Structure of the free form of the N-terminal VH1 domain of monomeric α-catenin

The N-terminal vinculin-homology 1 (VH1) domain of α-catenin facilitates two exclusive forms, a monomeric form directly bound to β-catenin for linking E-cadherin to F-actin or a homodimer for the inhibition of β-catenin binding. Competition of these two forms is affected by ∼80 N-terminal residues, whose structure is poorly understood. We have determined the structure of the monomeric free form of the αN-catenin VH1 domain and revealed that the N-terminal residues form α1 and α2 helices to complete formation of the N-terminal four-helix bundle. Dynamic conformational changes of these two helices control formation of the β-catenin-bound monomer or unbound homodimer.