Ca2+-regulated exocytosis and SNARE function

Secretory vesicles formed at the trans-Golgi network of neuroendocrine and endocrine cells must undergo several steps, such as translocation, docking and priming, before they are ready to fuse with the plasma membrane and deliver their cargo into the extracellular space. This process is called regulated exocytosis and is controlled by Ca2+ (using synaptotagmin) and mediated by SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) proteins. Recent studies from three leading laboratories reveal novel details about the mechanism by which Ca2+ and SNAREs regulate this complex process. These findings highlight the roles of both SNAP25 (synaptosome-associated protein of 25kD), one of the SNARE proteins, and CAPS (Ca2+-dependent activator protein for secretion), a Ca2+-sensor protein, in vesicle priming, depriming and fusion.