary: To take advantage of the trace amounts of H2 present in the air, the authors used aerobic bacteria M. The biochemical and electrochemical properties of smegmatis' Huc enzyme suggest that properties that are insensitive to O2 and high affinity for H2 are inherent in this hydrogenase and not due to coupling to other processes within bacterial cells. In addition, by determining the low-temperature EM structure and molecular dynamics simulation of Huc, strong evidence was provided that the exclusion of O2 from at least partially the active site contributed to the O2 insensitivity of the enzyme. These findings open the way for the development of biocatalysts, as all hydrogenases applied to date in whole-cell and purified enzyme systems are low-affinity enzymes that are inhibited by O2. As an oxygen-insensitive, high-affinity enzyme and [NiFe]hydrogenase, Huc provides the basis for the development of biocatalysts that operate under environmental conditions.