Deletion of psbJ leads to accumulation of Psb27–Psb28 photosystem II complexes in Thermosynechococcus elongatus

The life cycle of Photosystem II (PSII) is embedded in a network of proteins that guides the complex through biogenesis, damage and repair. Some of these proteins, such as Psb27 and Psb28, are involved in cofactor assembly for which they are only transiently bound to the preassembled complex. In this work we isolated and analyzed PSII from a ΔpsbJ mutant of the thermophilic cyanobacterium Thermosynechococcus elongatus. From the four different PSII complexes that could be separated the most prominent one revealed a monomeric Psb27–Psb28 PSII complex with greatly diminished oxygen-evolving activity. The MALDI-ToF mass spectrometry analysis of intact low molecular weight subunits (< 10 kDa) depicted wild type PSII with the absence of PsbJ. Relative quantification of the PsbA1/PsbA3 ratio by LC-ESI mass spectrometry using 15N labeled PsbA3-specific peptides indicated the complete replacement of PsbA1 by the stress copy PsbA3 in the mutant, even under standard growth conditions (50 μmol photons m− 2 s− 1). This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

► Psb27–Psb28 PSII complexes accumulate in a psbJ deletion mutant of T. elongatus.
► MALDI-ToF-MS analysis of intact low molecular weight subunits resembles wildtype PSII.
► The D1 copy PsbA1 is completely replaced by the stress copy PsbA3 in the mutant.