Characterization of an unusual LOV domain protein in the alpha-proteobacterium Rhodobacter sphaeroides

The facultatively phototrophic purple bacterium Rhodobacter sphaeroides 2.4.1 harbors a LOV (light, oxygen and voltage) domain protein, which shows a particular structure. LOV domains perceive blue light by a noncovalently bound flavin and transmit the signal to various coupled output domains. Proteins, that harbor a LOV core, function e.g. as phototropins or circadian clock regulators. Jalpha helices, which act as linker between the LOV core and the output domain, were shown to be involved in the light-dependent activation of the output domain. Like PpSB2 from Pseudomonas putida, the LOV domain protein of R. sphaeroides is not coupled to an effector domain and harbors an extended C-terminal alpha helix. We expressed the R. sphaeroides LOV domain recombinantly in Escherichia coli. The protein binds an FMN as a cofactor and shows a photocycle typical for LOV domain containing proteins. In R. sphaeroides, we detected the protein as well in the cytoplasm as in the membrane fraction, which was not reported for other bacterial LOV domain proteins.