Sec14p

Sec14p is a cytosolic phosphatidylinositol transfer protein of the budding yeast Saccharomyces cerevisiae. It is essential for secretory traffic and proper function of the Golgi apparatus in yeast cells.

Biochemical function: Sec14p binds and transfers phospholipids, notably phosphatidylinositol (PI) and phosphatidylcholine (PC), between membranes. It operates through a lipid-exchange cycle in which it carries PC to the Golgi, releases PC, and binds PI. By regulating the availability of PI at the Golgi, Sec14p promotes the production of phosphatidylinositol 4-phosphate (PI4P) by the PI 4-kinase Pik1, coordinating lipid metabolism with Golgi trafficking processes.

Role in Golgi trafficking: The Sec14p cycle adjusts the lipid environment of Golgi membranes to favor vesicle budding and cargo sorting, linking lipid transfer to COPII vesicle formation and trafficking from the Golgi to the plasma membrane. The mechanism has been described as a lipid-exchange cycle that couples phospholipid transfer with signaling lipids.

Genetic and cellular phenotypes: SEC14 is essential; loss-of-function or temperature-sensitive sec14 mutants show severe defects in secretion, cargo mislocalization, and accumulation of secretory vesicles at the Golgi. Classical alleles include sec14-1 and related temperature-sensitive variants.

Family and evolution: Sec14p belongs to the Sec14-like phosphatidylinositol transfer protein family, with members found across eukaryotes. In yeast, Sec14p defines a key pathway regulating Golgi identity and trafficking. Structural studies reveal a Sec14-like lipid-binding domain that forms a hydrophobic pocket for PI and PC binding.