Crystal structure of the M-fragment of α-catenin:: implications for modulation of cell adhesion

The cytoskeletal protein alpha -catenin, which shares structural similarity with vinculin, is required for cadherin-mediated cell adhesion, and functions to modulate cell adhesive strength and to link the cadherins to the actin-based cytoskeleton. Here we describe the crystal structure of a region of alpha -catenin (residues 377-633) termed the M-fragment. The M-fragment is composed of a tandem repeat of two antiparallel four-helix bundles of virtually identical architectures that are related in structure to the dimerization domain of (alpha -catenin and the tail region of vinculin. These results suggest that (alpha -catenin is composed of repeating antiparallel helical domains. The region of (alpha -catenin previously defined as an adhesion modulation domain corresponds to the C-terminal four-helix bundle of the M-fragment, and in the crystal lattice these domains exist as dimers. Evidence for dimerization of the M-fragment of alpha -catenin in solution was detected by chemical crosslinking experiments. The tendency of the adhesion modulation domain to form dimers may explain its biological activity of promoting cell-cell adhesiveness by inducing lateral dimerization of the associated cadherin molecule.