The cytoplasmic protein β-catenin is essential for both intercellular adhesion and intracellular Wnt signaling. Invertebrates have multiple genes to cover the multiple functions, but on page 339 Gottardi and Gumbiner propose that vertebrate cells make do with one gene by maintaining different pools of protein for the different roles. Different folding may distinguish the adhesion and proliferative signaling functions.
Cofractionation experiments showed that β-catenin that interacts with cadherin is in a heterodimer with α-catenin, but Wnt signaling induces a monomeric form of β-catenin that interacts with a transcription factor complex. After enriching for cadherins, β-catenin can be detected using antibodies to either NH2-terminal or COOH-terminal regions; but in the cadherin-free fraction only the NH2-terminal antibody binds. The team hypothesizes that the β-catenin protein is folded back on itself in its monomeric form and, as such, is available for transcription complex binding but not for adhesion duties.
Gottardi speculates that a post-translational modification is responsible for the conformational change but does not yet know what that modification is. Furthermore, she thinks this sort of molecular segregation may be a common mechanism cells use to allow one protein to do multiple jobs, without the more common function soaking up all the protein required for a temporally regulated one.