2Lomonosov Moscow State University, Faculty of Biology, Biophysics Department, 119991 Moscow, Russia
3Lomonosov Moscow State University, Faculty of Biology, Biochemistry Department, 119991 Moscow, Russia
* To whom correspondence should be addressed.
Received August 21, 2017; Revision received September 11, 2017
Photoprotective mechanisms of cyanobacteria are characterized by several features associated with the structure of their water-soluble antenna complexes – the phycobilisomes (PBs). During energy transfer from PBs to chlorophyll of photosystem reaction centers, the “energy funnel” principle is realized, which regulates energy flux due to the specialized interaction of the PBs core with a quenching molecule capable of effectively dissipating electron excitation energy into heat. The role of the quencher is performed by ketocarotenoid within the photoactive orange carotenoid protein (OCP), which is also a sensor for light flux. At a high level of insolation, OCP is reversibly photoactivated, and this is accompanied by a significant change in its structure and spectral characteristics. Such conformational changes open the possibility for protein–protein interactions between OCP and the PBs core (i.e., activation of photoprotection mechanisms) or the fluorescence recovery protein. Even though OCP was discovered in 1981, little was known about the conformation of its active form until recently, as well as about the properties of homologs of its N and C domains. Studies carried out during recent years have made a breakthrough in understanding of the structural-functional organization of OCP and have enabled discovery of new aspects of the regulation of photoprotection processes in cyanobacteria. This review focuses on aspects of protein–protein interactions between the main participants of photoprotection reactions and on certain properties of representatives of newly discovered families of OCP homologs.
KEY WORDS: orange carotenoid protein, carotenoids, photoprotection, fluorescence, energy transfer, photosynthesis, phycobilisomes