Computer Model Offers New Insight On Bacterial Photosynthesis

September 05, 1997

CHAMPAIGN, Ill. -- Using advanced computer modeling, scientists working with photosynthetic bacteria have shed light on one of Earth's most efficient photosynthetic systems.

The accomplishment, the researchers say, should boost the understanding of light absorption and energy transfer in photosynthesis -- the process that converts solar energy into chemical energy -- and eventually lead to the development of more efficient and environmentally clean energy sources.

In the August issue of the journal Physics Today, University of Illinois scientists report their successful three-dimensional computer modeling that depicts how the two light-harvesting complexes of the purple bacteria Rhodobacter sphaeroides aggregate (combine and arrange) their chlorophyll molecules in a ring around the bacteria's photosynthetic reaction center.

Creating the modeled aggregate of light-harvesting complexes 1 and 2 (LH1 and LH2) was made possible by the research team's successful determination, reported last year, of the structure of the bacteria's LH2 from Rhodospirillum molischianum by X-ray crystallography, said Xiche Hu, a postdoctoral fellow at the U. of I. Beckman Institute for Advanced Science and Technology.

The details of last year's work, in collaboration with researchers at the Max Planck Institute for Biochemistry in Frankfurt, Germany, were published in the May 1996 issue of Structure. The method used to solve the structure involved sophisticated computational modeling. A similar LH2 structure from a different species was reported in late 1995 in the journal Nature by University of Glasgow scientists, who had determined the structure with a different method.

Because purple bacteria exist in mud, they have to use what little sunlight that is unharvested by plants quickly and efficiently for their own metabolism, said Klaus Schulten, director of the Beckman's theoretical biophysics group and holder of the U. of I. Swanlund Chair in Physics. "The bacteria can store the energy captured from the sun better in a ring, because of the symmetry of the structure. "

To arrive at their model of the entire photosynthetic unit, Hu and Schulten used advanced computer simulation to combine their LH1 and LH2 models with the already known structure of the reaction center. The resulting computer model furnished a view of the ring-shaped chlorophyll aggregates of LH1 and LH2 and their efficient light-harvesting function.

"You can see that it is a beautifully engineered system," Hu said. "Learning how the chlorophylls are positioned and oriented in 3-D space is an important step toward understanding the functionality of this system."The research was funded by the National Institutes of Health, National Science Foundation and the private Carver Foundation.


University of Illinois at Urbana-Champaign

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