Role of VPS33B in α-granule formation. Proteins are delivered to MVB I through the trans-Golgi network via the synthetic pathway and through the plasma membrane via the endocytotic pathway. VPS33B in complex with VIPAR (VPS16B) mediates maturation of α-granules during the transition from MVB I to MVB II, and potentially during the delivery of cargos directly from the Golgi to MVB II. VPS33A and VSP16A function in dense granule maturation. The figure is adapted from Figure 7C in the article by Bem et al that begins on page 133, by professional illustrator Patrick Lane, ScEYEnce Studios.