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Dr.
David M. Kramer (chair)
.jpg) 509-335-4964
dkramer@wsu.edu
Professor,
Institute of Biological Chemistry. Professor of Molecular Plant
Sciences. Ph.D. 1990, University of Illinois at Urbana-Champaign.
Research
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 QO 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 (qE) 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 QO 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 QO-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 QO 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.
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