Annexin VI is an eight repeat member of the annexin family of proteins which are both water soluble and bind to negatively charged phospholipids in a calcium-dependent manner. Here we present a model for annexin VI based on fitting the three-dimensional structure of two annexin V molecules (Huber (1990) EMBO J. 9, 3867–23;874) to the two-dimensional stain-excluding density of lipid-bound annexin VI (Newman (1989) J. Mol. Biol. 206, 213–219). Both annexin VI lobes could only be fitted with their convex faces closest to the lipid monolayer. This supports the hypothesis that annexin—lipid binding is mediated by the interaction between calcium bound to the loops protruding from the convex protein surface and phospholipid headgroups.
