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).