Annexin V forms calcium-dependent trimeric units on phospholipid vesicles

The quaternary structure of annexin V, a calcium-dependent phospholipid binding protein, was investigated by chemical cross-linking. Calcium was found to induce the formation of trimers, hexamers, and higher aggregates only when anionic phospholipids were present. Oligomerization occurred under the same conditions as annexin—vesicle binding. A model is proposed in when cell stimulation leads to calcium-induced organization of arrays of annexin V lining the inner membrane surface, thus altering properties such as permeability and fluidity.