Crystal structure of the annexin XII hexamer and implications for bilayer insertion

The 2.8 angstrom resolution atomic structure of the annexin XII hexamer reveals a 210K homohexamer with 3-2 symmetry in the asymmetric unit. The 70-angstrom-thick hexamer forms a concave disk with a diameter of 100 angstroms. Six Ca2+ ions are present in the hexamer formation. A novel model for annexin-phospholipid bilayer interaction indicates that Ca2+ sites present on the perimeter of the hexamer regulate the hydrophilic insertion of the protein complex into the phospholipid layer.