cytosolicmembrane

Cytosolic membrane is not a standard formal term in cell biology, but is sometimes used informally to refer to the portion of a biological membrane that faces the cytosol, or to the cytosolic (inner) leaflet of a phospholipid bilayer. In most contexts, scientists distinguish between the two leaflets of a membrane: the cytosolic leaf­let facing the cytosol, and the exoplasmic leaf­let facing the extracellular space or organelle lumen.

Membranes are composed of a lipid bilayer with embedded and associated proteins. The cytosolic leaflet often has a distinct lipid composition from the outer leaflet, with higher concentrations of certain negatively charged lipids such as phosphatidylserine and phosphatidylinositol phosphates in many cells. This lipid asymmetry helps recruit cytosolic proteins that contain lipid-binding domains, support signaling cascades, and anchor cytoskeletal elements to the membrane.

Functions associated with the cytosolic membrane include mediating signal transduction, organizing protein complexes at the membrane surface, and driving membrane curvature and vesicle trafficking. Proteins on the cytosolic side can include kinases, adaptor proteins, small GTPases, and cytoskeletal linkers. Enzymes located at or near the cytosolic leaf­let participate in processes such as phosphoinositide metabolism and endocytosis.

Maintenance of asymmetry between leaflets is actively regulated by enzymes such as flippases, floppases, and scramblases. The term cytosolic membrane is often replaced in precise writing by references to the cytosolic (inner) leaflet or to the plasma membrane’s cytosolic face, depending on context.