Armadillo repeat
An armadillo repeat is a characteristic, repetitive amino acid sequence of about 42 residues in length that is found in many proteins. Proteins that contain armadillo repeats typically contain several Protein [tandem repeats|tandemly repeated] copies. Each armadillo repeat is composed of a pair of alpha helices that form a hairpin structure. Multiple copies of the repeat form what is known as an alpha solenoid structure.
Examples of proteins that contain armadillo repeats include β-catenin, Sarm1, α-importin, plakoglobin, adenomatous polyposis coli, and many others.
The term armadillo derives from the historical name of the β-catenin gene in the fruitfly Drosophila, where the armadillo repeat was first discovered. Although β-catenin was previously believed to be a protein involved in linking cadherin cell adhesion proteins to the cytoskeleton, recent work indicates that β-catenin regulates the homodimerization of alpha-catenin, which in turn controls actin branching and bundling. But, the armadillo repeat is found in a wide range of proteins with other functions. This type of protein domain is important in transducing WNT signals during embryonic development.