The bacterial counterparts of plant phototropins

We review and analyze the growing family of bacterial proteins carrying the LOV (light oxygen voltage) motif, a flavin-binding photoactive domain first characterized in plant blue-light receptors, the phototropins. A total of 29 sequences encoding LOV-proteins can be detected in the genomes of 24 bacterial species. In the bacterial LOV domains, the majority of the amino acids known to interact with the flavin mononucleotide (FMN) chromophore in phototropin LOVs are conserved, supporting the suggestion of their possible role as blue-light sensors. The Bacillus subtilis protein YtvA has been the first bacterial LOV-protein shown to bind FMN and to undergo the same light-induced reactions as plant phototropins. The photocycle involves the reversible formation of a covalent adduct between FMN and a conserved cysteine. In this work we report preliminary results on a Caulobacter crescentus LOV-kinase, that undergoes the same photochemistry as YtvA. The bacterial LOV-proteins exhibit a variety of effector domains associated to the light-responsive LOV-domain, e.g. histidine kinase, transcriptional regulators, putative phosphodiesterases and regulators of stress factors, pointing to their physiological role as sensing and signalling proteins.