ИСТИНА

To protect themselves from the high intensity of solar radiation cyanobacteria use watersoluble photoactive protein, Orange Carotenoid Protein (OCP). It is responsible for a photoactive triggering of the of non-photochemical quenching (NPQ). OCP converts in to quenching red form under blue-green illumination,. Functional analogue of the red active form can be obtained by chemical activation with high concentrations of sodium thiocyanate (NaSCN). In this work, we show that Purple Carotenoid Protein (PCP), which was obtained by single replacement of tryptophan-288 on alanine, interacts with the phycobilisomes and causes non-photochemical quenching. The effect is comparable to the quenching induced by OCP activated by blue-green light. We used variety of optical methods to compare different forms of OCP and their ability to induce NPQ. Data obtained by Raman spectroscopy suppose that carotenoid conformation is sensitive to the structure of the C-domain. Combination of differential scanning fluorimetry (DSC) and picosecond time-resolved fluorescence anisotropy measurements allowed us to compare the stability of different OCP forms and to estimate relative differences in protein size. We assume that PCP is a promising model of permanently active and stable red form of OCP, which does not require photoactivation to induce NPQ.