EF-hand

Calcium ion binding site

Upon binding to Ca, this motif may undergo conformational changes that enable Ca-regulated functions as seen in Ca effectors such as calmodulin (CaM) and troponin C (TnC) and Ca buffers such as calreticulin and calbindin D9k. While the majority of the known EF-hand calcium-binding proteins (CaBPs) contain paired EF-hand motifs, CaBPs with single EF hands have also been discovered in both bacteria and eukaryotes. In addition, "EF-hand-like motifs" have been found in a number of bacteria. Although the coordination properties remain similar with the canonical 29-residue helix–loop–helix EF-hand motif, the EF-hand-like motifs differ from EF-hands in that they contain deviations in the secondary structure of the flanking sequences and/or variation in the length of the Ca-coordinating loop.