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.

• MeSH
• bakteriální proteiny fyziologie   MeSH
• delece genu MeSH
• fotosystém II - proteinový komplex biosyntéza   genetika   metabolismus   MeSH
• mutace MeSH
• světlosběrné proteinové komplexy nedostatek   metabolismus   MeSH
• Synechocystis genetika   fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• fotosystém II - proteinový komplex MeSH
• photosystem II, chlorophyll-binding protein, CP-47 MeSH Prohlížeč
• světlosběrné proteinové komplexy MeSH

The selective replacement of photodamaged D1 protein within the multisubunit photosystem II (PSII) complex is an important photoprotective mechanism in chloroplasts and cyanobacteria. FtsH proteases are involved at an early stage of D1 degradation, but it remains unclear how the damaged D1 subunit is recognized, degraded, and replaced. To test the role of the N-terminal region of D1 in PSII biogenesis and repair, we have constructed mutants of the cyanobacterium Synechocystis sp PCC 6803 that are truncated at the exposed N terminus. Removal of 5 or 10 residues blocked D1 synthesis, as assessed in radiolabeling experiments, whereas removal of 20 residues restored the ability to assemble oxygen-evolving dimeric PSII complexes but inhibited PSII repair at the level of D1 degradation. Overall, our results identify an important physiological role for the exposed N-terminal tail of D1 at an early step in selective D1 degradation. This finding has important implications for the recognition of damaged D1 and its synchronized replacement by a newly synthesized subunit.

• MeSH
• autotrofní procesy účinky léků   účinky záření   MeSH
• biologické modely MeSH
• dimerizace MeSH
• fluorescenční spektrometrie MeSH
• fotosystém II - proteinový komplex chemie   metabolismus   MeSH
• linkomycin farmakologie   MeSH
• molekulární sekvence - údaje MeSH
• mutace genetika   MeSH
• mutantní proteiny metabolismus   MeSH
• podjednotky proteinů chemie   metabolismus   MeSH
• posttranslační úpravy proteinů * účinky léků   účinky záření   MeSH
• sekundární struktura proteinů MeSH
• sekvence aminokyselin MeSH
• světlo MeSH
• Synechocystis cytologie   účinky léků   metabolismus   účinky záření   MeSH
• tylakoidy účinky léků   metabolismus   účinky záření   MeSH
• vztahy mezi strukturou a aktivitou MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fotosystém II - proteinový komplex MeSH
• linkomycin MeSH
• mutantní proteiny MeSH
• podjednotky proteinů MeSH