Molecular mechanism of docking of dense-core vesicles to the plasma membrane in neuroendocrine cells.

Almost every cell in our organism releases proteins and other biological substances using a fundamental cellular process known as constitutive exocytosis. In contrast, in exocrine and endocrine glands, the cells are inherent in an additional and more refined release mechanism directly tuned by extracellular signals. This process, referred to as regulated exocytosis, ensures the timely delivery of molecules such as peptide hormones and digestive enzymes to the exact moment-to-moment requirements of the organism. Recent studies of the final step of hormone secretion have been shown that the monomeric GTPase Rab27 subfamily and its cell type-or tissue-specific Rab27-binding protein(s) [also called Rab27 effector(s)] exist on the hormone-containing dense-core vesicle membrane and regulate the secretion of peptide hormones in endocrine cells. Synaptotagmin-like proteins (Slps) and rabphilin contain an N-terminal Rab27-binding domain and C-terminal tandem C2 domains, and some of the Rab27-binding proteins have recently been shown to promote docking of dense-core vesicles to the plasma membrane in a variety of secretory cells. We discuss here the evidence supporting a molecular mechanism for the way that the Rab27 and Rab27 effector complex controls the docking step in the trafficking of dense-core vesicles in neuroendocrine cells.