Ankyrin repeat - ANK

The ankyrin repeat is one of the most common protein-protein interaction motifs in nature. Ankyrin repeats are tandemly repeated modules of about 33 amino acids. They occur in a large number of functionally diverse proteins mainly from eukaryotes. The few known examples from prokaryotes and viruses may be the result of horizontal gene transfers. The repeat has been found in proteins of diverse function such as transcriptional initiators, cell-cycle regulators, cytoskeletal, ion transporters and signal transducers. The ankyrin fold appears to be defined by its structure rather than its function since there is no specific sequence or structure which is universally recognised by it. Each repeat folds into a helix-loop-helix structure with a beta-hairpin/loop region projecting out from the helices at a 90 degree angle. The repeats stack together to form an L-shaped structure