Annexins in the secretory pathway.

Among the multiplicity of roles suggested for proteins of the annexin family, those implicating these proteins in regulated exocytosis remain among the most convincing. Studies in this area of annexin biology have focused on annexin II, which because of its unusually low Ca(2+)-requirement for phospholipid-binding has many of the requisite properties of a membrane fusogenic Ca2+ sensor. Other annexins are also good candidates for exocytotic mediators, especially annexins I and VII, which have strong vesicle-aggregating activities. In contrast, annexin VI appears to block vesicle aggregation, perhaps acting as a negative regulator of exocytosis. In this review, we consider the evidence for and against annexins having functions in the secretory pathway.