June 27, 2015

Orange is the New Red

Berkeley Lab Study Shows Orange Carotenoid Protein Shifts More Than Just Color for Cyanobacterial Photoprotection

(June 27, 2015)  Overexposure to sunlight, which is damaging to natural photosynthetic systems of green plants and cyanobacteria, is also expected to be damaging to artificial photosynthetic systems. Nature has solved the problem through a photoprotection mechanism called “nonphotochemical-quenching,” in which excess solar energy is safely dissipated as heat from one molecular system to another. With an eye on learning from nature’s success, a team of Berkeley Lab researchers has discovered a surprising key event in this energy-quenching process.

In a study led by Cheryl Kerfeld, a structural biologist with Berkeley Lab’s Physical Biosciences Division, the research team found that in cyanobacteria the energy-quenching mechanism is triggered by an unprecedented, large-scale movement (relatively speaking) from one location to another of the carotenoid pigment within a critical light-sensitive protein called the Orange Carotenoid Protein (OCP). As a result of this translocation, the carotenoid changes its shape slightly and interacts with a different set of amino acid neighbors causing the protein to shift from an “orange” light-absorbing state to a “red” photoprotective state. This turns out to be an unanticipated molecular priming event in photoprotection.

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