In oxygenic photosynthetic organisms, the light reactions are performed by protein complexes embedded in the lipid bilayer of thylakoid membranes (TMs). The organization of the bulk lipid molecules into bilayer structures provide optimal conditions for the build-up of the proton motive force (pmf) and its utilization for ATP synthesis. However, the lipid composition of TMs is dominated by the non-bilayer lipid species monogalactosyl diacylglycerol (MGDG), and functional plant TMs, besides the bilayer, contain large amounts of non-bilayer lipid phases. Bulk lipids have been shown to be associated with lumenal, stromal-side and marginal-region proteins and proposed to play roles in the self-assembly and photoprotection of the photosynthetic machinery. Furthermore, it has recently been pointed out that the generation and utilization of pmf for ATP synthesis according to the 'protet' or protonic charge transfer model Kell (Biochim Biophys Acta Bioenerg 1865(4):149504, 2024), requires high MGDG content Garab (Physiol Plant 177(2):e70230, 2025). In this study, to gain better insight into the structural and functional roles of MGDG, we employed all atom and coarse-grained molecular dynamics simulations to explore how temperature, hydration levels and varying MGDG concentrations affect the structural and dynamic properties of bilayer membranes constituted of plant thylakoid lipids. Our findings reveal that MGDG promotes increased membrane fluidity and dynamic fluctuations in membrane thickness. MGDG-rich stacked bilayers spontaneously formed inverted hexagonal phases; these transitions were enhanced at low hydration levels and at elevated but physiologically relevant temperatures. It can thus be inferred that MGDG plays important roles in heat and drought stress mechanisms.

• Klíčová slova
• Dehydration, Inverted hexagonal phase, MGDG, Non-bilayer lipid, Thylakoid membranes,
• MeSH
• fotosyntéza MeSH
• galaktolipidy metabolismus   chemie   MeSH
• lipidové dvojvrstvy metabolismus   chemie   MeSH
• simulace molekulární dynamiky * MeSH
• teplota MeSH
• tylakoidy * metabolismus   chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• galaktolipidy MeSH
• lipidové dvojvrstvy MeSH
• monogalactosyldiacylglycerol MeSH Prohlížeč

The investigation of spatial heterogeneity within the thylakoid membrane (TM) proteins has gained increasing attention in photosynthetic research. The recent advances in live-cell imaging have allowed the identification of heterogeneous organisation of photosystems in small cyanobacterial cells. These sub-micrometre TM regions, termed microdomains in cyanobacteria, exhibit functional similarities with granal (Photosystem II dominant) and stromal (Photosystem I dominant) regions observed in TM of higher plants. This study delves into microdomain heterogeneity using super-resolution Airyscan-based microscopy enhancing resolution to approximately ~125 nm in x-y dimension. The new data reveal membrane areas rich in Photosystem I within the inner TM rings. Moreover, we identified analogous dynamics in the mobility of Photosystem II and phycobilisomes; countering earlier models that postulated differing mobility of these complexes. These novel findings thus hold significance for our understanding of photosynthesis regulation, particularly during state transitions.

• Klíčová slova
• Airyscan, FRAP, cyanobacteria, microdomain, photosystem, protein mobility, super-resolution microscopy, thylakoid membrane heterogeneity,
• Publikační typ
• časopisecké články MeSH

Thylakoid membranes are energy-converting membranes with a unique lipid composition. Though the membranes are primarily composed of proteins, their photosynthetic function is strongly influenced by the lipid constituents. Here we characterize, with molecular dynamics (MD) simulations, lipid bilayers with compositions representative of plant thylakoid membranes. We determine, in a wide range of temperatures, the physical parameters of the model membranes which are relevant for the photosynthetic function. We found a marked impact of temperature on membrane permeability due to a combination of increased compressibility and curvature of the membrane at elevated temperatures. With increasing temperatures, we observed increasingly smeared transmembrane density profiles of the membrane forming lipid headgroups predicting increased membrane flexibility. The diffusion coefficient of the lipids increased with temperature without apparent specificity for lipid species. Instead of a comprehensive experimental dataset in the relevant temperature range, we quantitatively compared and validated our MD results with MD simulations on a dipalmitoylphosphatidylcholine model system.

• Klíčová slova
• mechanical properties, molecular dynamics, permeability, thylakoid,
• Publikační typ
• časopisecké články MeSH

The present review is an attempt to conceptualize a contemporary understanding about the roles that cardiolipin, a mitochondrial specific conical phospholipid, and non-bilayer structures, predominantly found in the inner mitochondrial membrane (IMM), play in mitochondrial bioenergetics. This review outlines the link between changes in mitochondrial cardiolipin concentration and changes in mitochondrial bioenergetics, including changes in the IMM curvature and surface area, cristae density and architecture, efficiency of electron transport chain (ETC), interaction of ETC proteins, oligomerization of respiratory complexes, and mitochondrial ATP production. A relationship between cardiolipin decline in IMM and mitochondrial dysfunction leading to various diseases, including cardiovascular diseases, is thoroughly presented. Particular attention is paid to the targeting of cardiolipin by Szeto-Schiller tetrapeptides, which leads to rejuvenation of important mitochondrial activities in dysfunctional and aging mitochondria. The role of cardiolipin in triggering non-bilayer structures and the functional roles of non-bilayer structures in energy-converting membranes are reviewed. The latest studies on non-bilayer structures induced by cobra venom peptides are examined in model and mitochondrial membranes, including studies on how non-bilayer structures modulate mitochondrial activities. A mechanism by which non-bilayer compartments are formed in the apex of cristae and by which non-bilayer compartments facilitate ATP synthase dimerization and ATP production is also presented.

• Klíčová slova
• ATP synthase, cardiolipin, cardiovascular disease, electron-transport chain, inner mitochondrial membrane, non-bilayer structures,
• MeSH
• energetický metabolismus * MeSH
• kardiolipiny chemie   metabolismus   MeSH
• kardiovaskulární nemoci metabolismus   MeSH
• lidé MeSH
• lipidové dvojvrstvy metabolismus   MeSH
• mitochondriální membrány metabolismus   MeSH
• mitochondrie metabolismus   patologie   ultrastruktura   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• kardiolipiny MeSH
• lipidové dvojvrstvy MeSH

Biological membranes were originally described as a fluid mosaic with uniform distribution of proteins and lipids. Later, heterogeneous membrane areas were found in many membrane systems including cyanobacterial thylakoids. In fact, cyanobacterial pigment-protein complexes (photosystems, phycobilisomes) form a heterogeneous mosaic of thylakoid membrane microdomains (MDs) restricting protein mobility. The trafficking of membrane proteins is one of the key factors for long-term survival under stress conditions, for instance during exposure to photoinhibitory light conditions. However, the mobility of unbound 'free' proteins in thylakoid membrane is poorly characterized. In this work, we assessed the maximal diffusional ability of a small, unbound thylakoid membrane protein by semi-single molecule FCS (fluorescence correlation spectroscopy) method in the cyanobacterium Synechocystis sp. PCC6803. We utilized a GFP-tagged variant of the cytochrome b6f subunit PetC1 (PetC1-GFP), which was not assembled in the b6f complex due to the presence of the tag. Subsequent FCS measurements have identified a very fast diffusion of the PetC1-GFP protein in the thylakoid membrane (D = 0.14 - 2.95 µm2s-1). This means that the mobility of PetC1-GFP was comparable with that of free lipids and was 50-500 times higher in comparison to the mobility of proteins (e.g., IsiA, LHCII-light-harvesting complexes of PSII) naturally associated with larger thylakoid membrane complexes like photosystems. Our results thus demonstrate the ability of free thylakoid-membrane proteins to move very fast, revealing the crucial role of protein-protein interactions in the mobility restrictions for large thylakoid protein complexes.

• Klíčová slova
• FCS, cyanobacteria, photosynthesis, proteins mobility, thylakoids,
• Publikační typ
• časopisecké články MeSH