The LOV domain: a chromophore module servicing multiple photoreceptors.

Three different families of blue-light receptors have been characterized from higher plants: three cryptochromes, two phototropins, and the three members of the ZTL/ADO family. Phototropins and the ZTL/ADO proteins have chromophore modules, designated LOV domains, that bind flavin mononucleotide and undergo formation of a C(4a) flavin-cysteinyl adduct. All contain the highly conserved amino acid motif GXNCRFLQ. Over 90 prokaryote proteins also contain LOV domains with this motif upstream from one of several different functional groups. All of these that have been investigated to date act as photoreceptors in vitro and form the adduct upon irradiation. Four members of the class LOV-histidine kinase, one from a plant pathogen (Pseudomonas syringae), one from an animal pathogen Brucella melitensis), and two from a marine bacterium (Erythrobacter litoralis) respectively, mediate light-activated histidine phosphorylation. Decay of the adduct in darkness after a blue light pulse coincides with loss of the capacity for phosphorylation upon addition of ATP. At present, the biological role(s) of these light-sensitive proteins is under investigation.