Photo-ion mobility mass spectrometry for investigating the structural dynamics of photoreceptor proteins Alex Jones 1 , Ines Camacho 1 , Bruno Bellina 2 , Alina Theisen 2 , Rachelle Black 2 , Rennart Ramakers 2 , Perdita Barran 2 1 National Physical Laboratory, UK, 2 The University of Manchester, UK Proteins adopt a dizzying array of functions in nature. Such versatility is enabled, and function fine-tuned, by dynamic variations in protein structure, which can evolve through a functional cycle. Photoreceptor proteins are no exception. Typically, a bound chromophore absorbs light, which results in structural changes in the protein that transduce a signal. Functions vary from shade avoidance to circadian photoentrainment, and increasingly photoreceptors are being reengineered as optogenetic tools to enable optical control of a given biological system with high spatiotemporal precision. To understand better a protein’s function, or to optimise a protein-based tool, it is vital to understand their structural dynamics. This remains a significant challenge, however, especially if regions of intrinsic disorder are important to function. In recent years, we have developed native ion mobility mass spectrometry techniques with which to investigate structural dynamics in photoreceptor proteins. 1-3 Using illumination in the ion source, we have been able to activate the proteins prior to desolvation and measure the resulting structural changes, with some surprising results. References 1. Camacho, I. S.; Black, R.; Heyes, D. J.; Johannissen, L. O.; Ramakers, L. A. I.; Bellina, B.; Barran, P. E.; Hay, S.; Jones, A. R. Interplay between chromophore binding and domain assembly by the B12-dependent photoreceptor protein, CarH. Chem. Sci. 2021, 12 , 8333. 2. Camacho, I. S.; Theisen, A.; Johannissen, L. O.; Díaz-Ramos, L. A.; Christie, J. M.; Jenkins, G. I.; Bellina, B.; Barran, P.; Jones, A. R. Native mass spectrometry reveals the conformational diversity of the UVR8 photoreceptor. Proc. Natl. Acad. Sci. USA 2019, 116 (4), 1116. 3. Kutta, R. J.; Hardman, S. J. O.; Johannissen, L. O.; Bellina, B.; Messiha, H. L.; Ortiz-Guerrero, J. M.; Elias-Arnanz, M.; Padmanabhan, S.; Barran, P.; Scrutton, N. S.et al. The photochemical mechanism of a B 12 -dependent photoreceptor protein. Nat Commun 2015, 6 , 7907.
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