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. Swiprosin-2, also known as EFHD1 (EF-hand domain-containing protein D1), SWS2, PP3051 or MST133, is a 239 amino acid protein that contains two EF-hand domains and is expressed in a wide variety of tissues, including brain, liver, heart, kidney, testis, ovaries and spleen. Expression of Swiprosin-2, a possible calcium-binding protein, is upregulated during neuronal differentiation, suggesting a role for Swiprosin-2 in brain development and maturation.