Energetics and proton release in Photosystem II fromThermosynechococcus elongatuswith a D1 protein encoded by either thepsbA2orpsbA3gene

Abstract

AbstractIn the cyanobacteriumThermosynechococcus elongatus, there are threepsbAgenes coding for the Photosystem II (PSII) D1 subunit that interacts with most of the main cofactors involved in the electron transfers. Recently, the 3D crystal structures of both PsbA2-PSII and PsbA3-PSII have been solved [Nakajima et al., J. Biol. Chem. 298 (2022) 102668.]. It was proposed that the loss of one hydrogen bond of PheD1due to the D1-Y147F exchange in PsbA2-PSII resulted in a more negativeEmof PheD1in PsbA2-PSII when compared to PsbA3-PSII. In addition, the loss of two water molecules in the Cl-1 channel was attributed to the D1-P173M substitution in PsbA2-PSII. This exchange, by narrowing the Cl-1 proton channel, could be at the origin of a slowing down of the proton release. Here, we have continued the characterization of PsbA2- PSII by measuring the thermoluminescence from the S2QA-/DCMU charge recombination and by measuring proton release kinetics using time-resolved absorption changes of the dye bromocresol purple. It was found thati) theEmof PheD1−•/PheD1was decreased by ∼ 30 mV in PsbA2-PSII when compared to PsbA3-PSII andii) the kinetics of the proton release into the bulk was significantly slowed down in PsbA2-PSII in the S2TyrZ•to S3TyrZand S3TyrZ•→ (S3TyrZ•)’ transitions. This slowing down was partially reversed by the PsbA2/M173P mutation and induced by the PsbA3/P173M mutation thus confirming a role of the D1-173 residue in the egress of protons trough the Cl-1 channel.