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

In a study led by Cheryl Kerfeld, a structural biologist who holds joint appointments with Berkeley Lab’s Physical Biosciences Division and Michigan State University, 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.

“Prior to our work, the assumption was that carotenoids are static, held in place by the protein scaffold,” Kerfeld says. “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 as well. Understanding the dynamic function of carotenoids should be useful for the design of future artificial photosynthetic systems.”