lipidraft

Lipid raft, sometimes written as lipidraft, is a proposed subdomain of the cell membrane. It is characterized by a distinct lipid composition, notably enriched in cholesterol and sphingolipids, which forms regions that are more ordered and tightly packed than the surrounding phospholipid bilayer. Lipid rafts are thought to exist as small, dynamic platforms that can assemble and disperse in response to cellular conditions.

Composition and properties: Lipid rafts are enriched in saturated acyl chains and cholesterol, and host specific proteins including GPI-anchored proteins, certain receptor molecules, and signaling kinases such as members of the Src family. Their reported size ranges from roughly 10 to 200 nanometers, and their organization is often transient and reversible, influenced by temperature, lipid composition, and cytoskeletal interactions.

Functions: These microdomains are thought to organize signaling by concentrating receptor complexes and kinases, thereby modulating signal initiation and propagation. They play roles in immune cell activation, sensory signaling, and membrane trafficking. Lipid rafts have also been implicated in endocytosis, caveolar pathways, and in the entry processes of some pathogens.

Evidence and debates: The concept originated from observations of detergent-resistant membranes and co-fractionation studies, but such methods can introduce artifacts. Modern approaches, including advanced fluorescence microscopy and single-molecule tracking, suggest that lipid rafts are nanoscale, dynamic assemblies rather than static structures. The field now emphasizes transient, context-dependent nanodomains rather than fixed rafts.

History and terminology: The lipid raft concept was popularized in the 1990s by Simons and Ikonen. While still debated, the idea has influenced our understanding of membrane organization and signaling. In literature, the term lipid raft may appear as a single word, lipidraft, though most sources use two words.