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Title: Proton exit pathways surrounding the oxygen evolving complex of photosystem II

Journal Article · · Biochimica et Biophysica Acta - Bioenergetics

Photosystem II allows water to be the primary electron source for the photosynthetic electron transfer chain. Water is oxidized to dioxygen at the Oxygen Evolving Complex (OEC), a Mn4CaO5 inorganic core embedded on the lumen side of PSII. Water-filled channels surrounding the OEC must bring in substrate water molecules, remove the substrate protons to the lumen, and may transport the product oxygen. Three water-filled channels, denoted large, narrow, and broad, extend from the OEC towards the aqueous surface more than 15 Å away. However, the role of each pathway in the transport in and out of the OEC is yet to be established. Here, we combine Molecular Dynamics (MD), Multi Conformation Continuum Electrostatics (MCCE) and Network Analysis to compare and contrast the three potential proton transfer paths. Hydrogen bond network analysis shows that near the OEC the waters are highly interconnected with similar free energy for hydronium at all locations. The paths diverge as they move towards the lumen. The water chain in the broad channel is better connected than in the narrow and large channels, where disruptions in the network are observed approximately 10 Å from the OEC. In addition, the barrier for hydronium translocation is lower in the broad channel. Furthermore, a proton released from any location on the OEC can access all paths, but the likely exit to the lumen passes through PsbO via the broad channel.

Research Organization:
Yale Univ., New Haven, CT (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC05-00OR22725; FG02-05ER15646; DESC0001423; SC0001423
OSTI ID:
1879124
Alternate ID(s):
OSTI ID: 1812296; OSTI ID: 1815094
Journal Information:
Biochimica et Biophysica Acta - Bioenergetics, Journal Name: Biochimica et Biophysica Acta - Bioenergetics Vol. 1862 Journal Issue: 8; ISSN 0005-2728
Publisher:
ElsevierCopyright Statement
Country of Publication:
Netherlands
Language:
English

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