Heliorhodopsin Evolution Is Driven by Photosensory Promiscuity in Monoderms
Paul-Adrian Bulzu, Vinicius Silva Kavagutti, Maria-Cecilia Chiriac, Charlotte D. Vavourakis, Keiichi Inoue, Hideki Kandori, Adrian-Stefan Andrei, Rohit Ghai
Abstract
Heliorhodopsins are enigmatic, novel rhodopsins with a membrane orientation that is opposite to all known rhodopsins. However, their cellular and ecological functions are unknown, and even their taxonomic distribution remains a subject of debate. We provide evidence that HeRs are a novel type of sensory rhodopsins linked to histidine kinases and other two-component system genes across phyla boundaries. In support of this, we also identify two novel putative signal transducing domains in HeRs that are fused with them. We also observe linkages of HeRs to genes involved in mitigation of light-induced oxidative stress and increased carbon and nitrogen metabolism. Finally, we synthesize these findings into a framework that connects HeRs with the cellular response to light in monoderms, activating light-induced oxidative stress defenses along with carbon/nitrogen metabolic circuitries. These findings are consistent with the evolutionary, taxonomic, structural, and genomic data available so far.