Nejvíce citovaný článek - PubMed ID 37986097
A thylakoid biogenesis BtpA protein is required for the initial step of tetrapyrrole biosynthesis in cyanobacteria
The biogenesis of Photosystem II is a complicated process requiring numerous auxiliary factors to assist in all steps of its assembly. The cyanobacterial protein Ycf39 forms a stress-induced complex with 2 small chlorophyll-binding, High-light-inducible proteins C and D (HliC and HliD), and has been reported to participate in the insertion of chlorophyll molecules into the central D1 subunit of Photosystem II. However, how this process is organized remains unknown. Here, we show that Ycf39 and both HliC and HliD can form distinct complexes with chlorophyll synthase (ChlG) in the model cyanobacterium Synechocystis sp. PCC 6803. We isolated and characterized ChlG complexes from various strains grown under different conditions and provide a mechanistic view of the docking of Ycf39 to ChlG via HliD and the structural role of HliC. In the absence of stress, chlorophyll is produced by the ChlG-HliD2-ChlG complex, which is stabilized by chlorophyll and zeaxanthin molecules bound to the HliD homodimer. The switch to high light leads to stress pressure and greatly elevated synthesis of HliC, resulting in the replacement of HliD homodimers with HliC-HliD heterodimers. Unlike HliD, HliC cannot interact directly with ChlG or Ycf39. Therefore, the original ChlG-HliD2-ChlG complex is converted into a ChlG-HliD-HliC hetero-trimer that presumably binds transiently to Ycf39 and the nascent D1 polypeptide. We speculate that this molecular machinery promotes the delivery of chlorophyll to D1 upon high-light-induced chlorophyll deficiency. The HliD homodimers formed under standard, nonstress growth conditions and attached to ChlG could serve as an emergency chlorophyll reserve.
- MeSH
- bakteriální proteiny * metabolismus genetika MeSH
- chlorofyl metabolismus MeSH
- fotosystém II (proteinový komplex) * metabolismus MeSH
- ligasy tvořící vazby C-O * metabolismus genetika MeSH
- světlo * MeSH
- světlosběrné proteinové komplexy MeSH
- Synechocystis * metabolismus účinky záření genetika MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- bakteriální proteiny * MeSH
- chlorofyl MeSH
- chlorophyll synthetase MeSH Prohlížeč
- fotosystém II (proteinový komplex) * MeSH
- high light-inducible protein, cyanobacteria MeSH Prohlížeč
- ligasy tvořící vazby C-O * MeSH
- světlosběrné proteinové komplexy MeSH
Epigenetic DNA modifications are pivotal in eukaryotic gene expression, but their regulatory significance in bacteria is less understood. In Synechocystis 6803, the DNA methyltransferase M.Ssp6803II modifies the first cytosine in the GGCC motif, forming N4-methylcytosine (GGm4CC). Deletion of the sll0729 gene encoding M.Ssp6803II (∆sll0729) caused a bluish phenotype due to reduced chlorophyll levels, which was reversed by suppressor mutations. Re-sequencing of 7 suppressor clones revealed a common GGCC to GGTC mutation in the slr1790 promoter's discriminator sequence, encoding protoporphyrinogen IX oxidase, HemJ, crucial for tetrapyrrole biosynthesis. Transcriptomic and qPCR analyses indicated aberrant slr1790 expression in ∆sll0729 mutants. This aberration led to the accumulation of coproporphyrin III and protoporphyrin IX, indicative of impaired HemJ activity. To confirm the importance of DNA methylation in hemJ expression, hemJ promoter variants with varying discriminator sequences were introduced into the wild type, followed by sll0729 deletion. The sll0729 deletion segregated in strains with the GGTC discriminator motif, resulting in wild-type-like pigmentation, whereas freshly prepared ∆sll0729 mutants with the native hemJ promoter exhibited the bluish phenotype. These findings demonstrate that hemJ is tightly regulated in Synechocystis and that N4-methylcytosine is essential for proper hemJ expression. Thus, cytosine N4-methylation is a relevant epigenetic marker in Synechocystis and likely other cyanobacteria.
- Klíčová slova
- DNA methyltransferase, HemJ, cyanobacteria, epigenetic modifications, tetrapyrrole biosynthesis,
- MeSH
- bakteriální proteiny metabolismus genetika MeSH
- epigeneze genetická * MeSH
- metylace DNA * MeSH
- mutace MeSH
- promotorové oblasti (genetika) * MeSH
- regulace genové exprese u bakterií MeSH
- Synechocystis * genetika metabolismus MeSH
- tetrapyrroly * metabolismus biosyntéza MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- bakteriální proteiny MeSH
- tetrapyrroly * MeSH
The growth of plants, algae, and cyanobacteria relies on the catalytic activity of the oxygen-evolving PSII complex, which uses solar energy to extract electrons from water to feed into the photosynthetic electron transport chain. PSII is proving to be an excellent system to study how large multi-subunit membrane-protein complexes are assembled in the thylakoid membrane and subsequently repaired in response to photooxidative damage. Here we summarize recent developments in understanding the biogenesis of PSII, with an emphasis on recent insights obtained from biochemical and structural analysis of cyanobacterial PSII assembly/repair intermediates. We also discuss how chlorophyll synthesis is synchronized with protein synthesis and suggest a possible role for PSI in PSII assembly. Special attention is paid to unresolved and controversial issues that could be addressed in future research.
