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Instruments / Technical Area	Publication Details	Published	Actions
I03-Macromolecular Crystallography I04-Macromolecular Crystallography I23-Long wavelength MX	Light activation of Orange Carotenoid Protein reveals bicycle-pedal single-bond isomerization Volha U. Chukhutsina , James M. Baxter , Alisia Fadini , Rhodri M. Morgan , Matthew A. Pope , Karim Maghlaoui , Christian M. Orr , Armin Wagner , Jasper J. Van Thor Nature Communications 13 DOI: 10.1038/s41467-022-34137-4 Diamond Proposal Number(s): [17221] Open Access Show Abstract ▼ Abstract: Orange Carotenoid protein (OCP) is the only known photoreceptor which uses carotenoid for its activation. It is found exclusively in cyanobacteria, where it functions to control light-harvesting of the photosynthetic machinery. However, the photochemical reactions and structural dynamics of this unique photosensing process are not yet resolved. We present time-resolved crystal structures at second-to-minute delays under bright illumination, capturing the early photoproduct and structures of the subsequent reaction intermediates. The first stable photoproduct shows concerted isomerization of C9’-C8’ and C7’-C6’ single bonds in the bicycle-pedal (s-BP) manner and structural changes in the N-terminal domain with minute timescale kinetics. These are followed by a thermally-driven recovery of the s-BP isomer to the dark state carotenoid configuration. Structural changes propagate to the C-terminal domain, resulting, at later time, in the H-bond rupture of the carotenoid keto group with protein residues. Solution FTIR and UV/Vis spectroscopy support the single bond isomerization of the carotenoid in the s-BP manner and subsequent thermal structural reactions as the basis of OCP photoreception.	Oct 2022
I24-Microfocus Macromolecular Crystallography	Observation of cation chromophore photoisomerization of a fluorescent protein using millisecond synchrotron serial crystallography and infrared vibrational and visible spectroscopy James Baxter , Christopher D. M. Hutchison , Karim Maghlaoui , Violeta Cordon-Preciado , R. Marc L. Morgan , Pierre Aller , Agata Butryn , Danny Axford , Sam Horrell , Robin L. Owen , Selina L. S. Storm , Nicholas E. Devenish , Jasper J. Van Thor The Journal Of Physical Chemistry B DOI: 10.1021/acs.jpcb.2c06780 Diamond Proposal Number(s): [17221] Open Access Show Abstract ▼ Abstract: The chromophores of reversibly switchable fluorescent proteins (rsFPs) undergo photoisomerization of both the trans and cis forms. Concurrent with cis/trans photoisomerisation, rsFPs typically become protonated on the phenolic oxygen resulting in a blue shift of the absorption. A synthetic rsFP referred to as rsEospa, derived from EosFP family, displays the same spectroscopic behavior as the GFP-like rsFP Dronpa at pH 8.4 and involves the photoconversion between nonfluorescent neutral and fluorescent anionic chromophore states. Millisecond time-resolved synchrotron serial crystallography of rsEospa at pH 8.4 shows that photoisomerization is accompanied by rearrangements of the same three residues as seen in Dronpa. However, at pH 5.5 we observe that the OFF state is identified as the cationic chromophore with additional protonation of the imidazolinone nitrogen which is concurrent with a newly formed hydrogen bond with the Glu212 carboxylate side chain. FTIR spectroscopy resolves the characteristic up-shifted carbonyl stretching frequency at 1713 cm–1 for the cationic species. Electronic spectroscopy furthermore distinguishes the cationic absorption band at 397 nm from the neutral species at pH 8.4 seen at 387 nm. The observation of photoisomerization of the cationic chromophore state demonstrates the conical intersection for the electronic configuration, where previously fluorescence was proposed to be the main decay route for states containing imidazolinone nitrogen protonation. We present the full time-resolved room-temperature X-ray crystallographic, FTIR, and UV/vis assignment and photoconversion modeling of rsEospa.	Nov 2022

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