On the long roster of essential biological processes, few, if any, are more important than photosynthesis, which converts sunlight to chemical energy. All plants use photosynthesis to obtain the energy they need to live, and all animals, in turn, harvest the energy they need — directly or indirectly — from plants.
The way plants, algae, and some bacteria harness energy from the sun to produce food is a marvel of biology, and not all the details of the process are well understood. But between 1982 and 1985, Johann Deisenhofer, working in collaboration with Robert Huber and Hartmut Michel at Germany's Max Planck Institute for Biochemistry, helped resolve the pathway by which sunlight is converted to chemical energy. The accomplishment earned Deisenhofer and his colleagues the 1988 Nobel Prize in Chemistry. Earlier in the same year, Deisenhofer became an HHMI investigator at the University of Texas Southwestern Medical Center.
Photosynthesis is initiated in plants as sunlight is captured by chlorophyll, the pigment that gives plants their green color. Chlorophyll is sequestered in organelles called chloroplasts, also home to the plant's protein reaction center. There, sunlight is transformed into chemical energy as chlorophyll molecules eject electrons, pumping energy from one protein to another.
In 1982, using Rhodopseudomonas viridis, a purple bacterium capable of photosynthesis, Michel grew crystals of the microbe's photosynthetic reaction center. The reaction center is an aggregate of proteins located in the membrane of the bacterial cell. Proteins from the reaction center initiate the process of converting sunlight to chemical energy.
Over the next three years, Deisenhofer and Michel, using x-ray crystallography, constructed a detailed, atom-by-atom picture of the protein complex. At the time, it was the largest such complex to be characterized. The arrangement of the more than 10,000 atoms of the photosynthetic reaction center's protein complex provided the blueprint scientists needed to further understanding of how the sun's energy is transformed into the chemical energy necessary for much of life on Earth. The feat led to a general understanding of the mechanisms of photosynthesis and a more detailed understanding of how the process works in bacteria. It also enabled a more thorough comparison of the similarities and differences between the photosynthetic processes of bacteria and plants.
Deisenhofer's work has implications far beyond the theoretical understanding of photosynthesis. Its potential has already been realized in agriculture to help develop crop plants resistant to the herbicides that shut down the photosynthetic capabilities of weeds. Importantly, the work fueled new insight into the biology of cell membranes, the all-important interface between cells and the outside world. That knowledge, and the methods used to obtain it, promises a better understanding of how diseases affect cells and how those diseases might be treated.
Finally, by providing a window to the highly efficient processes plants and other organisms use to gather energy from the sun, the work may help improve the design of solar panels and other technologies that humans use to do the same.
Photo: Reid Horn