start-ver=1.4 cd-journal=joma no-vol=58 cd-vols= no-issue=26 article-no= start-page=2934 end-page=2943 dt-received= dt-revised= dt-accepted= dt-pub-year=2019 dt-pub=20190531 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Photochemical Characterization of a New Heliorhodopsin from the Gram-Negative Eubacterium Bellilinea caldifistulae (BcHeR) and Comparison with Heliorhodopsin-48C12 en-subtitle= kn-subtitle= en-abstract= kn-abstract= Many microorganisms express rhodopsins, pigmented membrane proteins capable of absorbing sunlight and harnessing that energy for important biological functions such as ATP synthesis and phototaxis. Microbial rhodopsins that have been discovered to date are categorized as type-1 rhodopsins. Interestingly, researchers have very recently unveiled a new microbial rhodopsin family named the heliorhodopsins, which are phylogenetically distant from type-1 rhodopsins. Among them, only heliorhodopsin-48C12 (HeR-48C12) from a Gram-positive eubacterium has been photochemically characterized [Pushkarev, A., et al. (2018) Nature 558, 595-599]. In this study, we photochemically characterize a purple-colored heliorhodopsin from Gram-negative eubacterium Bellilinea caldifistulae (BcHeR) as a second example and identify which properties are or are not conserved between BcHeR and HeR-48C12. A series of photochemical measurements revealed several conserved properties between them, including a visible absorption spectrum with a maximum at around 550 nm, the lack of ion-transport activity, and the existence of a second-order O-like intermediate during the photocycle that may activate an unidentified biological function. In contrast, as a property that is not conserved, although HeR-48C12 shows the light adaptation state of retinal, BcHeR showed the same retinal configuration under both dark- and light-adapted conditions. These comparisons of photochemical properties between BcHeR and HeR-48C12 are an important first step toward understanding the nature and functional role of heliorhodopsins. en-copyright= kn-copyright= en-aut-name=ShibukawaAtsushi en-aut-sei=Shibukawa en-aut-mei=Atsushi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=KojimaKeiichi en-aut-sei=Kojima en-aut-mei=Keiichi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=NakajimaYu en-aut-sei=Nakajima en-aut-mei=Yu kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=NishimuraYosuke en-aut-sei=Nishimura en-aut-mei=Yosuke kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= en-aut-name=YoshizawaSusumu en-aut-sei=Yoshizawa en-aut-mei=Susumu kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=5 ORCID= en-aut-name=SudoYuki en-aut-sei=Sudo en-aut-mei=Yuki kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=6 ORCID= affil-num=1 en-affil=Graduate School of Medicine, Dentistry and Pharmaceutical Sciences , Okayama University kn-affil= affil-num=2 en-affil=Graduate School of Medicine, Dentistry and Pharmaceutical Sciences , Okayama University kn-affil= affil-num=3 en-affil=Atmosphere and Ocean Research Institute , The University of Tokyo kn-affil= affil-num=4 en-affil=Atmosphere and Ocean Research Institute , The University of Tokyo kn-affil= affil-num=5 en-affil=Atmosphere and Ocean Research Institute , The University of Tokyo kn-affil= affil-num=6 en-affil=Graduate School of Medicine, Dentistry and Pharmaceutical Sciences , Okayama University kn-affil= END