Selective sorting of alpha‐granule proteins

One of the main functions of blood platelets is to secrete a variety of substances that can modify a developing thrombus, regulate the growth of the vasculature, promote wound repair, and contribute to cell‐adhesive events. A majority of this vast array of secreted proteins are stored in alpha‐granules. Until recently, it was assumed that platelets contained one homogeneous population of alpha‐granules that undergo complete de‐granulation during platelet activation. This review focuses on the mechanisms of alpha‐granule biogenesis and secretion, with a particular emphasis on recent findings that clearly demonstrate that platelets contain distinct subpopulations of alpha‐granules that undergo differential release during activation. We consider the implications of this new paradigm of platelet secretion, discuss mechanisms of alpha‐granule biogenesis, and review the molecular basis of transport and delivery of alpha‐granules to assembling platelets.