The results suggest an involvement of Psb35 in the life cycle of cyanobacterial Chl-binding proteins, especially CP47. Nevertheless, in comparison with WT, the Psb35-less mutant showed an accelerated pigment bleaching during prolonged dark incubation. The absence of Psb35 led to a lower accumulation and decreased stability of the CP47 antenna module and associated high-light-inducible proteins but did not change the growth rate of the cyanobacterium under the variety of light regimes. In addition, the Psb35 co-purified with a large unique complex of CP47 and photosystem I trimer. However, the isolated Psb35-PSIIs were enriched with auxiliary PSII assembly factors like Psb27, Psb28-1, Psb28-2 and RubA while they lacked the lumenal proteins stabilizing the PSII oxygen-evolving complex. Using this pulldown assay, we showed that the Psb35 remains attached to CP47 after the integration of CP47 into PSII complexes. This protein was named Psb35 and its presence in the CP47 module was confirmed by the isolation of FLAG-tagged version of Psb35. PCC 6803 and found that it contains a 11-kDa protein encoded by the ssl2148 gene. We isolated the CP47 antenna module from the cyanobacterium Synechocystis sp. Each such module consists of one large chlorophyll (Chl)-binding protein, number of small membrane polypeptides, pigments and other cofactors.
The biogenesis of PSII is a complicated process that involves a coordinated linking of assembly modules in a precise order. Photosystem II (PSII) is a large membrane protein complex performing primary charge separation in oxygenic photosynthesis.