In this perspective we summarize current knowledge of the effect of monosialoganglioside GM1 on the membrane-mediated aggregation of the β-amyloid (Aβ) peptide. GM1 has been suggested to be actively involved in the development of Alzheimer's disease due to its ability to seed the aggregation of Aβ. However, GM1 is known to be neuroprotective against Aβ-induced toxicity. Here we suggest that the two scenarios are not mutually exclusive but rather complementary, and might depend on the organization of GM1 in membranes. Improving our understanding of the molecular details behind the role of gangliosides in neurodegenerative amyloidoses might help in developing disease-modifying treatments.
- MeSH
- amyloidní beta-protein chemie metabolismus MeSH
- G(M1) gangliosid chemie metabolismus MeSH
- lidé MeSH
- mozek metabolismus MeSH
- patologická konformace proteinů metabolismus MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
Extracellular and cytosolic leaflets in cellular membranes are distinctly different in lipid composition, yet they contribute together to signaling across the membranes. Here we consider a mechanism based on long-chain gangliosides for coupling the extracellular and cytosolic membrane leaflets together. Based on atomistic molecular dynamics simulations, we find that long-chain GM1 in the extracellular leaflet exhibits a strong tendency to protrude into the opposing bilayer leaflet. This interdigitation modulates the order in the cytosolic monolayer and thereby strengthens the interaction and coupling across a membrane. Coarse-grained simulations probing longer time scales in large membrane systems indicate that GM1 in the extracellular leaflet modulates the phase behavior in the cytosolic monolayer. While short-chain GM1 maintains phase-symmetric bilayers with a strong membrane registration effect, the situation is altered with long-chain GM1. Here, the significant interdigitation induced by long-chain GM1 modulates the behavior in the cytosolic GM1-free leaflet, weakening and slowing down the membrane registration process. The observed physical interaction mechanism provides a possible means to mediate or foster transmembrane communication associated with signal transduction.
Gangliosides located at the outer leaflet of plasma membrane are molecules that either participate in recognizing of exogenous ligand molecules or exhibit their own receptor activity, which are both essential phenomena for cell communication and signaling as well as for virus and toxin entry. Regulatory mechanisms of lipid-mediated recognition are primarily subjected to the physical status of the membrane in close vicinity of the receptor. Concerning the multivalent receptor activity of the ganglioside GM1, several regulatory strategies dealing with GM1 clustering and cholesterol involvement have been proposed. So far however, merely the isolated issues were addressed and no interplay between them investigated. In this work, several advanced fluorescence techniques such as Z-scan fluorescence correlation spectroscopy, Förster resonance energy transfer combined with Monte Carlo simulations, and a newly developed fluorescence antibunching assay were employed to give a more complex portrait of clustering and cholesterol involvement in multivalent ligand recognition of GM1. Our results indicate that membrane properties have an impact on a fraction of GM1 molecules that is not available for the ligand binding. While at low GM1 densities (~1 %) it is the cholesterol that turns GM1 headgroups invisible, at higher GM1 level (~4 %) it is purely the local density of GM1 molecules that inhibits the recognition. At medium GM1 content, cooperation of the two phenomena occurs. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.
- MeSH
- buněčná membrána metabolismus MeSH
- cholesterol MeSH
- difuze MeSH
- G(M1) gangliosid chemie metabolismus MeSH
- hydraziny metabolismus MeSH
- ligandy MeSH
- metoda Monte Carlo MeSH
- ovce MeSH
- počítačová simulace MeSH
- receptory buněčného povrchu metabolismus MeSH
- rezonanční přenos fluorescenční energie MeSH
- shluková analýza MeSH
- titrace MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Changes of membrane organization upon cross-linking of its components trigger cell signaling response to various exogenous factors. Cross-linking of raft gangliosides GM1 with cholera toxin (CTxB) was shown to cause microscopic phase separation in model membranes, and the CTxB-GM1 complexes forming a minimal lipid raft unit are the subject of ongoing cell membrane research. Yet, those subdiffraction sized rafts have never been described in terms of size and dynamics. By means of two-color z-scan fluorescence correlation spectroscopy, we show that the nanosized domains are formed in model membranes at lower sphingomyelin (Sph) content than needed for the large-scale phase separation and that the CTxB-GM1 complexes are confined in the domains poorly stabilized with Sph. Förster resonance energy transfer together with Monte Carlo modeling of the donor decay response reveal the domain radius of ~8 nm, which increases at higher Sph content. We observed two types of domains behaving differently, which suggests a dual role of the cross-linker: first, local transient condensation of the GM1 molecules compensating for a lack of Sph and second, coalescence of existing nanodomains ending in large-scale phase separation.
- MeSH
- chemické modely MeSH
- cholerový toxin chemie MeSH
- fluidita membrány MeSH
- G(M1) gangliosid chemie MeSH
- lipidové dvojvrstvy chemie MeSH
- membránové mikrodomény chemie ultrastruktura MeSH
- molekulární konformace MeSH
- molekulární modely MeSH
- reagencia zkříženě vázaná chemie MeSH
- změna skupenství MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
A comparison of histochemical detection of GM1 ganglioside in cryostat sections using cholera toxin B-subunit after fixation with 4% formaldehyde and dry acetone gave tissue-dependent results. In the liver no pre-treatment showed detectable differences related to GM1 reaction products, while studies in the brain showed the superiority of acetone pre-extraction (followed by formaldehyde), which yielded sharper images compared with the diffuse, blurred staining pattern associated with formaldehyde. Therefore, the aim of our study was to define the optimal conditions for the GM1 detection using cholera toxin B-subunit. Ganglioside extractability with acetone, the ever neglected topic, was tested comparing anhydrous acetone with acetone containing admixture of water. TLC analysis of acetone extractable GM1 ganglioside from liver sections did not exceed 2% of the total GM1 ganglioside content using anhydrous acetone at -20 degrees C, and 4% at room temperature. The loss increased to 30.5% using 9:1 acetone/water. Similarly, photometric analysis of lipid sialic acid, extracted from dried liver homogenates with anhydrous acetone, showed the loss of gangliosides into acetone 3.0 +/- 0.3% only. The loss from dried brain homogenate was 9.5 +/- 1.1%. Thus, anhydrous conditions (dry tissue samples and anhydrous acetone) are crucial factors for optimal in situ ganglioside detection using acetone pre-treatment. This ensures effective physical fixation, especially in tissues rich in polar lipids (precipitation, prevention of in situ diffusion), and removal of cholesterol, which can act as a hydrophobic blocking barrier.
- MeSH
- aceton chemie MeSH
- cholerový toxin chemie MeSH
- cholesterol analýza MeSH
- G(M1) gangliosid analýza chemie MeSH
- imunohistochemie MeSH
- játra chemie cytologie MeSH
- krysa rodu rattus MeSH
- mozek cytologie MeSH
- potkani Wistar MeSH
- zvířata MeSH
- Check Tag
- krysa rodu rattus MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
