Characterization of Chlamydomonas voltage-gated calcium channel and its interaction with photoreceptor support VGCC modulated photobehavioral response in the green alga.

Calcium (Ca) signaling plays a major role in regulating multiple processes in living cells. The photoreceptor potential in Chlamydomonas triggers the generation of all or no flagellar Ca currents that cause membrane depolarization across the eyespot and flagella. Modulation in membrane potential causes changes in the flagellar waveform, and hence, alters the beating patterns of Chlamydomonas flagella. The rhodopsin-mediated eyespot membrane potential is generated by the photoreceptor Ca current or P-current however, the flagellar Ca currents are mediated by unidentified voltage-gated calcium (VGCC or CaV) and potassium channels (VGKC). The voltage-gated ion channel that associates with ChRs to generate Ca influx across the flagella and its cellular distribution has not yet been identified. Here, we identified putative VGCCs from algae and predicted their novel properties through insilico analysis. We further present experimental evidence on Chlamydomonas reinhardtii VGCCs to predict their novel physiological roles. Our experimental evidences showed that CrVGCC4 localizes to the eyespot and flagella of Chlamydomonas and associates with channelrhodopsins (ChRs). Further in silico interactome analysis of CrVGCCs suggested that they putatively interact with photoreceptor proteins, calcium signaling, and intraflagellar transport components. Expression analysis indicated that these VGCCs and their putative interactors can be perturbed by light stimuli. Collectively, our data suggest that VGCCs in general, and VGCC4 in particular, might be involved in the regulation of the photobehavioral response of Chlamydomonas.

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