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Hydrogen Bonding Environment of the N3–H Group of Flavin Mononucleotide in the Light Oxygen Voltage Domains of Phototropins

Iwata, Tatsuya, Nozaki, Dai, Yamamoto, Atsushi, Koyama, Takayuki, Nishina, Yasuzo, Shiga, Kiyoshi, Tokutomi, Satoru, Unno, Masashi, Kandori, Hideki
Biochemistry 2017 v.56 no.24 pp. 3099-3108
Adiantum, Arabidopsis, Fourier transform infrared spectroscopy, blue light, hydrogen bonding, mutants, optogenetics, photoreceptors, proteins, temperature
The light oxygen voltage (LOV) domain is a flavin-binding blue-light receptor domain, originally found in a plant photoreceptor phototropin (phot). Recently, LOV domains have been used in optogenetics as the photosensory domain of fusion proteins. Therefore, it is important to understand how LOV domains exhibit light-induced structural changes for the kinase domain regulation, which enables the design of LOV-containing optogenetics tools with higher photoactivation efficiency. In this study, the hydrogen bonding environment of the N3–H group of flavin mononucleotide (FMN) of the LOV2 domain from Adiantum neochrome (neo) 1 was investigated by low-temperature Fourier transform infrared spectroscopy. Using specifically ¹⁵N-labeled FMN, [1,3-¹⁵N₂]FMN, the N3–H stretch was identified at 2831 cm–¹ for the unphotolyzed state at 150 K, indicating that the N3–H group forms a fairly strong hydrogen bond. The N3–H stretch showed temperature dependence, with a shift to lower frequencies at ≤200 K and to higher frequencies at ≥250 K from the unphotolyzed to the intermediate states. Similar trends were observed in the LOV2 domains from Arabidopsis phot1 and phot2. By contrast, the N3–H stretch of the Q1029L mutant of neo1-LOV2 and neo1-LOV1 was not temperature dependent in the intermediate state. These results seemed correlated with our previous finding that the LOV2 domains show the structural changes in the β-sheet region and/or the adjacent Jα helix of LOV2 domain, but that such structural changes do not take place in the Q1029L mutant or neo1-LOV1 domain. The environment around the N3–H group was also investigated.