Oral Presentations
March 5th (Tue), 2019

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Animal opsins: non-visual functions and optogenetic applications

Akihisa Terakita and Mitsumasa Koyanagi
Department of Biology and Geoscience, Graduate School of Science, Osaka City University,Osaka, Japan; OCARINA, Osaka City University, Osaka, Japan

Most animal opsins bind to a retinal as a chromophore to form photosensitive pigments
and serve as light-sensitive G protein-coupled receptors (GPCRs), which constitute a large
protein family of receptors that sense molecules outside the cell and activate inside signaltransduction pathways and, ultimately, generate cellular responses.
Many animals capture light through opsin-based pigments and utilize the light informationfor visual and non-visual functions including regulation of circadian rhythms. Thousands ofopsins have been identified from a wide variety of animas thus far. We have characterized
diverse opsins, including novel ones, spectroscopically, biochemically, molecularphysiologically and evolutionally [1-4], and also investigated their contribution to biological
function [5, 6]. Interestingly, we found that some non-visual opsins have unique molecularproperties and such unique peroperties might be suitable for optogenetics applications, which
are the combination of genetics and optics to control well-defined events within specific cellsof living tissues.
In lower vertebrates, pineal and its related organs in the brain discriminate UV and visible
light. A pineal UV-sensitive opsin, parapinopsin has been considered to be involved in thiscolor discrimination [1, 3]. We recently found that a signle photoreceptor cell containing
parapinopsin alone generates color opponency, which is essential cellular photoresponse todetect different wavelenght of lights [6]. Because it has been discussed that maltiple opsins
are requiered for color opponency, this finding could propse a new concept for the mechanismof color detection and its evolution. We also found that UV and green light illuminations
activate and deactivate parapinopsin, respectively to regulate G protein-mediated signaltransduction cascade in the mammalian cultured cells [7]. Therefore we suggest thatparapinopsin has optogenetic potentials to control cellular responses and animal behaviours ina light wavelength-dependent manner.

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References:[1] Koyanagi, Kawano et al., Proc. Natl. Acad. Sci. U.S.A 2004, 101, 6687 [2] Koyanagi etal., Proc. Natl. Acad. Sci. U.S.A 2013, 110, 4998 [3] Koyanagi, Wada et al., BMC Biology
2015, 17, 73 [4] Gerrard et al., Proc. Natl. Acad. Sci. U.S.A 2018, 115, 6201-6206[5] Nagata et al., Science 2012, 355, 469 [6] Wada et al., Proc. Natl. Acad. Sci. U.S.A 2018,110, 4998
[7] Kawano-Yamashita et al., PLoS One 2015, 10, e0141280

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New insights on ChlD1 function in Photosystem IIfrom site-directed mutants
Miwa SugiuraProteo-Science Research Center, Ehime University, Bunkyo-cho,Matsuyama, Ehime 790-8577, Japan.
The monomeric chlorophyll, ChlD1, which is located between the PD1PD2 chlorophyll
pair and the pheophytin, PheoD1, is the longest wavelength chlorophyll in the heart ofPhotosystem II and is thought to be the primary electron donor. Its central Mg2+ is liganded toa water molecule that is H-bonded to D1/T179 [1]. Here, site-directed mutants on D1/T179H
and D1/T179V, were made in the thermophilic cyanobacterium, Thermosynechococcus
elongatus, and characterized by a range of biophysical techniques [2]. The Mn4CaO5 clusterin the water-splitting site is fully active in both mutants. Changes in thermoluminescenceindicate that i) radiative recombination occurs via the repopulation of *ChlD1 itself; ii)
non-radiative charge recombination reactions appeared to be faster in the T179H-PSII; and iii)
the properties of PD1PD2 were unaffected by this mutation, and consequently iv) the immediate
precursor state of the radiative excited state is the ChlD1+PheoD1- radical pair. Chlorophyll
bleaching due to high intensity illumination correlated with the amount of 1O2 generated.
Comparison of the bleaching spectra with the electrochromic shifts attributed to ChlD1 upon
QA- formation, indicates that in the T179H-PSII and in the WT*3-PSII, the ChlD1 itself is thechlorophyll that is first damaged by 1O2, whereas in the T179V-PSII a more red chlorophyll isdamaged, the identity of which is discussed. Thus, ChlD1 appears to be one of the primarydamage site in recombination-mediated photoinhibition. Finally, changes in the absorption ofChlD1 very likely contribute to the well-known electrochromic shifts observed at ~430 nm
during the S-state cycle.

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References:[1] Umena, Y.; Kawakami, K.; Shen, J.–R.; Kamiya, N. Nature 2011, 473 55.
[2] Takegawa, Y.; Nakamura, M.; Nakamura, S.; Noguchi, T.; Sellés, J.; Rutherford, A.W.;
Boussac, A.; Sugiura, M. Biochem. Biophys. Acta 2019, 1860 297.

19I-220Light Conversion in Bacterial PhotosynthesisJian-Ping Zhang
Department of Chemistry, Renmin University of China, Beijing 100872, P. R.
China
Abstract: In bacterial photosynthesis, light harvesting antennae and reaction centers are
responsible for harnessing sunlight. The photosynthetic bacterium Thermochromatium (Tch.)
tepidum is a thermophile growing at optimal temperature of 48−50 ºC. Its light harvesting
antennae exhibit remarkable thermal stability and nearinfrared absorption. It is important tostudy the primary excitation dynamics of both isolated and membrane-embedded lightharvesting complexes of Tch. tepidum, so as to understand the mechanisms of light absorption,
thermal stability, photoprotection and resistance to environmental stresses.
We have investigated, by the use of triplet excitation profiles (TEPs),[1] the roles ofmulti-compositional carotenoids (Cars) in the core light harvesting complexes (m-LH1-RCs)from a mutant strain of Rhodobacter (Rba.) sphaeroides.[2] Transient absorption kinetics
revealed the triplet excitation transfer from spheroidene (Spe, major composition∼85%) tospirilloxanthin (Spx, minor composition ∼8%), implying that the two different kinds of Cars
coexist in individual m-LH1-RC complexes. TEP results showed that Spx is involved inphotoprotection by quenching 3BChl*, whereas Spe does so merely for BChls of relatively
low site energy. The Spe-to-Spx triplet excitation transfer and their inequivalence inquenching 3BChl* constitute a mechanism of cooperative photoprotection.
We have also investigated, by the using femtosecond time-resolved absorption spectroscopy,
the uphill excitation energy transfer (EET) from the core antennae (LH1s) to the reaction
centers (RCs) by comparing the m-LH1-RC to the native LH1-RC of Tch. tepidum. TheI-3

former exhibits a substantially large RC-LH1 energy difference (∆E = 630 cm−1, ∼3kBT). The
semilogarithmic plot of the EET rate is found to be invresely proportional to ∆E, which
consolidates a thermal activation mechanism for the uphill EET. The results are discussed on
the basis of the newly reported LH1-RC structure of Tch. tepidum,[3] which allows us topropose the presence of specific doorway BChls in LH1 in promoting the uphill EET.
References:[1] Yu J., Fu L.-M., Yu L.-J., Shi Y., Wang P., Wang-Otomo Z.-Y., Zhang J.-P. J. Am. Chem.
Soc. 2017, 139, 15984.
[2] Nagashima, K. V., Sasaki, M., Hashimoto, K., Takaichi, S., Nagashima, S., Yu, L.-J., Abe,Y., Gotou, K., Kawakami, T., Takenouchi, M. Proc. Natl. Acad. Sci. U. S. A. 2017, 114,10906.
[3] Niwa, S.; Yu, L.-J.; Takeda, K.; Hirano, Y.; Kawakami, T.; Wang-Otomo, Z.-Y.; Miki, K.
Nature, 2014, 508, 228.

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