Different Role of the Jα Helix in the Light-Induced Activation of the LOV2 Domains in Various Phototropins

Phototropins (phot) are blue light receptors in plants which are involved in phototropism, stomatal opening, and chloroplast movements. Phototropin has two LOV domains (LOV I and LOV2), and the LOV2 domain is responsible for activation of Ser/Thr kinase. There is an alpha-helix at the C-terminal side of the LOV2 domain, which is called the J alpha helix. The functional importance of the J alpha helix has been established for Arabidopsis phot1, where light-induced structural perturbation takes place in the J alpha helix during the photocycle of LOV2 domains. However, the present FTIR study reports a different role of the J alpha helix in light-induced signal transduction of LOV2 domains, Here we construct LOV2 domains with (LOW-J alpha) and without (LOV-core) the J alpha helix for Arabidopsis phot1 and phot2 and Adiantum neochrome I and compare their light-Induced difference FTIR spectra. Light-induced protein structural changes differ significantly between LOV-J alpha and LOV-core for Arabidopsis phot1 [Yamamoto, A., Iwata, T., Sato, Y., Matsuoka, D., Tokutomi, S., and Kandori, H. (2009) Biophys. J. 96, 2771-2778]. fit contrast, the difference spectra are identical between LOV-J alpha and LOV-core for Adiantum neochrome 1. In Arabidopsis phot2, the protein structural changes are intermediate between Arabidopsis phot I and Adiantum neochrome 1. These results suggest that the conformational changes of the J alpha helix and the interaction between the LOV-core and the J alpha helix are different among phototropins. The role of the J alpha helix for signal transduction in phototropins is discussed.