Armadillo repeat

An armadillo repeat is the name of a characteristic, repetitive amino acid sequence of about 40 residues in length that is found in many proteins. Proteins that contain armadillo repeats typically contain several tandemly repeated copies.[2][3] 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.

Armadillo repeat domain
Structure of the 5armadillo domain of beta-catenin.[1]
Identifiers
SymbolArm
PfamPF00514
Pfam clanCL0020
InterProIPR000225
SMARTSM00185
PROSITEPS50176
SCOPe3bct / SUPFAM
CDDcd00020
Membranome350

Examples of proteins that contain armadillo repeats include β-catenin, α-importin,[4] plakoglobin,[5] adenomatous polyposis coli (APC),[6] 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 act branching and bundling.[7] 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.

Structure

The 3-dimensional fold of an armadillo repeat was first observed in the crystal structure of beta-catenin, where the 12 tandem repeats form a superhelix of alpha helices with three helices per unit.[1] The cylindrical structure features a positively charged groove, which presumably interacts with the acidic surfaces of the known interaction partners of beta-catenin.[8]

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References
  1. Huber AH, Nelson WJ, Weis WI (September 1997). "Three-dimensional structure of the armadillo repeat region of beta-catenin". Cell. 90 (5): 871–82. doi:10.1016/S0092-8674(00)80352-9. PMID 9298899.
  2. Peifer M, Berg S, Reynolds AB (1994). "A repeating amino acid motif shared by proteins with diverse cellular roles". Cell. 76 (5): 789–91. doi:10.1016/0092-8674(94)90353-0. PMID 7907279.
  3. Groves MR, Barford D (1999). "Topological characteristics of helical repeat proteins". Current Opinion in Structural Biology. 9 (3): 383–9. doi:10.1016/S0959-440X(99)80052-9. PMID 10361086.
  4. Herold A, Truant R, Wiegand H, Cullen BR (October 1998). "Determination of the functional domain organization of the importin alpha nuclear import factor". J. Cell Biol. 143 (2): 309–18. doi:10.1083/jcb.143.2.309. PMC 2132842. PMID 9786944.
  5. McCrea PD, Turck CW, Gumbiner B (November 1991). "A homolog of the armadillo protein in Drosophila (plakoglobin) associated with E-cadherin". Science. 254 (5036): 1359–61. doi:10.1126/science.1962194. PMID 1962194.
  6. Hirschl D, Bayer P, Müller O (March 1996). "Secondary structure of an armadillo single repeat from the APC protein". FEBS Lett. 383 (1–2): 31–6. doi:10.1016/0014-5793(96)00215-3. PMID 8612785.
  7. 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.
  8. "Armadillo (IPR000225)". InterPro. EMBL-EBI.


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