Membrane microdomains denoted commonly as lipid rafts (or membrane rafts) have been implicated in T-cell receptor (TCR), and more generally immunoreceptor, signaling for over 25 years. However, this area of research has been complicated by doubts about the real nature (and even existence) of these membrane entities, especially because of methodological problems connected with possible detergent artefacts. Recent progress in biophysical approaches and functional studies of raft resident proteins apparently clarified many controversial aspects in this area. At present, the prevailing view is that these membrane microdomains are indeed involved in many aspects of cell biology, including immunoreceptor signaling. Moreover, several other types of raft-like microdomains (perhaps better termed nanodomains) have been described, which apparently also play important biological roles.
- MeSH
- Humans MeSH
- Membrane Microdomains chemistry metabolism MeSH
- Receptors, Antigen, T-Cell metabolism MeSH
- Signal Transduction * MeSH
- Animals MeSH
- Check Tag
- Humans MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Review MeSH
Lateral segregation of plasma membrane lipids is a generally accepted phenomenon. Lateral lipid microdomains of specific composition, structure and biological functions are established as a result of simultaneous action of several competing mechanisms which contribute to membrane organization. Various lines of evidence support the conclusion that among those mechanisms, the membrane potential plays significant and to some extent unique role. Above all, clear differences in the microdomain structure as revealed by fluorescence microscopy could be recognized between polarized and depolarized membranes. In addition, recent fluorescence spectroscopy experiments reported depolarization-induced changes in a membrane lipid order. In the context of earlier findings showing that plasma membranes of depolarized cells are less susceptible to detergents and the cells less sensitive to antibiotics or antimycotics treatment we discuss a model, in which membrane potential-driven re-organization of the microdomain structure contributes to maintaining membrane integrity during response to stress, pathogen attack and other challenges involving partial depolarization of the plasma membrane. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.
- MeSH
- Cell Membrane metabolism physiology MeSH
- Humans MeSH
- Membrane Microdomains chemistry metabolism physiology MeSH
- Membrane Potentials physiology MeSH
- Lipid Metabolism physiology MeSH
- Animals MeSH
- Check Tag
- Humans MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Review MeSH
The existence of specialized microdomains in plasma membranes, postulated for almost 25 years, has been popularized by the concept of lipid or membrane rafts. The idea that detergent-resistant membranes are equivalent to lipid rafts, which was generally abandoned after a decade of vigorous data accumulation, contributed to intense discussions about the validity of the raft concept. The existence of membrane microdomains, meanwhile, has been verified by unequivocal independent evidence. This review summarizes the current state of research in plants and fungi with respect to common aspects of both kingdoms. In these organisms, principally immobile microdomains large enough for microscopic detection have been visualized. These microdomains are found in the context of cell-cell interactions (plant symbionts and pathogens), membrane transport, stress, and polarized growth, and the data corroborate at least three mechanisms of formation. As documented in this review, modern methods of visualization of lateral membrane compartments are also able to uncover the functional relevance of membrane microdomains.
- MeSH
- Biological Transport MeSH
- Cell Membrane chemistry metabolism MeSH
- Detergents MeSH
- Fungi chemistry metabolism MeSH
- Membrane Microdomains chemistry metabolism MeSH
- Plant Cells chemistry metabolism MeSH
- Plants chemistry metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Review MeSH
Membrane rafts and signaling molecules associated with them are thought to play important roles in immunoreceptor signaling. Rafts differ in their lipid and protein compositions from the rest of the membrane and are relatively resistant to solubilization by Triton X-100 or similar detergents, producing buoyant, detergent-resistant membranes (DRMs) that can be isolated by density gradient ultracentrifugation. One of the key signaling molecules present in T cell DRMs is the transmembrane adaptor protein LAT (linker for activation of T cells). In contrast to previous results, a recent study demonstrated that a LAT construct not present in the buoyant DRMs is fully able to support TCR signaling and development of T cells in vivo. This finding caused doubts about the real physiological role of rafts in TCR signaling. In this study, we demonstrate that these results can be explained by the existence of a novel type of membrane raft-like microdomains, producing upon detergent solubilization "heavy DRMs" containing a number of membrane molecules. At a moderate level of expression, LAT supported TCR signaling more efficiently than constructs targeted to the microdomains producing heavy DRMs or to nonraft membrane. We suggest that different types of membrane microdomains provide environments regulating the functional efficiencies of signaling molecules present therein.
- MeSH
- Adaptor Proteins, Signal Transducing immunology metabolism MeSH
- Lymphocyte Activation immunology MeSH
- Jurkat Cells MeSH
- Humans MeSH
- Membrane Microdomains chemistry immunology MeSH
- Membrane Proteins chemistry immunology isolation & purification metabolism MeSH
- Receptors, Antigen, T-Cell immunology metabolism MeSH
- Signal Transduction immunology MeSH
- T-Lymphocytes chemistry immunology metabolism MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
The organization of biological membranes into structurally and functionally distinct lateral microdomains is generally accepted. From bacteria to mammals, laterally compartmentalized membranes seem to be a vital attribute of life. The crucial fraction of our current knowledge about the membrane microdomains has been gained from studies on fungi. In this review we summarize the evidence of the microdomain organization of membranes from fungal cells, with accent on their enormous diversity in composition, temporal dynamics, modes of formation, and recognized engagement in the cell physiology. A special emphasis is laid on the fact that in addition to their other biological functions, membrane microdomains also mediate the communication among different membranes within a eukaryotic cell and coordinate their functions. Involvement of fungal membrane microdomains in stress sensing, regulation of lipid homeostasis, and cell differentiation is discussed more in detail.
Eisosomes are plasma membrane-associated protein complexes organizing the membrane compartment of Can1 (MCC), a membrane microdomain of specific structure and function in ascomycetous fungi. By heterologous expression of specific components of Schizosaccharomyces pombe eisosomes in Saccharomyces cerevisiae we reconstitute structures exhibiting the composition and morphology of S. pombe eisosome in the host plasma membrane. We show S. pombe protein Pil1 (SpPil1) to substitute the function of its S. cerevisiae homologue in building plasma membrane-associated assemblies recognized by inherent MCC/eisosome constituents Sur7 and Seg1. Our data indicate that binding of SpPil1 to the plasma membrane of S. cerevisiae also induces formation of furrow-like invaginations characteristic for MCC. To the best of our knowledge, this is the first report of interspecies transfer of a functional plasma membrane microdomain. In the described system, we identify a striking difference between eisosome stabilizer proteins Seg1 and SpSle1. While Seg1 recruits both Pil1 and SpPil1 to the plasma membrane, SpSle1 recognizes only its natural counterpart, SpPil1. In the presence of Pil1, SpSle1 is segregated outside the Pil1-organized eisosomes and forms independent microdomains in the host membrane.
- MeSH
- Cell Membrane metabolism MeSH
- Cytoskeletal Proteins metabolism MeSH
- Phosphoproteins metabolism MeSH
- Membrane Microdomains metabolism MeSH
- Membrane Proteins metabolism MeSH
- Saccharomyces cerevisiae Proteins metabolism MeSH
- Saccharomyces cerevisiae metabolism MeSH
- Schizosaccharomyces pombe Proteins metabolism MeSH
- Schizosaccharomyces metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Thy-1 (CD90) is a glycoprotein bound to the plasma membrane by a GPI anchor. Aggregation of Thy-1 in mast cells and basophils induces activation events independent of the expression of Fcepsilon receptor I (FcepsilonRI). Although we and others have previously suggested that plasma membrane microdomains called lipid rafts are implicated in both Thy-1 and FcepsilonRI signaling, properties of these microdomains are still poorly understood. In this study we used rat basophilic leukemia cells and their transfectants expressing both endogenous Thy-1.1 and exogenous Thy-1.2 genes and analyzed topography of the Thy-1 isoforms and Thy-1-induced signaling events. Light microscopy showed that both Thy-1 isoforms were in the plasma membrane distributed randomly and independently. Electron microscopy on isolated membrane sheets and fluorescence resonance energy transfer analysis indicated cross-talk between Thy-1 isoforms and between Thy-1 and FcepsilonRI. This cross-talk was dependent on actin filaments. Thy-1 aggregates colocalized with two transmembrane adaptor proteins, non-T cell activation linker (NTAL) and linker for activation of T cells (LAT), which had been shown to inhabit different membrane microdomains. Thy-1 aggregation led to tyrosine phosphorylation of these two adaptors. The combined data indicate that aggregated GPI-anchored proteins can attract different membrane proteins in different clusters and thus can trigger different signaling pathways.
- MeSH
- Adaptor Proteins, Signal Transducing metabolism MeSH
- Actins metabolism MeSH
- Thy-1 Antigens genetics metabolism MeSH
- Financing, Organized MeSH
- Phosphoproteins metabolism MeSH
- Immunoblotting MeSH
- Microscopy, Immunoelectron MeSH
- Receptor Cross-Talk MeSH
- Rats MeSH
- Mast Cells immunology metabolism ultrastructure MeSH
- Membrane Microdomains ultrastructure MeSH
- Membrane Proteins metabolism MeSH
- Protein Isoforms genetics metabolism MeSH
- Receptors, IgE immunology metabolism MeSH
- Fluorescence Resonance Energy Transfer MeSH
- Signal Transduction immunology MeSH
- Transfection MeSH
- Animals MeSH
- Check Tag
- Rats MeSH
- Animals MeSH
Thylakoids are the place of the light-photosynthetic reactions. To gain maximal efficiency, these reactions are conditional to proper pigment-pigment and protein-protein interactions. In higher plants thylakoids, the interactions lead to a lateral asymmetry in localization of protein complexes (i.e. granal/stromal thylakoids) that have been defined as a domain-like structures characteristic by different biochemical composition and function (Albertsson P-Å. 2001,Trends Plant Science 6: 349-354). We explored this complex organization of thylakoid pigment-proteins at single cell level in the cyanobacterium Synechocystis sp. PCC 6803. Our 3D confocal images captured heterogeneous distribution of all main photosynthetic pigment-protein complexes (PPCs), Photosystem I (fluorescently tagged by YFP), Photosystem II and Phycobilisomes. The acquired images depicted cyanobacterial thylakoid membrane as a stable, mosaic-like structure formed by microdomains (MDs). These microcompartments are of sub-micrometer in sizes (~0.5-1.5 μm), typical by particular PPCs ratios and importantly without full segregation of observed complexes. The most prevailing MD is represented by MD with high Photosystem I content which allows also partial separation of Photosystems like in higher plants thylakoids. We assume that MDs stability (in minutes) provides optimal conditions for efficient excitation/electron transfer. The cyanobacterial MDs thus define thylakoid membrane organization as a system controlled by co-localization of three main PPCs leading to formation of thylakoid membrane mosaic. This organization might represent evolutional and functional precursor for the granal/stromal spatial heterogeneity in photosystems that is typical for higher plant thylakoids.
- MeSH
- Bacterial Proteins metabolism MeSH
- Photosynthesis physiology MeSH
- Photosystem I Protein Complex metabolism MeSH
- Photosystem II Protein Complex metabolism MeSH
- Phycobilisomes metabolism MeSH
- Microscopy, Confocal MeSH
- Membrane Microdomains metabolism MeSH
- Synechocystis MeSH
- Thylakoids metabolism MeSH
- Imaging, Three-Dimensional MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
An advantageous alternative to the use of detergents in biochemical studies on membrane proteins are the recently developed styrene-maleic acid (SMA) amphipathic copolymers. In our recent study [1] we demonstrated that using this approach, most T cell membrane proteins were fully solubilized (presumably in small nanodiscs), while two types of raft proteins, GPI-anchored proteins and Src family kinases, were mostly present in much larger (>250 nm) membrane fragments markedly enriched in typical raft lipids, cholesterol and lipids containing saturated fatty acid residues. In the present study we demonstrate that disintegration of membranes of several other cell types by means of SMA copolymer follows a similar pattern and we provide a detailed proteomic and lipidomic characterization of these SMA-resistant membrane fragments (SRMs).
