Oxygenic photosynthesis is one of the most important biological processes that has ever arisen and paved the way for all complex life on Earth. Our team aims to understand multiple facets of oxygenic photosynthesis, mostly based around the structure-function relationship in the photo-active oxidoreductases, Photosystem I (PSI) and Photosystem II (PSII), and their affiliated antenna systems. To perform these investigations, we employ a variety of structure-based methods such as traditional X-ray crystallography, serial femtosecond crystallography (SFX), and cryo-electron microscopy. This, in turn, gives us insight into such topics as the mechanism of water-oxidation, how electrons are transferred through the reaction center cofactors, how energy is transferred throughout the antenna systems, how these protein complexes are assembled in vivo, and more. In addition to important fundamental understanding of natural processes, this research has vast implications in genetic engineering and photovoltaic design.

The following table provides descriptions of energy-related projects being performed in the Fromme lab.

Serial femtosecond crystallography (SFX) has revolutionized the field of structural biology. In these experiments, many small crystals are used to collect X-ray diffraction at an X-ray Free Electron Laser source (XFEL). Following a light-excitation sequence, a single diffraction pattern is collected from each crystal before the crystal is destroyed by the beam. This allows for a completely radiation damage-free data set which can be analyzed to solve structures. Because of the ability to vary excitation time delays, we can solve these structures in various excited states, essentially making a molecular movie of the enzyme that constitutes the crystal while it performs its function. The new Biodesign C building is the base for building the first “compact” XFEL which will drastically increase the accessibility to XFEL technology to researchers around the world. We use this technology to study electron transfer and water oxidation in PSI and PSII.

Project Leader: Chris Gisriel

Algae biomass is made up mostly of lipids, proteins and carbohydrates all made from CO2, which can be used as sustainable fuels, food and fiber (materials) to help society. We are working on ways to improve how the algae utilize CO2 and accelerate their growth to make economical fuels and products.

Project Leader: Justin Flory

Adenosine triphosphate (ATP) is the universal chemical energy currency in most living cells, which is used to power many cellular reactions such as vesicle and ion transport and bioluminescence (firefly luciferase). Most ATP molecules are generated by an enzyme super-complex known as the ATP synthase, which consists of a hydrophilic F1 sub-complex and a membrane-bound FO sub-complex.

ATP synthase is one of the most important enzymes on earth and can be in all kingdoms of life from complex eukaryotes to bacteria and eubacteria as well as photosynthetic organism.

This unique motor can be thought of as a grinder water mill. Its F1 and membrane-bound FO domains correspond to a grinder and a waterwheel, respectively. Energy stored in an electrochemical gradient, reminiscent of water current, is physically converted into rotation by a proton motive force through the waterwheel- shaped FO domain. The rotation of the FO domain drives movements of the central stalk (transmission box) in response to conformational changes in the grinder-shaped F1 domain, in which the physical energy is converted into chemical energy through the condensation of ADP and Pi to ATP. The electrochemical gradient is generated by the respiratory chain complex in mitochondria or the photosynthetic reaction center in chloroplasts.

However, details of the ATP synthase complex structure remain limited. The elucidation of these details using single-particle cryogenic electron microscopy (cryo-EM) may shed light on these mechanisms and aid in understanding how structural changed relate to its coupling to ATP synthesis.

Project Leader: Jay-How Yang

One of the four classes of reaction centers (RCs), the Type I anoxygenic RC, is found in an organism called Heliobacterium modesticaldum which is isolated from volcanic soils in Iceland. Their RC-antenna complex, hereafter referred to as the heliobacterial photosystem (HbP), was not well-understood until our recently collaboration that led to an X-ray crystal structure at 2.2 angstrom-resolution. We are currently using X-ray crystallography to understand various structural aspects of the HbP which gives insight into how photosynthesis evolved from an anoxygenic atmosphere on Earth.

Project Leader: Raimund Fromme

This project aims to overcome damage to PSII under high light by replacing it with artificial water splitting catalysts powered by solar electricity, where chemical mediators shuttle electrons and protons into the organism within electrochemical cells (instead of from PSII). The goal is to improve photosynthetic efficiency, especially at high light, and convert solar electricity into high energy fuels.

Project Leader: Christine Lewis