Gary Brudvig
Benjamin Silliman Professor of ChemistryCards
About
Research
Overview
What is the molecular basis for energy transduction in plant photosynthesis? This is the question that has been the focus of our research program. The first step in the energy-transduction process is the light-induced charge-separation reaction that occurs in a membrane-protein complex called the photoreaction center. Thereafter, a series of rapid electron-transfer reactions serve to stabilize the charge-separated state. Later still, the photochemically-produced oxidant and reductant are consumed in the oxidation of water and the reduction of carbon dioxide. One of the primary targets of our research is the plant enzyme called photosystem II that catalyzes the oxidation of water to dioxygen at a site within the enzyme containing a tetranuclear manganese cluster. Photosystem II is one of two reaction center complexes that initiate the light-driven electron transfer reactions of plant photosynthesis. The long-term objective of our research is to develop an understanding at the molecular level of the conversion of light energy into chemical energy in plant photosynthesis. Toward this goal, we are pursuing several related lines of research. A major effort involves biophysical studies of the purified photosystem II complex itself. We use spectroscopic and biophysical methods to probe the structure of the redox centers, the kinetics and yields of electron-transfer reactions, and the chemistry of water oxidation in photosystem II. Our aim is to define how Nature has solved the difficult problem of the efficient light-driven, four-electron oxidation of water to O2. It is hoped that these studies will provide insight into the design of artificial systems that split water. Toward this goal, we are also investigating inorganic models of the manganese site in photosystem II. Because the model complexes are more easily characterized, the inorganic studies provide important information that can aid the interpretation of results from the biological system. On the other hand, the information from the biophysical studies better define the nature of the catalytic manganese complex that is to be modeled. The synergism between the inorganic and biological chemistry is an important aspect of this research. A third area of research is artificial photosynthesis. We are working to develop artificial processes that use solar energy for fuel production in collaboration with Professors Batista, Crabtree and Schmuttenmaer. Our aim is to use a bioinspired approach for solar fuel production based on our water-oxidation catalysts attached to nanostructured TiO2.
Biophysical Studies of Photosystem II
We use EPR, optical,
and Raman spectroscopy, turnover measurements of oxygen evolution and
site-directed mutagenesis to monitor the photochemical events and to
obtain structural and mechanistic information on photosystem II.
Photosystem II contains more than ten distinct redox-active centers.
One of these is the tetranuclear manganese cluster that, together with
a redox-active tyrosine (Yz), catalyzes the oxidation of water. We
study photosystem II samples that are prepared and trapped at low
temperature in each of the oxidation states ("S-states") of the
manganese complex. The binding and reactions of substrates and
inhibitors are also studied in order to define the structure and
chemical properties of the manganese cluster as it proceeds through the
catalytic cycle. For example, acetate competes with chloride for
binding to the manganese cluster. Illumination of PSII treated with
acetate inhibits the enzyme in a state in which a paramagnetic S-state
(S2) of the manganese cluster interacts with oxidized Yz. We have
investigated this interaction using EPR and used the spectroscopic
results in conjunction with spectral simulations and molecular modeling
to devise a proposed structure for the manganese cluster and its
associated cofactors (calcium, chloride, and Yz). In order to control
the turnover of photosystem II in the highly concentrated samples
needed for spectroscopic studies, we have used herbicides that bind to
photosystem II and block electron transfer. One recent extension of
this approach involves tethering a redox-active center to the herbicide
so that multi-electron turnover control can be achieved. Other projects
involve the use of optical or fluorescence spectroscopy to study the
electron-transfer reactions that occur during the water oxidation
cycle. We have also used Raman spectroscopy to characterize the
oxidized forms of some of the electron-transfer cofactors, such as
chlorophyll and carotenoid cation radicals, and also the manganese
complex itself. Photosystem II contains several redox centers,
including cytochrome b559, that do not play a direct role in the
reactions leading to water oxidation. The function of these species is
currently not well understood, but they may be involved in protection
of photosystem II from photodamage. By using a combination of
spectroscopic measurements, functional assays and site-directed
mutagenesis, we are working to reveal how these alternate electron
donors function.
Inorganic Models of the Manganese Cluster in Photosystem II
The S states in the water oxidation cycle are different oxidation
states of the tetranuclear manganese cluster. The chemistry of this
manganese cluster involves high-valent manganese and H2O. The goal of
inorganic modeling studies is to give an insight into the high-valent
Mn chemistry in aqueous media that may be relevant to the
photoactivated assembly of the tetranuclear manganese cluster, its
structure and physical properties, and the mechanism of water
oxidation. We have synthesized the first di-mu-oxo Mn-complex capable of
catalytically forming O2 from O-atom transfer reagents such as oxone
(HSO5-). EPR, low-temperature optical and Raman spectroscopy, magnetics
and electrochemistry are some of the methods that we use to
characterize the manganese complexes.
Medical Subject Headings (MeSH)
Academic Achievements and Community Involvement
Links & Media
News
- January 06, 2020
Discovery potluck
- February 19, 2019
Nine From Medical School Are Among 13 Yale Faculty Named to Connecticut Academy of Science and Engineering
- September 04, 2012
Yale's Brudvig to head new Energy Sciences Institute at West Campus