The N-terminal sequence of the extrinsic PsbP protein modulates the redox potential of Cyt b559 in photosystem II

Abstract

The PsbP protein, an extrinsic subunit of photosystem II (PSII) in green plants, is known to induce a conformational change around the catalytic Mn4CaO5 cluster securing the binding of Ca2+ and Cl– in PSII. PsbP has multiple interactions with the membrane subunits of PSII, but how these affect the structure and function of PSII requires clarification. Here, we focus on the interactions between the N-terminal residues of PsbP and the α subunit of Cytochrome (Cyt) b559 (PsbE). A key observation was that a peptide fragment formed of the first N-terminal 15 residues of PsbP, ‘pN15’, was able to convert Cyt b559 into its HP form. Interestingly, addition of pN15 to NaCl-washed PSII membranes decreased PSII’s oxygen-evolving activity, even in the presence of saturating Ca2+ and Cl– ions. In fact, pN15 reversibly inhibited the S1 to S2 transition of the OEC in PSII. These data suggest that pN15 can modulate the redox property of Cyt b559 involved in the side-electron pathway in PSII. This potential change of Cyt b559, in the absence of the C-terminal domain of PsbP, however, would interfere with any electron donation from the Mn4CaO5 cluster, leading to the possibility that multiple interactions of PsbP, binding to PSII, have distinct roles in regulating electron transfer within PSII.

Selective nitration of PsbO1, PsbO2, and PsbP1 decreases PSII oxygen evolution and photochemical efficiency in intact leaves of Arabidopsis

“…However, no X-ray crystallographic data are available to support our hypothetical model of involvement of tyrosine residues of PsbO1 or PsbO2 in photosynthetic electron transport. No crystal structures of higher-plant PSIIs are currently available; consequently, the binding locations of extrinsic proteins in PSII remain elusive 8 . The minimal possible distance between PsbO and manganese atoms in the water oxidation center of PSII in thermophilic cyanobacteria is 15-20 A .…”

“…By contrast, PsbP1 is involved in electron transfer within PSII. 8,9 The N-terminal residues of PsbP1 and cytochrome (Cyt) b 559 (PsbE) are involved in a side-electron pathway, or secondary electron transport pathway that regulates the oxygen-evolving activity of PSII as described above. The side-electron pathway is distinct from the primary electron-transport pathway leading to oxidization of water and plastoquinone reduction, and its main function is to protect PSII from photoinhibition.…”

“…This pathway functions as a safety valve to remove the excess oxidative hole on the donor side. [8][9][10][11] The details of this side-electron pathway are still unclear. [8][9][10][11] PsbP1 plays a distinct role in the side-electron pathway.…”

“…[8][9][10][11] The details of this side-electron pathway are still unclear. [8][9][10][11] PsbP1 plays a distinct role in the side-electron pathway. 8 Moreover, various interactions between PsbP1 and PSII reportedly play important roles in regulating the electron transfer reactions in PSII.…”

“…[8][9][10][11] PsbP1 plays a distinct role in the side-electron pathway. 8 Moreover, various interactions between PsbP1 and PSII reportedly play important roles in regulating the electron transfer reactions in PSII. 8 By contrast, the role of PsbO in the side-electron pathway is unknown.…”