Abstract
The PsbT subunit of cyanobacterial photosystem II (PSII) is a membrane-spanning α-helix of ∼3.5 kDa positioned at the PSII dimer interface with each monomer contributing a copy. Removal of PsbT, as a result of interrupting the psbT gene in Synechocystis sp. PCC 6803, reduced the rate of electron transfer between QA and QB and these ΔPsbT cells were susceptible to photodamage. However, the extent of photodamage depended upon the electron acceptor and was severe in the presence of the PSII-specific electron acceptor dimethyl-p-benzoquinone (DMBQ) but minimal when whole chain electron transport was measured in the presence of bicarbonate. Here we show formate and DMBQ cause a slowing of QA− oxidation in ΔPsbT cells and this effect is reversed, in part, by the addition of bicarbonate. These results indicate that PsbT plays an important role in the architecture of the acceptor side of PSII and affects the ligand environment of the non-heme iron and the binding environment of DMBQ.