EF-hand proteins are a family of calcium-binding proteins that include important animal and plant allergens. An EF-hand is a specific amino acid motif in proteins. The name EF-hand originates from the nomenclature used in the study of parvalbumin, which has three EF-hand motifs. EF-hand refers to a structural motif of these proteins. The name is derived from the designation of the helices of these proteins, which are designated A-F. In EF-hand proteins (e.g., parvalbumins), two helices, the E and F helices, are arranged like the thumb and forefinger of the right hand; the loop lying between the E and F helices is the binding site where a Ca2+ is incorporated.
Many intracellular proteins that bind Ca2+ also show the EF-hand structural motif and belong to the EF-hand superfamily, including troponin C and calmodulin and S100 proteins.