Deep dive into the diversity and properties of rhodopsins in actinomycetes of the family Geodermatophilaceae

Rhodopsin with the NTQ motif and heliorhodopsins, both discovered for the first time in actinomycetes of the family Geodermatophilaceae were characterized, along with characterization of the DTEW, DTEF and NDQ rhodopsins reported in members of this family previously. The identified absorption maxima ranged from 513 to 559 nm, of which the blue-shifted rhodopsin contained the NTQ motif and the red-shifted one were heliorhodopsin. An assessment of the pumping activity of the NTQ rhodopsin and heliorhodopsin showed that the former functioned as inward Cl--, Br--, I--pump with much weaker activity towards NO3-, while no any activity was detected for the later. The DTEW and DTEF rhodopsins had the outward H+-transport activity which was dependent on the presence of Ca2+ ions and on the particular E. coli expression strain. The outward pumping of H+ was also detected for NDQ rhodopsin both in NaCl and KCl solutions at pH 5 and 6, but not at pH 7. Weak Na+-efflux activity for this rhodopsin was observed at pH 6 and 7 in NaCl solution only after adding carbonyl cyanide m-chlorophenyl hydrazone (CCCP). ### Competing Interest Statement The authors have declared no competing interest. * AaClR : Alteribacter aurantiacus rhodopsin BR : bacteriorhodopsin CCCP : carbonyl cyanide m-chlorophenyl hydrazone CDS : coding sequence DDM : n-dodecyl β-D-maltoside FR : Fulvimarina pelagi rhodopsin GLR : Gillisia limnaea rhodopsin HeR : heliorhodopsins IAR : Indibacter alkaliphilus rhodopsin IPTG : isopropyl β-D-1-thiogalactopyranoside ISP2 : International Streptomyces Project-2 KR2 : Krokinobacter eikastus ( Dokdonia eikasta ) rhodopsin 2 LB : lysogeny broth NdR2 : Nonlabens dok-donensis rhodopsin 2 NM-R2 : Nonlabens marinus rhodopsin 2 NM-R3 : Nonlabens marinus rhodopsin 3 PCR : polymerase chain reaction PoClR : Parvularcula oceani rhodopsin SOE PCR : splicing by overhang extension PCR XR : xanthorhodopsin.