The annexins are a family of calcium-dependent phospholipid-binding proteins. Members of the annexin family contain 4 internal repeat domains, each of which includes a type II calcium-binding site. The calcium-binding sites are required for annexins to aggregate and cooperatively bind anionic phospholipids and extracellular matrix proteins. The most striking feature of annexin 31 is a complete ablation of all four homologous type II calcium-binding sites in the conserved tetrad core. Although all 4 type II calcium-binding sites in annexin 31 contained AA substitutions that ablated their function, structural analysis suggests that the conserved putative ion channel formed by the tetrad core is intact Synonyms: Annexin A9, Annexin-9, Annexin-31, Annexin XXXI, Pemphaxin, ANXA9, ANX31