Activation of a vinculin-binding site in the talin rod involves re-arrangement of a five helix bundle
Talin is a conserved cytoskeletal protein consisting of two subdomains: the talin head and the talin rod. Talin physically connects integrins to the actin cytoskeleton and regulates the inside-out activation of integrins. Binding partners of the talin head include integrins, focal adhesion kinase (FAK) and phosphatidylinositol-4-phosphate 5 kinases type 1 gamma isoform (PIPK1gamma). Along the talin rod, two actin binding sites, one integrin binding site and a minimum of three vinculin-binding sites have so far been mapped.;Vinculin is a cytoskeletal protein, which localises to focal adhesions. It has a molecular weight of 120kDa and consists of two parts: the head and a C-terminal tail. The talin binding site is located in the vinculin head between residues 1-258 (Vh').;In this thesis, the crystal structures of talin rod fragments 482-655 and 482-789 are presented. The structures are classified and compared with structural homologues, demonstrating that the talin rod structural organisation resembles the vinculin tail, alpha-catenin and apolipoproteins A and E. Talin 482-655 is a five helix bundle and talin 656-789 a four helix bundle. All helices are amphipathic and the predicted vinculin-binding site 1 (VBS1) is found buried in the hydrophobic core of the 5-helix bundle of talin 482-655. With supporting evidence from the two structures, mutant binding studies, alanine substitution experiments, NMR spectroscopy, limited proteolysis and the crystal structure of Vh' in complex with talin 605-628, a mechanism involving extensive conformational changes for both talin and vinculin is proposed to be required, in order to achieve vinculin/talin interaction.