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@article{aydin_probing_2025,
	title = {Probing substrate water access through the {O1} channel of {Photosystem} {II} by single site mutations and membrane inlet mass spectrometry},
	volume = {163},
	issn = {1573-5079},
	url = {https://doi.org/10.1007/s11120-025-01147-4},
	doi = {10.1007/s11120-025-01147-4},
	abstract = {Light-driven water oxidation by photosystem II sustains life on Earth by providing the electrons and protons for the reduction of CO2 to carbohydrates and the molecular oxygen we breathe. The inorganic core of the oxygen evolving complex is made of the earth-abundant elements manganese, calcium and oxygen (Mn4CaO5 cluster), and is situated in a binding pocket that is connected to the aqueous surrounding via water-filled channels that allow water intake and proton egress. Recent serial crystallography and infrared spectroscopy studies performed with PSII isolated from Thermosynechococcus vestitus (T. vestitus) support that one of these channels, the O1 channel, facilitates water access to the Mn4CaO5 cluster during its S2→S3 and S3→S4→S0 state transitions, while a subsequent CryoEM study concluded that this channel is blocked in the cyanobacterium Synechocystis sp. PCC 6803, questioning the role of the O1 channel in water delivery. Employing site-directed mutagenesis we modified the two O1 channel bottleneck residues D1-E329 and CP43-V410 (T. vestitus numbering) and probed water access and substrate exchange via time resolved membrane inlet mass spectrometry. Our data demonstrates that water reaches the Mn4CaO5 cluster via the O1 channel in both wildtype and mutant PSII. In addition, the detailed analysis provides functional insight into the intricate protein-water-cofactor network near the Mn4CaO5 cluster that includes the pentameric, near planar ‘water wheel’ of the O1 channel.},
	language = {en},
	number = {3},
	urldate = {2025-04-25},
	journal = {Photosynthesis Research},
	author = {Aydin, A. Orkun and de Lichtenberg, Casper and Liang, Feiyan and Forsman, Jack and Graça, André T. and Chernev, Petko and Zhu, Shaochun and Mateus, André and Magnuson, Ann and Cheah, Mun Hon and Schröder, Wolfgang P. and Ho, Felix and Lindblad, Peter and Debus, Richard J. and Mamedov, Fikret and Messinger, Johannes},
	month = apr,
	year = {2025},
	keywords = {CP43-V410, D1-E329, O1 channel, Oxygen evolving complex, Photosystem II, Substrate water exchange, Synechocystis sp. PCC 6803, Water delivery, Water oxidation, Water wheel},
	pages = {28},
}