Rat Annexin V Crystal Structure: Ca ²⁺ -Induced Conformational Changes

Annexins are a family of calcium- and phospholipid-binding proteins implicated in mediating membrane-related processes such as secretion, signal transduction, and ion channel activity. The crystal structure of rat annexin V was solved to 1.9 angstrom resolution by multiple isomorphous replacement. Unlike previously solved annexin V structures, all four domains bound calcium in this structure. Calcium binding in the third domain induced a large relocation of the calcium-binding loop regions, exposing the single tryptophan residue to the solvent. These alterations in annexin V suggest a role for domain 3 in calcium-triggered interaction with phospholipid membranes.