509-335-4964 dkramer@wsu.edu

Professor, Institute of Biological Chemistry
Chair, Molecular Plant Sciences

Ph.D.1990, University of Illinois at Urbana-Champaign

Research Interests

Energetics and control of photosynthesis; electron transfer reactions; coupling of electron transfer reactions to proton pumping and to ATP synthesis; evolution of bioenergetics; photosynthesis in extreme environments.

My laboratory seeks to understand how plants convert light energy into forms usable for life, how these processes function at both molecular and physiological levels, how they are regulated and controlled, how they define the energy budget of plants and the ecosystem and how they have adapted through evolution to support life in extreme environments. Some of the specific project are outlined below.

The multiple roles of the thylakoid proton motive force. Energy conversion by the chloroplast involves capture of light energy and its funneling through a series of pigment excited states, electron and proton transfer reactions, ultimately into the NADP+/NADPH and ATP/ADP + Pi couples. In this way, photosynthesis drives essentially all biochemistry in our ecosystem. Many of the intermediates in energy conversion are also quite reactive, and at sufficiently high concentrations they can destroy the photosynthetic apparatus (photoinhibition or photodamage) or even kill the plant. In order to prevent photoinhibition, the efficiency of the light harvesting complexes is down-regulated via the dumping of excitation energy harmlessly as heat. This, of course, lowers the efficiency of photosynthesis, but prevents photodamage. There are strong indications that the balancing of photoprotection and photochemical efficiency is important for
acclimation to environmental challenges. We are focusing on the dual role of the transthylakoid proton gradient, or proton motive force (pmf), which serves a pivotal role in this balancing act, both as a key intermediate in energy conversion, driving the synthesis of ATP, as well as the trigger for initiation of NPQ. New research on the structure and function of the ATP synthase and the cytochrome b6f complex, as well as on the nature of the proton motive force, has begun to reveal how pmf balances these two key roles.

The mechanisms of the electron transfer-coupled proton pumps. In order to make ATP, the chloroplast couples exergonic electron transfer reactions to translocation of protons across the thylakoid membrane. The resulting pmf is used to drive the endergonic synthesis of ATP. We have focused on the reactions of the cytochrome b6f complex, and related cytochrome bc1 complexes (of bacteria and mitochondria). These enzymes oxidize hydroquinones (quinols) and reduce
soluble electron carriers. The energy released in this process is used to pump protons, probably via a mechanism called a Q-cycle, which is responsible to producing about 1/3rd of all of the ATP in plants. Under adverse conditions, the cytochrome b6f/bc1 complexes can also produce, as a byproduct, superoxide, which in turn can lead to diseases, including some associated with aging in humans. In order to understand (and potentially control) these processes, we are
investigating the molecular structure and mechanism of these complexes using a range of biophysical and molecular techniques.

Proton-coupled electron transfer reactions in energy conversion. It has been shown that key reactions in these complexes are a special type of electron transfer reaction, called a proton-coupled electron transfer reaction (PCET). Although applicable theory exists for straightforward electron transfer (ET), PCET is much more complex. We have been investigating PCET using a synthetic photoactive mimic of the Qo site of the cytochrome bc1 and b6f complexes.

How photosynthesis works in vivo. Ultimately, we aim to understand how the specific molecular mechanisms of the photosynthetic system determine how the plant survives and grows. This approach is enabled by our development of novel spectroscopic techniques that allow us to observe specific photosynthetic reactions in both in isolated systems (which are easily manipulated), and in living plants. With these tools, we are now able to monitor many of the photosynthesis reactions in living plants under natural conditions. This allows us to test whether models developed on isolated systems truly operate in vivo. In some cases, such studies have led us to new conclusions about how enzymes operate at the molecular level. Finally, this technology developed in these efforts has potential applications in plant breeding and precision farming, by giving growers ability to rapidly assess the physiological status of plants.

Selected publications

Cape, J.L., Bowman, M.K. and Kramer, D.M. 2006. Understanding the cytochrome bc complexes by what they don’t do. The Q-cycle at 30. Trends in Plant Science 11:46-55.

Cape, J.L., Bowman, M.K. and Kramer, D.M. 2006. Computation of the redox and protonation properties of quinones: Towards the prediction of redox cycling natural products. Phytochemistry 67(16):1781-1788.

Forquer, I., Covian, R., Bowman, M.K., Trumpower, B. and Kramer, D.M. 2006. Similar transition states mediate the Q-cycle and superoxide production by the cytochrome bc₁ complex. J Biol Chem 281(50):38459-38465.

Takizawa, K., Cruz, J. A., and Kramer, D. M. 2005. In "Photosynthesis: Fundamental Aspects to Global Perspectives", van der Est, A., and Bruce, D., Eds. pp 573-575, ACG Publishing, Lawrence, KA.

Ivanov, B., Asada, K., Kramer, D. M., and Edwards, G. E. 2005. Characterization of photosynthetic electron transport in bundle sheath cells of maize. I. Ascorbate effectively stimulates cyclic electron flow around PSI. Planta 220:572-581.

Puzon, G.J., Roberts, A.G., Kramer, D.M. and Xun, L. 2005. Formation of soluble organo-chromium(III) complexes after chromate reduction in the presence of cellular organics. Environ Sci Technol 39(8):2811-2817.

Cruz, J. A., Kanazawa, A., Treff, N., and Kramer, D. M. 2005. Storage of light-driven transthylakoid proton motive force as an electric field Dy under steady-state conditions in intact cells of Chlamydomonas reinhardtii. Photosynth Res 85:221-33.

Cruz, J. A., Avenson, T. J., Kanazawa, A., Takizawa, K., Edwards, G. E., and Kramer, D. M. 2005. Plasticity in light reactions of photosynthesis for energy production and photoprotection. Journal of Experimental Botany 56:395-406.

Cape, J. L., Strahan, J. R., Lenaeus, M. J., Yuknis, B. A., Le, T. T., Shepherd, J. N., Bowman, M. K., and Kramer, D. M. 2005. The respiratory substrate rhodoquinol induces Q-cycle bypass reactions in the yeast cytochrome bc₁ Complex. Journal of Biological Chemistry 280:34654–34660.

Cape, J. L., Bowman, M. K., and Kramer, D. M. 2005. Reaction Intermediates of quinol oxidation in a photoactivatable system that mimics electron transfer in the cytochrome bc₁ complex. J Am Chem Soc 127:4208-15.

Avenson, T. J., Cruz, J. A., Kanazawa, A., and Kramer, D. M. 2005. Regulating the proton budget of higher plant photosynthesis. Proc Natl Acad Sci USA 102:9709-13.

Avenson, T. J., Kanazawa, A., Cruz, J. A., Takizawa, K., Ettinger, W. E., and Kramer, D. M. 2005. Integrating the proton circuit into photosynthesis: Progress and challenges. Plant Cell Environ 28:97-109.

Kramer, D. M., Avenson, T. J., and Edwards, G. E. 2004. Dynamic flexibility in the light reactions of photosynthesis governed by both electron and proton transfer reactions. Trends in Plant Science 9:349-357.

Kramer, D. M., Johnson, G., Kiirats, O., and Edwards, G. E. 2004. New fluorescence parameters for the determination of QA redox state and excitation energy fluxes. Photosynthesis Research 79:209-218.

Kramer, D. M., Roberts, A. G., Muller, F., Cape, J., and Bowman, M. K. 2004. Q-cycle bypass reactions at the Q_O site of the cytochrome bc₁ (and related) complexes. Methods in Enzymology 382:21-45.

Bowman, M. K., Berry, E. A., Roberts, A. G., and Kramer, D. M. 2004. Orientation of the g-factor axes of the Rieske subunit in cytochrome bc₁ complex. Biochemistry 43:430-436.

Avenson, T., Cruz, J. A., and Kramer, D. 2004. Modulation of energy dependent quenching of excitons (q_E) in antenna of higher plants. Proc Natl Acad Sci USA 101:5530-5535.

Muller, F., Roberts, A. G., Bowman, M. K., and Kramer, D. M. 2003. Architecture of the Q_O site of the cytochrome bc₁ complex probed by superoxide production. Biochemistry 41:7866-7874.

Kramer, D. M., Cruz, J. A., and Kanazawa, A. 2003. Balancing the central roles of the thylakoid proton gradient. Trends in Plant Science 8:27-32.

Muller, F., Crofts, A. R., and Kramer, D. M. 2002. Multiple Q-cycle bypass reactions at the Q_O-site of the cytochrome bc₁ complex. Biochemistry 41:7866-7874.

Kanazawa, A., and Kramer, D. M. 2002. In vivo modulation of nonphotochemical exciton quenching (NPQ) by regulation of the chloroplast ATP synthase. Proc Natl Acad Sci USA 99:12789–12794. http://www.pnas.org/cgi/reprint/182427499v1.pdf

Roberts, A., and Kramer, D. M. 2001. Inhibitor ‘double-occupancy’ in the Q_O pocket of the chloroplast cytochrome b₆f complex. Biochemistry 40:13407-13412.

Cruz, J. A., Sacksteder, C. A., Kanazawa, A., and Kramer, D. M. 2001. Contribution of electric field Dy to steady-state transthylakoid proton motive force in vitro and in vivo. Control of pmf parsing into Dy and DpH by counterion fluxes.Biochemistry 40:1226-1237.

Sacksteder, C. A., Kanazawa, A., Jacoby, M. E., and Kramer, D. M. 2000. The proton to electron stoichiometry of steady-state photosynthesis in living plants: A proton-pumping Q-cycle is continuously engaged. Proc Natl Acad Sci USA 97:14283-14288.

Sacksteder, C. A., and Kramer, D. M. 2000. Dark interval relaxation kinetics of absorbance changes as a quantitative probe of steady-state electron transfer. Photosynth. Res. 66:145-158.

Kramer, D. M., Sacksteder, C. A., and Cruz, J. A. 1999. How acidic is the lumen? Photosynthesis Research 60:151-163.