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
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 fash ...
structure.
Examples of proteins that contain armadillo repeats include
β-catenin
Catenin beta-1, also known as β-catenin (''beta''-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene.
β-Catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcr ...
, Sarm1 (
SARM1
Sterile alpha and TIR motif containing 1 Is an enzyme that in humans is encoded by the ''SARM1'' gene. It is the most Conserved sequence, evolutionarily conserved member of the Toll-Interleukin receptor, Toll/Interleukin receptor-1 (TIR) family. ...
),
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 compon ...
,
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 Down-regulation, negative regulator that controls beta-catenin concentrations and i ...
(APC),
and many others.
The term armadillo derives from the historical name of the
β-catenin
Catenin beta-1, also known as β-catenin (''beta''-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene.
β-Catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcr ...
gene in the fruitfly ''
Drosophila
''Drosophila'' (), from Ancient Greek δρόσος (''drósos''), meaning "dew", and φίλος (''phílos''), meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or p ...
'', where the armadillo repeat was first discovered. Although
β-catenin
Catenin beta-1, also known as β-catenin (''beta''-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene.
β-Catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcr ...
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
Catenin beta-1, also known as β-catenin (''beta''-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene.
β-Catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcr ...
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
In cellular biology, 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, pronounced "wint", is a portmanteau created from the ...
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
Catenin beta-1, also known as β-catenin (''beta''-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene.
β-Catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcr ...
, where the 12
tandem repeats
In genetics, tandem repeats occur in DNA when a pattern of one or more nucleotides is repeated and the repetitions are directly adjacent to each other, e.g. ATTCG ATTCG ATTCG, in which the sequence ATTCG is repeated three times.
Several protein ...
form a superhelix of
alpha helices
An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix).
The alpha helix is the most common structural arrangement in the secondary structure of proteins. It is also the most extreme type of l ...
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
Catenin beta-1, also known as β-catenin (''beta''-catenin), is a protein that in humans is encoded by the ''CTNNB1'' gene.
β-Catenin is a dual function protein, involved in regulation and coordination of cell–cell adhesion and gene transcr ...
.
References
External links
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Armadillo/plakoglobin ARM repeatin
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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