Proton transfer pathway from the oxygen-evolving complex in photosystem II substantiated by extensive mutagenesis

Structural dynamics in the water and proton channels of photosystem II during the S2 to S3 transition

“…The Cl1 channel has been proposed as a proton release pathway during the S 2 to S 3 transition in many studies in the literature 26 , 54 , 55 , 61 , and our current structural observation prefers this assignment. We observe structural changes around D1-E65, D2-E312, and D1-R334 at 150 μs after the 2nd flash, which are reversed by 250 μs.…”

“…6 and described in the following. In the S 2 -state, D1-E65 and D2-E312 share a proton as indicated by the short H-bonding distance of around 2.5 Å and confirmed by simulations 55 . This suggests that in the S 2 -state and up to 50 µs after the 2nd flash (2 F(50µs)), the Cl1 channel is in a ‘closed state’ for proton egress, since D1-E65 is H-bonded to D1-N335, which is inert to a Grotthuss proton hopping mechanism, and D1-R334 is H-bonded to W119, functioning with its positive charge as a directional barrier (Figs.…”

“…This rearrangement forms an ‘open state’ for an effective proton transfer to the other side of the bottleneck. The proton transfer from the protonated D1-D61 to a deprotonated D1-E65 or E312 was recently reported to be exothermic via one or two waters 55 . This implies that E65-E312 can accept a proton from the OEC only after releasing a proton towards the bulk (Fig.…”

“…The low barrier proton release of W1 via D1-D61 was suggested from the DFT calculations for the S 2 to S 3 transition 65 . Also, the role of D1-E65 and D1-D61 in the proton release has been widely discussed 20 , 27 , 35 , 46 , 54 , 55 , 59 , 66 – 69 . The new conformation of D1-E65/E312 with W119 forms an ‘open state’ for proton release towards the bulk by 150 µs (Fig.…”

Mechanism of the formation of proton transfer pathways in photosynthetic reaction centers

“…Although Asp-H124, His-H126, and His-H128 are likely to form the entry point of the major PT pathway (12), it also seems plausible that the PT pathway is delocalized toward the protein bulk surface (13)(14)(15). The delocalization of the PT pathway is also observed in PSII; specifically, the PT pathway is branched as it proceeds from the oxygen-evolving complex via D1-Asp61 toward the protein bulk surface (16).…”