Influence of the Protein Environment on the Regulation of the Photosystem II Activity — A Time-Resolved Fluorescence Study

Abstract

The early photosynthetic processes taking place in Photosystem II (PSII), charge separation and electron transfer, can be regulated in many ways, amongst which the intrinsic properties and the internal dynamics of particular cofactors in the electron transfer chain as well as their interactions with the surrounding proteins play a significant role. We compare the time-resolved fluorescence of the dimeric cyanobacterial (Thermosynechococcus elongatus) Photosystem II core particles isolated from WT and from cells expressing only the psbA3 gene product. The D1 protein of the PS II reaction center (RC) is present in three different copies in cyanobacteria: PsbA1, PsbA2 and PsbA3. In the investigated PSII particles the two former genes were knocked-out, resulting in the overexpression of the psbA3 gene, which is not present under physiological light conditions. The psbA3 gene product differs from PsbA1 in over ten amino acid residues, some positioned close to the early electron transfer chain cofactors. The influence of this amino acid alteration, in particular the interaction between the active pheophytin Pheo_D1 and the D1-130 residue (glutamine/glutamate), on the primary events was investigated in PSII particles with the RCs in either the open or closed state. We are particularly interested in possible changes of the protein dynamics coupled to charge separation.