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

High-light-inducible proteins (Hlips) are single-helix transmembrane proteins that are essential for the survival of cyanobacteria under stress conditions. The model cyanobacterium Synechocystis sp. PCC 6803 contains four Hlip isoforms (HliA-D) that associate with Photosystem II (PSII) during its assembly. HliC and HliD are known to form pigmented (hetero)dimers that associate with the newly synthesized PSII reaction center protein D1 in a configuration that allows thermal dissipation of excitation energy. Thus, it is expected that they photoprotect the early steps of PSII biogenesis. HliA and HliB, on the other hand, bind the PSII inner antenna protein CP47, but the mode of interaction and pigment binding have not been resolved. Here, we isolated His-tagged HliA and HliB from Synechocystis and show that these two very similar Hlips do not interact with each other as anticipated, rather they form HliAC and HliBC heterodimers. Both dimers bind Chl and β-carotene in a quenching conformation and associate with the CP47 assembly module as well as later PSII assembly intermediates containing CP47. In the absence of HliC, the cellular levels of HliA and HliB were reduced, and both bound atypically to HliD. We postulate a model in which HliAC-, HliBC-, and HliDC-dimers are the functional Hlip units in Synechocystis. The smallest Hlip, HliC, acts as a 'generalist' that prevents unspecific dimerization of PSII assembly intermediates, while the N-termini of 'specialists' (HliA, B or D) dictate interactions with proteins other than Hlips.

• Klíčová slova
• CP47, Chlorophyll, High-light-inducible proteins, Photosystem II, Synechocystis,
• MeSH
• bakteriální proteiny metabolismus   MeSH
• fotosystém II (proteinový komplex) metabolismus   MeSH
• protein TNFSF14 metabolismus   MeSH
• světlosběrné proteinové komplexy * metabolismus   MeSH
• Synechocystis * metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriální proteiny MeSH
• fotosystém II (proteinový komplex) MeSH
• protein TNFSF14 MeSH
• světlosběrné proteinové komplexy * MeSH

Life on Earth depends on photosynthesis, the conversion of light energy into chemical energy. Plants collect photons by light harvesting complexes (LHC)-abundant membrane proteins containing chlorophyll and xanthophyll molecules. LHC-like proteins are similar in their amino acid sequence to true LHC antennae, however, they rather serve a photoprotective function. Whether the LHC-like proteins bind pigments has remained unclear. Here, we characterize plant LHC-like proteins (LIL3 and ELIP2) produced in the cyanobacterium Synechocystis sp. PCC 6803 (hereafter Synechocystis). Both proteins were associated with chlorophyll a (Chl) and zeaxanthin and LIL3 was shown to be capable of quenching Chl fluorescence via direct energy transfer from the Chl Qy state to zeaxanthin S1 state. Interestingly, the ability of the ELIP2 protein to quench can be acquired by modifying its N-terminal sequence. By employing Synechocystis carotenoid mutants and site-directed mutagenesis we demonstrate that, although LIL3 does not need pigments for folding, pigments stabilize the LIL3 dimer.

• MeSH
• chlorofyl metabolismus   MeSH
• karotenoidy metabolismus   MeSH
• multimerizace proteinu MeSH
• mutace MeSH
• přenos energie MeSH
• proteiny chloroplastové chemie   genetika   metabolismus   MeSH
• proteiny huseníčku chemie   genetika   metabolismus   MeSH
• sbalování proteinů MeSH
• Synechocystis genetika   metabolismus   MeSH
• vazba proteinů MeSH
• xanthofyly metabolismus   MeSH
• zeaxanthiny genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chlorofyl MeSH
• ELIP2 protein, Arabidopsis MeSH Prohlížeč
• karotenoidy MeSH
• light-harvesting-like protein 3, Arabidopsis MeSH Prohlížeč
• proteiny chloroplastové MeSH
• proteiny huseníčku MeSH
• violaxanthin MeSH Prohlížeč
• xanthofyly MeSH
• zeaxanthiny MeSH