Functional Analysis of the Channel Rhodopsin Genes from the Green Algae of the White Sea Basin

Optogenetics as the method of light-controlled regulation of cellular processes is based on the use of the channel rhodopsins that directly generate photoinduced currents. The largest number of channel rhodopsin genes has been identified in the green microalgae Chlorophyta, and the demand for increasing the number of functionally characterized channel rhodopsins and the diversity of their photochemical parameters keeps growing. We performed the expression analysis of cation channel rhodopsin (CCR) genes in natural isolates of microalgae of the genera Haematococcus and Bracteacoccus from the unique Polar Circle region. The identified full-length CCR transcript of H. lacustris is the product of alternative splicing and encodes the Hl98CCR2 protein with no photochemical activity. The 5′-partial fragment of the B. aggregatus CCR transcript encodes the Ba34CCR protein containing a conserved TM1–TM7 membrane domain and a short cytosolic fragment. Upon heterologous expression of the TM1–TM7 fragment in CHO-K1 cell culture, light-dependent current generation was observed, and its parameters correspond to the characteristics of the CCR. The first discovered functional channel rhodopsin of Bracteacoccus has no close CCR homologs and may be of interest as a candidate for optogenetics.