Psb28 Protein Is Involved in the Biogenesis of the Photosystem II Inner Antenna CP47 (PsbB) in the Cyanobacterium Synechocystis sp. PCC 6803    

Abstract

The role of the Psb28 protein in the structure and function of the photosystem II (PSII) complex has been studied in the cyanobacterium Synechocystis sp. PCC 6803. The protein was localized in the membrane fraction and, whereas most of the protein was detected as an unassembled protein, a small portion was found in the PSII core complex lacking the CP43 antenna (RC47). The association of Psb28 with RC47 was further confirmed by preferential isolation of RC47 from the strain containing a histidine-tagged derivative of Psb28 using nickel-affinity chromatography. However, the affinity-purified fraction also contained a small amount of the unassembled PSII inner antenna CP47 bound to Psb28-histidine, indicating a structural relationship between Psb28 and CP47. A psb28 deletion mutant exhibited slower autotrophic growth than wild type, although the absence of Psb28 did not affect the functional properties of PSII. The mutant showed accelerated turnover of the D1 protein, faster PSII repair, and a decrease in the cellular content of PSI. Radioactive labeling revealed a limitation in the synthesis of both CP47 and the PSI subunits PsaA/PsaB in the absence of Psb28. The mutant cells contained a high level of magnesium protoporphyrin IX methylester, a decreased level of protochlorophyllide, and released large quantities of protoporphyrin IX into the medium, indicating inhibition of chlorophyll (Chl) biosynthesis at the cyclization step yielding the isocyclic ring E. Overall, our results show the importance of Psb28 for synthesis of Chls and/or apoproteins of Chl-binding proteins CP47 and PsaA/PsaB.

Regulatory factors for the assembly of thylakoid membrane protein complexes

“…In psb28 null mutants, the functional properties of PSII are not affected but synthesis of CP47 and PSI subunits PsaA and PsaB is reduced. In addition, inactivation of Psb28 results in inhibition of chlorophyll synthesis at the cyclization step, which suggests that Psb28 functions in regulating the synthesis of chlorophylls [31]. A Psb28 homologue is also found in the Arabidopsis genome but its role remains elusive.…”

Subunit Organization of a Synechocystis Hetero-Oligomeric Thylakoid FtsH Complex Involved in Photosystem II Repair

“…To delete the wild-type copy of the ftsH3 (slr1604) gene, a linear deletion construct was prepared replacing most of the ftsH3 gene (nucleotides 161 to 1691) with an erythromycin resistance cassette using a megaprimer PCR method as described by Dobáková et al (2009). This construct containing 600 bp upstream and downstream regions of the ftsH3 gene with the erythromycin resistance cassette (obtained from plasmid pPV142 of Staphylococcus simulans) in the middle was constructed in two steps using long fusion primers complementary to the ftsH3 gene in one direction and the erythromycin resistance cassette in the other.…”

PsbN Is Required for Assembly of the Photosystem II Reaction Center in Nicotiana tabacum

“…LPA2 and LPA3 cooperate with each other and interact with ALB3 in assisting incorporation and stabilization of CP43 (Ossenbühl et al, 2004;Cai et al, 2010). Psb28 was suggested to be important for the synthesis of chlorophylls and/or apoproteins of the inner antenna subunit CP47 (Dobáková et al, 2009). Owing to the highly conserved structure of PSII, the functions of most assembly factors have already been established in cyanobacteria and still persist in plant chloroplasts, although the corresponding mutants in plants generally display much stronger phenotypes.…”