An armadillo repeat is a characteristic, repetitive
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
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 cal ...
of about 42
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 structure.
Examples of proteins that contain armadillo repeats include
β-catenin, Sarm1 (
SARM1),
α-importin,
,
(APC),
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
Cadherins (named for "calcium-dependent adhesion") are cell adhesion molecules important in forming adherens junctions that let cells adhere to each other. Cadherins are a class of type-1 transmembrane proteins, and they depend on calcium (Ca2+) ...
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
β-catenin 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 ...
branching and bundling.
[Nusse, Roel, and Hans Clevers. “Wnt/β-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 during
embryonic development
In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermat ...
.
Structure
The 3-dimensional fold of an armadillo repeat was first observed in the crystal structure of
β-catenin, where the 12
tandem repeats form a superhelix of
alpha helices 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
β-catenin.
References
External links
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Armadillo/plakoglobin ARM repeatin
PROSITE
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