The catenins are a class of cytoplasmic proteins that are ubiquitously expressed.
They are found in complexes with cadherins and link them to the cytoskeleton.
The name "catenin" was originally selected because 'catena' means 'chain' in Latin.
Types
Alpha catenin is a 102 kDa actin-binding protein at the adherens junction. It attaches the microfilaments and associated proteins ( vinculin, alpha-actinin) to the transmembrane cell adhesion molecules, cadherins, via β-catenin.
The amino acid sequence of alpha-catenin has sequence similarity to that of vinculin.
There are three human alpha-catenin genes on different chromosomes
Beta catenin is a 94 kDa component of cell-cell adhesion.
It is a member of the armadillo family of proteins. These proteins have multiple copies of the so-called armadillo repeat domain which is specialized for protein-protein binding.
Beta catenin is found in at least 3 cellular pools:
- adherent junctions in association with the transmembrane receptor, E-cadherin, and the cytoskeletal linker, alpha-catenin
- cytoplasm
- nucleus in association with other trascription factor
β-catenin roles:
- β-catenin is a subunit of the cadherin protein complex.
It binds to both the C-terminus of the cadherin intracellular domain and the N-terminus of α-catenin, linking cadherin receptors to the cytoskeleton.
When beta-catenin is not associated with cadherins and alpha-catenin, it can interact with several different proteins inside cells. The interaction is often regulated by the reversible attachment of phosphate.
- β-catenin is also a protooncogene and take part of the Wnt/β-catenin/ Tcf signalling pathway that controls numerous events in development, including differentiation, proliferation and morphogenesis.
Delta-catenin belongs to the p120-catenin (p120ctn) protein family, which is characterized by ten, characteristically spaced Armadillo repeats that bind to the juxtamembrane segment of the classical cadherins. d-catenin is the only member of this family that is expressed specifically in neurons. As a component of both adherens and synaptic junctions, d-catenin can link the adherens junction to the synapse and, thereby, coordinate synaptic input with changes in the adherens junction. [1]
Plakophilins 1–3 are members of the p120ctn family of armadillo-related proteins. The plakophilins have been characterized as desmosomal proteins, they are essential components that interact with desmosomal cadherins as well as the cytoskeletal linker protein desmoplakin. Plakophilins stabilize desmosomal proteins at the plasma membrane. The three plakophilins reveal distinct expression patterns, and although partially redundant in their function, mediate distinct effects on desmosomal adhesion. [2]