First Evidence for Phototropin-Related Blue-Light Receptors in Prokaryotes

Abstract

A prokaryotic protein, YtvA from Bacillus subtilis, was found to possess a light, oxygen, voltage (LOV) domain sharing high homology with the photoactive, flavin mononucleotide (FMN)-binding LOV domains of phototropins (phot), blue-light photoreceptors for phototropism in higher plants. Computer-based three-dimensional modeling suggests that YtvA-LOV binds FMN in a similar pocket as phot-LOVs. Recombinant YtvA indeed exhibits the same spectroscopical features and blue-light-induced photochemistry as phot-LOVs, with the reversible formation of a blue-shifted photoproduct, assigned to an FMN-cysteine thiol adduct (Thio 383 ). By means of laser-flash photolysis and time-resolved optoacoustic experiments, we measured the quantum yield of formation for Thio 383 , ⌽ Thio ϭ 0.49, and the enthalpy change, ⌬H Thio ϭ 135 kJ/mol, with respect to the parent state. The formation of Thio 383 is accompanied by a considerable volume contraction, ⌬V Thio ϭ Ϫ13.5 ml/mol. Similar to phot-LOVs, Thio 383 is formed from the decay of a red-shifted transient species, T 650 , within 2 s. In both YtvA and free FMN, this transient has an enthalpy content of ϳ200 kJ/mol, and its formation is accompanied by a small contraction, ⌬V T Ϸ Ϫ1.5 ml/mol, supporting the assignment of T 650 to the FMN triplet state, as suggested by spectroscopical evidences. These are the first studies indicating that phototropin-related, blue-light receptors may exist also in prokaryotes, besides constituting a steadily growing family in plants.

Enhancement of a σB-dependent stress response in Bacillus subtilis by light via YtvA photoreceptor

“…1B). These results are consistent with the result of Losi et al (2002), and indicating that the LOV domain of YtvA senses blue light.…”

Lactococcus lactis Thioredoxin Reductase Is Sensitive to Light Inactivation

“…There are several established examples of photoexcited flavoproteins that function as photoreceptors of blue light, 48 for example, YtvA from B. subtilis. 49 It could also be suggested that inactivation of TrxR results in an oxidized thiol redox environment that activates redox-sensitive transcription factors such as Spx. 50 In general, blue light at wavelengths of ≤470 nm has an antibacterial effect.…”

Blue Light Perception in Plants

“…The FMN binding modules belong to the PAS (PER/ARNT/ SIM) domain superfamily (15,16) occurring in many regulatory proteins and have been designated as LOV 1 domains; the acronym is based on the involvement in the signaling of light, oxygen, or voltage levels (10,17). Very recently, the presence of a LOV domain with similarity to the photoactive LOV domains of the phototropin of higher plants has been identified in the non-photosynthetic soil bacterium Bacillus subtilis (18).…”