If you want a sustainable, renewable way to convert sunlight into other forms of energy, look to green plants and algae. Photosynthesis by these organisms turns sunlight into cellular energy with exceptional efficiency. A key player in this conversion is a large protein complex called NAD(P)H dehydrogenase-like complex (NDH). Researchers built a detailed blueprint of NDH, showing where the vast majority of the atoms reside and how NDH connects to others. With this structure, researchers can generate and test hypotheses about how NDH works, specifically how it acquires and transfers electrons.
The team’s structural model will let scientists explore the inner workings of this key component of photosynthesis. Relatives of this model are found in many organisms including humans. Ultimately, knowledge of NDH could lead to better ways to produce fuels, biodegradable plastics, and other products using photosynthetic organisms.
Discovered decades ago, a large protein complex called NAD(P)H dehydrogenase-like complex (NDH) helps regulate the steps of photosynthesis where solar energy is captured and stored in two types of cellular energy molecules, ATP and NADPH. These molecules are later used to power the conversion of carbon dioxide to sugar. NDH plays multiple roles in photosynthesis, but the most important is to balance the ratio of ATP and NADPH made by photosynthesis for maximum efficiency of carbon dioxide uptake. NDH is large and complicated. To truly know how it works, the team needed its molecular blueprint. They isolated NDH complexes from membranes of a photosynthetic cyanobacterium (a.k.a. blue-green algae) and imaged them using a cryo-transmission electron microscope fitted with a new electron-counting camera. The researchers took digital movies of the protein complex at an extremely high frame rate. This rate lets scientists align individual frames to eliminate blurring. Using the images, the team built a model of NDH that shows the arrangement of all the protein subunits and the most likely position of all the atoms. By examining the model, the team will formulate and then test hypotheses about how NDH works, specifically how it receives electrons from other proteins and the multiple paths followed by the electrons as they pass through it — details that are critical to understanding how sunlight is used to make energy-carrying molecules such as sugars and other energy-rich molecules.
This research was funded by the following: National Science Foundation Graduate Research Fellowship (T.G.L.); Molecular Basis of Cell Function National Institutes of Health pre-doctoral training program (T.G.L.); Healthy Brain for Health Lives studentship (A.N.B.); Tier 2 Canada Research Chair (J.F.T.); Department of Energy, Office of Science, Basic Energy Sciences (D.F.S. and K.M.D.).
T.G. Laughlin, A.N. Bayne, J.F. Trempe, D.F. Savage, and K.M. Davies, “Structure of the complex I-like molecule NDH of oxygenic photosynthesis.” Nature 566, 411 (2019). [DOI: 10.1038/s41586-019-0921-0]