PSS1

PSS1, or phosphatidylserine synthase 1, is an enzyme that synthesizes phosphatidylserine (PS), a major anionic phospholipid, in eukaryotic cells. It is encoded by the PSS1 gene in humans and other mammals, and is often coexpressed with a second PS synthase, PSS2, to provide PS through distinct base-exchange reactions.

PSS1 catalyzes the base-exchange reaction in which serine substitutes for the headgroup of phosphatidylcholine (PC) to yield PS and choline. PSS2 performs a similar reaction with phosphatidylethanolamine (PE) to give PS and ethanolamine.

PSS1 is a membrane-associated enzyme located in the endoplasmic reticulum, with multiple transmembrane segments in many species.

PS produced by PSS1 contributes to membrane lipid composition, especially inner-leaflet PS, and provides substrate for further lipid remodeling. PS participates in signaling pathways, coagulation, and apoptosis when externalized.

Expression and activity are influenced by cellular lipid demand, substrate availability (PC and serine), and possibly signaling pathways. PSS1 is conserved across eukaryotes; in yeast a related enzyme is CHO1.

Abnormal PS synthesis can affect membrane properties and cell signaling; studies of PSS1 help understand lipid homeostasis and metabolic diseases.