Light-induced structural changes of the LOV2 domains in various phototropins revealed by FTIR spectroscopy

Phototropin (Phot), a blue-light photoreceptor in plants, consists of two FMN-binding domains (named LOV1 and LOV2) and a serine/threonine (Ser/Thr) kinase domain. We have investigated light-induced structural changes of LOV domains, which lead to the activation of the kinase domain, by means of light-induced difference FTIR spectroscopy. FTIR spectroscopy revealed that the reactive cysteine is protonated in both unphotolyzed and triplet-excited states, which is difficult to detect by other methods such as X-ray crystallography. In this review, we describe the light-induced structural changes of hydrogen-bonding environment of FMN chromophore and protein backbone in Adiantum neo1-LOV2 in the C=O stretching region by use of (13)C-labeled samples. We also describe the comprehensive FTIR analysis of LOV2 domains among Arabidopsis phot1, phot2, and Adiantum neo1 with and without Jα helix domain.