membrane raft

Definition

Target type: cellularcomponent

Any of the small (10-200 nm), heterogeneous, highly dynamic, sterol- and sphingolipid-enriched membrane domains that compartmentalize cellular processes. Small rafts can sometimes be stabilized to form larger platforms through protein-protein and protein-lipid interactions. [PMID:16645198, PMID:20044567]

Membrane rafts are specialized microdomains within the plasma membrane that are enriched in specific lipids and proteins. They are characterized by their high concentration of cholesterol, sphingolipids, and glycosylphosphatidylinositol (GPI)-anchored proteins. These components contribute to the formation of a more ordered and tightly packed lipid bilayer, distinct from the surrounding membrane.

Membrane rafts are dynamic structures that can assemble and disassemble in response to cellular signals. They play crucial roles in various cellular processes, including signal transduction, cell adhesion, and endocytosis.

**Lipid Composition:**

- **Cholesterol:** A sterol that intercalates between phospholipid molecules, increasing membrane rigidity and reducing fluidity.
- **Sphingolipids:** A class of lipids with a sphingosine backbone, including sphingomyelin and glycosphingolipids. They contribute to the formation of thicker and more ordered lipid bilayers.
- **Glycosylphosphatidylinositol (GPI)-anchored proteins:** Proteins anchored to the outer leaflet of the plasma membrane via a GPI anchor. These proteins are often enriched in membrane rafts and play roles in signaling and cell-cell interactions.

**Protein Composition:**

- **Signaling proteins:** Membrane rafts are enriched in signaling proteins involved in various pathways, such as growth factor signaling, immune responses, and neuronal signaling.
- **Adhesion molecules:** Cell adhesion molecules, such as integrins and cadherins, are often associated with membrane rafts, contributing to cell-cell and cell-matrix interactions.
- **Lipid-modifying enzymes:** Enzymes involved in lipid metabolism, such as lipid kinases and phosphatases, are also localized to membrane rafts, regulating lipid composition and signaling.

**Structural Features:**

- **Ordered lipid bilayer:** The high concentration of cholesterol and sphingolipids creates a more ordered and tightly packed lipid bilayer, distinct from the surrounding membrane.
- **Lateral heterogeneity:** Membrane rafts exist as small, dynamic domains that can laterally segregate within the plasma membrane.
- **Association with cytoskeleton:** Membrane rafts can interact with the underlying cytoskeleton, providing structural support and influencing their dynamics.

**Functions:**

- **Signal transduction:** Membrane rafts serve as platforms for the assembly and activation of signaling complexes, facilitating signal transduction pathways.
- **Cell adhesion:** Membrane rafts play roles in cell-cell and cell-matrix adhesion through the localization of adhesion molecules.
- **Endocytosis:** Membrane rafts mediate the uptake of molecules through clathrin-independent endocytosis, a process that involves the formation of small vesicles.
- **Viral entry and pathogenesis:** Some viruses utilize membrane rafts as entry points into cells, highlighting their importance in infectious diseases.

Membrane rafts are complex and dynamic structures that play crucial roles in cellular function. Understanding their composition and functions is essential for comprehending various cellular processes and disease mechanisms.'
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Proteins (80)

Compounds (2,303)