Ride the wave: Retrograde trafficking becomes Ca2+ dependent with BAI AP3

Abstract

The functions of four of the five proteins in the mammalian uncoordinated-13 (Munc13) family have been identified as priming factors in SNA RE-dependent exocytosis. In this issue, Zhang et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201702099) show that the fifth member, BAI AP3 (brain-specific angiogenesis inhibitor I-associated protein 3), acts in retrograde trafficking by returning secretory vesicle material to the trans-Golgi network. In its absence, secretory vesicle formation is impaired, leading to accumulation of immature vesicles, or lysosomal vesicle degradation.