EFCAB4A, also known as Calcium release-activated calcium channel regulator 2B, is a novel Ca2+-binding EF-hand protein that is thought to play a key role in store-operated Ca2+ entry in T-cells by regulating CRAC channel activation, but the detailed function is still under investigation. It is likely to play a similar role as the related protein EFCAB4B, which acts as a cytoplasmic calcium-sensor that forms a complex with ORAI1 and STIM1 at the junctional regions between the plasma membrane and the endoplasmic reticulum upon low Ca2+ concentration.