How hydrogenases work at the atomic level

点击翻译按钮获取中文摘要

Renewable energy is synonymous with exploiting sunlight, but the sun does not always shine. In green plants, energy from sunlight is stored by using it to convert water and carbon dioxide into sugars and oxygen. Scientists are very interested in discovering ways of mimicking the processes occurring in the green leaf, not so much to produce sugars but to make hydrogen (H2) by splitting water an abundant resource. Hydrogen, the smallest of all molecules, is therefore the most important primary fuel of the future: aside from using sunlight itself, H2 can be produced from any common source of electrical energy (such as surplus electricity from windfarms). The energy stored in H2 is released either by combustion or by its conversion back into electricity in fuel cells, but H2 is also a raw material for making fertilisers and other chemicals including liquid fuels for transport. In learning how to use and produce H2 most efficiently, at low cost, scientists are looking again to nature itself. Much progress has recently been made in discovering how effective microorganisms are in producing and using hydrogen as a metabolite, and many details of the mechanism by which enzymes known as hydrogenases catalyse this reaction are now known. 'Activating' hydrogen means making or breaking the chemical bond between two hydrogen atoms. Electrons are moved into or from the hydrogen molecule from other atoms in the active site of hydrogenases, and just tiny distances are critical. The enzymes have evolved to have every atom of the active site in just the right place. The research to be carried out will identify the positions and roles of each of the different atoms of the active site of hydrogenases, leading scientists to a 'blueprint' by which to create the hydrogen catalysts of the future. To determine this information at the atomic level requires genetic engineering to be combined with structural definition at the highest resolution possible using x-ray diffraction. It is not easy to detect the positions of hydrogen atoms by x-rays and this is particularly the case when they are in giant molecules like enzymes: therefore an important challenge will be to achieve extremely high resolution by careful attention to sample homogeneity and crystallisation. Efforts will also be made to test the feasibility of obtaining a structure of a hydrogenase 'trapped in action' by making a genetically-engineered variant in which H2 is bound but cannot react further. The ultimate goal of the research would be to see if the structure of such a 'trapped in action' hydrogenase can be determined using neutron diffraction, as neutrons are able to pinpoint the accurate position of hydrogen atoms, making it possible to observe the hydrogen molecule itself.