A photoactive carotenoid protein acting as light intensity sensor
Résumé
Intense sunlight is dangerous for photosynthetic organisms.
Cyanobacteria, like plants, protect themselves from light-induced stress
by dissipating excess absorbed energy as heat. Recently, it was
discovered that a soluble orange carotenoid protein, the OCP, is
essential for this photoprotective mechanism. Here we show that the OCP
is also a member of the family of photoactive proteins; it is a unique
example of a photoactive protein containing a carotenoid as the
photoresponsive chromophore. Upon illumination with blue-green light,
the OCP undergoes a reversible transformation from its dark stable
orange form to a red "active" form. The red form is essential for the
induction of the photoprotective mechanism. The illumination induces
structural changes affecting both the carotenoid and the protein. Thus,
the OCP is a photoactive protein that senses light intensity and
triggers photoprotection.
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