An armadillo repeat is the name of a characteristic, repetitive

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

sequence In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is calle ...

of about 40 residues in length that is found in many proteins. Proteins that contain armadillo repeats typically contain several 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 An alpha solenoid (sometimes also known as an alpha horseshoe or as stacked pairs of alpha helices, abbreviated SPAH) is a protein fold composed of repeating alpha helix subunits, commonly helix-turn-helix motifs, arranged in antiparallel fashi ...

structure. Examples of proteins that contain armadillo repeats include

β-catenin Catenin beta-1, also known as beta-catenin (β-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene. Beta-catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcriptio ...

, α-importin,

plakoglobin Plakoglobin, also known as junction plakoglobin or gamma-catenin, is a protein that in humans is encoded by the ''JUP'' gene. Plakoglobin is a member of the catenin protein family and homologous to β-catenin. Plakoglobin is a cytoplasmic compone ...

adenomatous polyposis coli Adenomatous polyposis coli (APC) also known as deleted in polyposis 2.5 (DP2.5) is a protein that in humans is encoded by the ''APC'' gene. The APC protein is a negative regulator that controls beta-catenin concentrations and interacts with E-c ...

(APC), and many others. The term armadillo derives from the historical name of the

gene in the fruitfly ''

Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...

'' where the armadillo repeat was first discovered. Although

was previously believed to be a protein involved in linking

cadherin Cadherins (named for "calcium-dependent adhesion") are a type of cell adhesion molecule (CAM) that is important in the formation of adherens junctions to allow cells to adhere to each other . Cadherins are a class of type-1 transmembrane proteins, ...

cell adhesion proteins to the

cytoskeleton The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compos ...

, recent work indicates that

regulates the homodimerization of alpha-catenin, which in turn controls

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of over ...

branching and bundling.Nusse, Roel, and Hans Clevers. “Wnt/Î²-Catenin Signaling, Disease, and Emerging Therapeutic Modalities.” Cell, vol. 169, no. 6, 1 June 2017, pp. 985–999., doi:10.1016/j.cell.2017.05.016. 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 The Wnt signaling pathways are a group of signal transduction pathways which begin with proteins that pass signals into a cell through cell surface receptors. The name Wnt is a portmanteau created from the names Wingless and Int-1. Wnt signaling p ...

during

embryonic development An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

Structure

The 3-dimensional fold of an armadillo repeat was first observed in the crystal structure of beta-catenin, where the 12

tandem repeats Tandem repeats occur in DNA when a pattern of one or more nucleotides is repeated and the repetitions are directly adjacent to each other. Several protein domains also form tandem repeats within their amino acid primary structure, such as armadil ...

form a superhelix of

alpha helices The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...

with three helices per unit. The cylindrical structure features a positively charged groove, which presumably interacts with the acidic surfaces of the known interaction partners of beta-catenin.

References

External links

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Armadillo/plakoglobin ARM repeat
in

PROSITE PROSITE is a protein database. It consists of entries describing the protein families, domains and functional sites as well as amino acid patterns and profiles in them. These are manually curated by a team of the Swiss Institute of Bioinformati ...

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