PsbX maintains efficient electron transport in Photosystem II and reduces susceptibility to high light in Synechocystis sp. PCC 6803

• Published in: Biochimica et biophysica acta. Bioenergetics Vol. 1863; no. 2; p. 148519
• Main Authors: Biswas, Sandeep, Eaton-Rye, Julian J.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.02.2022
• Subjects: Acceptor side; Bacterial Proteins - metabolism; Bicarbonate; Bioenergetics; Cyanobacteria; Electron Transport; Light; Low-molecular-weight proteins; Photosynthesis; Photosystem II Protein Complex - metabolism; Plastoquinone - analogs & derivatives; Plastoquinone - metabolism; Synechocystis - metabolism; Thylakoids - metabolism; F; O, J, I and P; PS II; QA; DCBQ; QB; Bicarbonate; Bis-Tris; Bioenergetics; Cyanobacteria; SDS; BN-PAGE; Fm; Fo; BG-11; OEC; D1; D2; CP47; Tris; Low-molecular-weight proteins; PCC; CP43; HEPES; LMW; ROS; DCMU; DMBQ; S states; Acceptor side; Photosynthesis
• ISSN: 0005-2728; 1879-2650; 1879-2650
• DOI: 10.1016/j.bbabio.2021.148519

PsbX is a 4.1 kDa intrinsic Photosystem II (PS II) protein, found together with the low-molecular-weight proteins, PsbY and PsbJ, in proximity to cytochrome b559. The function of PsbX is not yet fully characterized but PsbX may play a role in the exchange of the secondary plastoquinone electron acceptor QB with the quinone pool in the thylakoid membrane. To study the role of PsbX, we have constructed a PsbX-lacking strain of Synechocystis sp. PCC 6803. Our studies indicate that the absence of PsbX causes sensitivity to high light and impairs electron transport within PS II. In addition to a change in the QB-binding pocket, PsbX-lacking cells exhibited sensitivity to sodium formate, suggesting altered binding of the bicarbonate ligand to the non-heme iron between the sequential plastoquinone electron acceptors QA and QB. Experiments using 35S-methionine revealed high-light-treated PsbX-lacking cells restore PS II activity during recovery under low light by an increase in the turnover of PS II-associated core proteins. These labeling experiments indicate the recovery after exposure to high light requires both selective removal and replacement of the D1 protein and de novo PS II assembly. •PsbX is essential for maintaining PS II activity under high light.•Absence of PsbX impacts forward electron transport.•Removing PsbX causes changes in bicarbonate binding to PS II.•Recovery after high-light exposure involves de novo PS II assembly.