Mapping and consensus sequence identification for multiple vinculin binding sites within the talin rod.

The interaction between the cytoskeletal proteins talin and vinculin plays a key role in integrin-mediated cell adhesion and migration. Three vinculin binding sites (VBS1-3) have previously been identified in the talin rod using a yeast two-hybrid assay. To extend these studies, we spot-synthesized a series of peptides spanning all the alpha-helical regions predicted for the talin rod and identified eight additional VBSs, two of which overlap key functional regions of the rod, including the integrin binding site and C-terminal actin binding site. The talin VBS alpha-helices bind to a hydrophobic cleft in the N-terminal vinculin Vd1 domain. We have defined the specificity of this interaction by spot-synthesizing a series of 25-mer talin VBS1 peptides containing substitutions with all the commonly occurring amino acids. The consensus for recognition is LXXAAXXVAXX- VXXLIXXA with distinct classes of hydrophobic side chains at positions 1, 4, 5, 8, 9, 12, 15, and 16 required for vinculin binding. Positions 1, 8, 12, 15, and 16 require an aliphatic residue and will not tolerate alanine, whereas positions 4, 5, and 9 are less restrictive. These preferences are common to all 11 VBS sequences with a minor variation occurring in one case. A crystal structure of this variant VBS peptide in complex with the vinculin Vd1 domain reveals a subtly different mode of vinculin binding.