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.