The EF-hand domain is a twelve amino acid loop motif that is commonly found in proteins that participate in calcium-binding events within the cell. EF-hand domains generally exist in a pair that, together, form a stable four-helix bundle that enables the binding of calcium ions. EF-HB (EF-hand domain-containing family member B) is a 831 amino acid protein that contains two EF-hand domains, suggesting a role in calcium-mediated events throughout the cell. There are three isoforms of EF-HB that are produced as a result of alternative splicing events. The gene encoding EF-HB is located on human chromosome three,which is made up of about 214 million bases encoding over 1,100 genes, including a chemokine receptor (CKR) gene cluster and a variety of human cancer-related gene loci. Other well-studied calcium binding proteins that contain EF-hand motifs include calmodulin (CaM), Troponin C, myosin regulatory light chain (MYL) and S-100 proteins