Sec15

Sec15 is a protein subunit of the exocyst complex, a conserved multi-protein tethering complex that mediates the targeting and initial tethering of secretory vesicles to the plasma membrane during exocytosis. It plays a key role in enabling polarized secretion by helping vesicles dock at specific sites on the cell surface before membrane fusion.

In most organisms, Sec15 is one component of the eight-subunit exocyst, alongside Sec3, Sec5, Sec6, Sec8, Sec10, Exo70, and Exo84. In yeast, Sec15 is known to interact with Rab GTPases on the vesicle, particularly Sec4-GTP, and to coordinate with other exocyst subunits to assemble a tethering complex at sites of active secretion. In higher eukaryotes, Sec15 is part of a similar exocyst complex, with vertebrate paralogs allowing tissue- or context-specific functions.

Functionally, Sec15 localizes to regions of the plasma membrane where secretion occurs and facilitates the initial capture and tethering of secretory vesicles, a step that precedes SNARE-mediated fusion. Its activity is connected to the proper organization of cell polarity and directed exocytosis, processes essential for growth, differentiation, and specialized cellular functions such as neuronal outgrowth and epithelial secretion.

Regulation of Sec15 and the exocyst involves small GTPases and phosphoinositide signaling that govern vesicle trafficking and exocyst assembly. Disruption of Sec15 or other exocyst components can impair secretion, affect cell polarity, and influence developmental and physiological processes across eukaryotes.