V-type proton ATPase subunit S1 (ATP6AP1)

Accessory subunit of the proton-transporting vacuolar (V)-ATPase protein pump, which is needed for luminal acidification of secretory vesicles. Guides the V-type ATPase into specialized subcellular compartments, such as neuroendocrine regulated secretory vesicles or the ruffled border of the osteoclast, thereby regulating its activity.

Involved in membrane trafficking and Ca(2+)-dependent membrane fusion. May play a role in the assembly of the V-type ATPase complex.