Abstract
Peptides isolated from combinatorial libraries typically interact with, and thus help to characterize, biologically relevant binding domains of target proteins. To characterize the binding domains of the focal adhesion protein vinculin, vinculin-binding peptides were isolated from two phage-displayed random peptide libraries. Altogether, five non-similar vinculin-binding peptides were identified. Despite the lack of obvious sequence similarity between the peptides, binding and competition studies indicated that all five interact with the talin-binding domain of vinculin and do not disrupt the binding of alpha-actinin or paxillin to vinculin. The identified peptides and talin bind to vinculin in a comparable manner; both bind to immobilized vinculin, but neither binds to soluble vinculin unless the C-terminus of vinculin has been deleted. An analysis of amino acid variants of one of the peptides has revealed three non-contiguous motifs that also occur in the region of talin previously demonstrated to bind vinculin. Amino acid substitutions within a 127-residue segment of talin capable of binding vinculin confirmed the importance of two of the motifs and suggest that residues critical for binding are within a 16-residue region. This study demonstrates that the vinculin-binding peptides interact with vinculin in a biologically relevant manner and represent an excellent tool for further study of the biochemistry of vinculin.