Phosphatidylserine

Phosphatidylserine is an anionic glycerophospholipid found mainly in the inner leaflet of animal-cell plasma membranes. Its headgroup participates in membrane organization and signaling, and its appearance on the outer surface can mark cells for clearance.

Phospholipid bilayer: A membrane structure formed by two layers of phospholipids, with hydrophilic headgroups facing water and hydrophobic tails inward. Phosphatidylserine is one lipid species within this membrane-forming structure.
Apoptosis: A regulated form of cell death involving characteristic biochemical and structural changes. Apoptotic cells commonly expose phosphatidylserine as an engulfment cue.
Glycerophospholipid: A membrane lipid built from a glycerol backbone, two fatty-acid chains, and a phosphate-containing headgroup. Phosphatidylserine is a specific glycerophospholipid with serine in its headgroup.
Blood coagulation cascade: A sequence of reactions that generates thrombin and forms a fibrin clot. Phosphatidylserine-rich platelet surfaces provide a platform for key cascade reactions.
Lipid asymmetry: The unequal distribution of different lipid species between the two leaflets of a biological membrane. Phosphatidylserine is concentrated on the cytoplasmic leaflet, creating a signal-bearing asymmetry.
Annexin V assay: A laboratory method that detects cell-surface phosphatidylserine using fluorescently labeled annexin V. This assay uses phosphatidylserine exposure to identify cells undergoing apoptosis.
Serine: A polar amino acid whose side chain contains a hydroxyl group. Serine supplies the headgroup attached to phosphate in phosphatidylserine.
Phagocytosis: The cellular engulfment of particles, microbes, or other cells into internal compartments. Phosphatidylserine exposure promotes phagocytic removal of dying cells.
Flippase: A membrane transport protein that moves selected lipids from one leaflet of a bilayer to the other using energy. Flippases help maintain phosphatidylserine on the inner membrane leaflet.
Coagulation: The process by which blood forms a clot through coordinated activation of plasma proteins and platelets. Exposed phosphatidylserine on activated platelets supports assembly of coagulation enzyme complexes.

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