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

Light plays an essential role in photosynthesis; however, its excess can cause damage to cellular components. Photosynthetic organisms thus developed a set of photoprotective mechanisms (e.g., non-photochemical quenching, photoinhibition) that can be studied by a classic biochemical and biophysical methods in cell suspension. Here, we combined these bulk methods with single-cell identification of microdomains in thylakoid membrane during high-light (HL) stress. We used Synechocystis sp. PCC 6803 cells with YFP tagged photosystem I. The single-cell data pointed to a three-phase response of cells to acute HL stress. We defined: (1) fast response phase (0-30 min), (2) intermediate phase (30-120 min), and (3) slow acclimation phase (120-360 min). During the first phase, cyanobacterial cells activated photoprotective mechanisms such as photoinhibition and non-photochemical quenching. Later on (during the second phase), we temporarily observed functional decoupling of phycobilisomes and sustained monomerization of photosystem II dimer. Simultaneously, cells also initiated accumulation of carotenoids, especially ɣ-carotene, the main precursor of all carotenoids. In the last phase, in addition to ɣ-carotene, we also observed accumulation of myxoxanthophyll and more even spatial distribution of photosystems and phycobilisomes between microdomains. We suggest that the overall carotenoid increase during HL stress could be involved either in the direct photoprotection (e.g., in ROS scavenging) and/or could play an additional role in maintaining optimal distribution of photosystems in thylakoid membrane to attain efficient photoprotection.

• Klíčová slova
• Synechocystis, carotenoids, high light, microdomains, non-photochemical quenching, photoinhibition, photoprotection, photosystems, thylakoid membrane,
• MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• fotosystém I (proteinový komplex) genetika   metabolismus   MeSH
• fotosystém II (proteinový komplex) genetika   metabolismus   MeSH
• karotenoidy metabolismus   MeSH
• světlo * MeSH
• Synechocystis metabolismus   účinky záření   MeSH
• tylakoidy metabolismus   účinky záření   MeSH
• velikost buňky účinky záření   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• fotosystém I (proteinový komplex) MeSH
• fotosystém II (proteinový komplex) MeSH
• karotenoidy MeSH

Polyunsaturated lipids are important components of photosynthetic membranes. Xanthophylls are the main photoprotective agents, can assist in protection against light stress, and are crucial in the recovery from photoinhibition. We generated the xanthophyll- and polyunsaturated lipid-deficient ROAD mutant of Synechocystis sp. PCC6803 (Synechocystis) in order to study the little-known cooperative effects of lipids and carotenoids (Cars). Electron microscopic investigations confirmed that in the absence of xanthophylls the S-layer of the cellular envelope is missing. In wild-type (WT) cells, as well as the xanthophyll-less (RO), polyunsaturated lipid-less (AD), and the newly constructed ROAD mutants the lipid and Car compositions were determined by MS and HPLC, respectively. We found that, relative to the WT, the lipid composition of the mutants was remodeled and the Car content changed accordingly. In the mutants the ratio of non-bilayer-forming (NBL) to bilayer-forming (BL) lipids was found considerably lower. Xanthophyll to β-carotene ratio increased in the AD mutant. In vitro and in vivo methods demonstrated that saturated, monounsaturated lipids and xanthophylls may stabilize the trimerization of Photosystem I (PSI). Fluorescence induction and oxygen-evolving activity measurements revealed increased light sensitivity of RO cells compared to those of the WT. ROAD showed a robust increase in light susceptibility and reduced recovery capability, especially at moderate low (ML) and moderate high (MH) temperatures, indicating a cooperative effect of xanthophylls and polyunsaturated lipids. We suggest that both lipid unsaturation and xanthophylls are required for providing the proper structure and functioning of the membrane environment that protects against light and temperature stress.

• Klíčová slova
• Cyanobacteria, Lipid remodeling, Lipid-carotenoid-protein interactions, Photoinhibition, Temperature stress, Xanthophylls,
• MeSH
• beta-karoten metabolismus   účinky záření   MeSH
• buněčná membrána genetika   metabolismus   účinky záření   ultrastruktura   MeSH
• časové faktory MeSH
• fenotyp MeSH
• fotosyntéza genetika   účinky záření   MeSH
• fotosystém I (proteinový komplex) genetika   metabolismus   účinky záření   MeSH
• fyziologická adaptace MeSH
• fyziologický stres * MeSH
• genotyp MeSH
• membránové lipidy metabolismus   účinky záření   MeSH
• metabolismus lipidů genetika   účinky záření   MeSH
• mutace MeSH
• světlo * MeSH
• Synechocystis genetika   metabolismus   účinky záření   ultrastruktura   MeSH
• teplota * MeSH
• tylakoidy metabolismus   účinky záření   MeSH
• xanthofyly genetika   metabolismus   účinky záření   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• beta-karoten MeSH
• fotosystém I (proteinový komplex) MeSH
• membránové lipidy MeSH
• xanthofyly MeSH