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Molecule ‘Moves’ to Protect Against Too Much Sun

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A team led by Cheryl Kerfeld, the Hannah Distinguished Professor of Structural Bioengineering in the Michigan State University-DOE Plant Research Lab, has documented that one molecule within a photosynthesis-producing bacteria can “move” to dissipate extra energy from overexposure to sunlight.

In a recent paper published in Science, the team discovered that in cyanobacteria, an energy-quenching mechanism is triggered by an unprecedented, large-scale (relatively speaking) shift of a single carotenoid pigment within a protein. Ryan Leverenz (above, right), the paper’s lead author, first identified the movement of the carotenoid.

“Now that we’ve identified how this molecular switch works, we can potentially fine-tune the process in order to improve cyanobacteria’s viability as a biofuel,” Leverenz said.

How it works

Through photosynthesis, plants are able to harvest solar energy and convert it to chemical energy. However, overexposure to sunlight is damaging to natural photosynthetic systems of green plants and cyanobacteria, and it is also expected to be damaging to artificial photosynthetic systems that are being developed.

Nature has solved the problem through a photoprotection mechanism called “nonphotochemical-quenching.” This allows solar energy to be safely dissipated as heat from one molecular system to another.

Translocation of the carotenoid pigment within a critical light-sensitive protein called the Orange Carotenoid Protein triggers a shifting of the protein from the light-absorbing orange state to the energy-quenching red state, providing cyanobacteria with protection from too much sunlight. Image credit: Berkeley Center for Structural Biology

Kerfield’s team found that translocation of the carotenoid pigment within a critical light-sensitive protein called the Orange Carotenoid Protein triggers a shifting of the protein from the light-absorbing orange state to the energy-quenching red state, providing cyanobacteria with protection from too much sunlight.

Designing artificial photosynthesis

According to Kerfield,who is also an affiliate of the Physical Biosciences Division at Lawrence Berkeley National Laboratory, creating an efficient artificial version of photosynthesis would realize the dream of solar power as the ultimate green and renewable source of electrical energy.

“Prior to our work, the assumption was that carotenoids are static, held in place by the protein scaffold,” Kerfeld said. “Having shown that the translocation of carotenoid within the protein is a functional trigger for photoprotection, scientists will need to revisit other carotenoid-binding protein complexes to see if translocation could play a role in those systems as well.

“Understanding the dynamic function of carotenoids should be useful for the design of future artificial photosynthetic systems.”

This research was supported by the DOE Office of Science.

The full release can be found at http://newscenter.lbl.gov/2015/06/26/orange-is-the-new-red/.

– Photo above: Emily Pawlowski, technical aide; Cheryl Kerfeld, Hannah Distinguished Professor of biochemistry and molecular biology; Ryan Leverenz, research assistant.

 

 

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