![]() Type-2 animal rhodopsins function as G-protein-coupled receptors, while the molecular functions of type-1 microbial rhodopsins are highly diverse and include light-driven ion pumps, light-gated ion channels, light sensors, and light-activated enzymes. Rhodopsins are classified into type-1 microbial and type-2 animal rhodopsins, which contain all- trans and 11- cis retinal, respectively. Many organisms perceive light using rhodopsins ( Ernst et al., 2014 Govorunova et al., 2017 Grote et al., 2014 Rozenberg et al., 2021), integral membrane proteins containing retinal chromophores. The neuronal activity generated by V2HeR3 suggests that it can potentially be used as an optogenetic tool, similarly to type-1 microbial rhodopsins. huxleyi cell membranes, only V2HeR3 has the potential to depolarize the host cells by light, possibly to overcome the host defense mechanisms or to prevent superinfection. Except for V2HeR3 from EhV-202, none of these proteins exhibit ion transport activity. huxleyi contain one HeR that is related to the viral HeRs, while its viruses EhV-201 and EhV-202 contain two and three HeRs, respectively. Three environmental viral HeRs from the same group as well as a more distantly related HeR exhibited similar proton-transport activity, indicating that HeR functions might be diverse similarly to type-1 microbial rhodopsins. ![]() E205 and E215 form a PAG of the Schiff base, and mutations at these positions converted the protein into an outward proton pump. Site-directed mutagenesis study revealed that E191 in TM6 constitutes the gate together with the retinal Schiff base. V2HeR3 absorbs blue-green light, and the active intermediate contains the deprotonated retinal Schiff base. Here, we report that a viral HeR from Emiliania huxleyi virus 202 (V2HeR3) is a light-activated proton transporter. Heliorhodopsins (HeRs), a recently discovered new rhodopsin family, are widely present in archaea, bacteria, unicellular eukaryotes, and giant viruses, but their function remains unknown. ![]() Rhodopsins convert light into signals and energy in animals and microbes. ![]()
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