Sec3

Sec3 is a component of the exocyst, a conserved eight-subunit protein complex that tethers secretory vesicles to the plasma membrane in eukaryotic cells. It plays a central role in exocytosis by helping define sites of vesicle docking and facilitating SNARE-mediated fusion.

In budding yeast (Saccharomyces cerevisiae), Sec3 is one of the exocyst subunits and is distinctive for its direct association with the plasma membrane. Its N-terminal region can bind phospholipids, particularly phosphatidylinositol 4,5-bisphosphate (PIP2), and interact with small GTPases such as Cdc42 and Rho-family proteins. This membrane-targeting function helps establish and maintain polarity for directed secretion.

The exocyst complex comprises Sec3, Sec5, Sec6, Sec8, Sec10, Sec12, Exo70, and Exo84 (the exact naming can vary by species). Sec3’s membrane-anchoring role contrasts with other subunits that assemble primarily at the vesicle or docking site, making Sec3 an important landmark for exocytosis.

Across eukaryotes, Sec3 has conserved homologs, with vertebrates possessing a counterpart known as EXOC3. While the exact regulatory details differ among organisms, the overall function—tethering secretory vesicles to specific plasma membrane sites to enable polarized secretion—remains a common theme.

Disruption of Sec3 or other exocyst components impairs exocytosis and affects polarized growth and development, reflecting the exocyst’s essential role in membrane trafficking and cell polarity.