Annexin A2 (ANXA2), is an ~40kD member of the Annexin family of calcium-dependent phospholipid-binding proteins that are preferentially located on the cytosolic face of the plasma membrane. Phosphorylation of Annexin A2 at Tyr23 regulates its involvement in endosomal trafficking and actin cytoskeleton rearrangement. The Annexins consist of a unique amino terminal domain followed by a homologous C-terminal core domain containing the calcium-dependent phospholipid-binding sites. The C-terminal domain is comprised of four 60-70aa annexin repeats. Annexin A2 also functions as an autocrine factor to enhance osteoclast formation and bone resorption and is a major cellular substrate of the tyrosine kinase Src. Human Annexin A2 shares 97% identity with mouse and rat Annexin A2.