Biomedical subjects

Robert A Borgon

Publications and source records attributed to Robert A Borgon.

3 recordsLinked to original sources

PubMed2005

Structural dynamics of alpha-actinin-vinculin interactions.

Alpha-actinin and vinculin orchestrate reorganization of the actin cytoskeleton following the formation of adhesion junctions. alpha-Actinin interacts with vinculin through the binding of an alpha-helix (alphaVBS) present within the R4 spectrin repeat of its central rod domain to vinculin's N-terminal seven-helical bundle domain (Vh1). The Vh1:alphaVBS structure suggests that alphaVBS first unravels from its buried location in the triple-helical R4 repeat to allow it to bind to vinculin. alphaVBS binding then induces novel conformational changes in the N-terminal helical bundle of Vh1, which disrupt its intramolecular association with vinculin's tail domain and which differ from the alterations in Vh1 provoked by the binding of talin. Surprisingly, alphaVBS binds to Vh1 in an inverted orientation compared to the binding of talin's VBSs to vinculin. Importantly, the binding of alphaVBS and talin's VBSs to vinculin's Vh1 domain appear to also trigger distinct conformational changes in full-length vinculin, opening up distant regions that are buried in the inactive molecule. The data suggest a model where vinculin's Vh1 domain acts as a molecular switch that undergoes distinct structural changes provoked by talin and alpha-actinin binding in focal adhesions versus adherens junctions, respectively.

Actinin↗

PubMed2004

Crystal structure of human vinculin.

Alterations in the actin cytoskeleton following the formation of cell-matrix and cell-cell junctions are orchestrated by vinculin. Vinculin associates with a large number of cytoskeletal and signaling proteins, and this flexibility is thought to contribute to rapid dissociation and reassociations of adhesion complexes. Intramolecular interactions between vinculin's head (Vh) and tail (Vt) domains limit access of its binding sites for other adhesion proteins. While the crystal structures of the Vh and Vt domains are known, these domains represent less than half of the entire protein and are separated by a large central region of unknown structure and function. Here we report the crystal structure of human full-length vinculin to 2.85 A resolution. In its resting state, vinculin is a loosely packed collection of alpha-helical bundles held together by Vh-Vt interactions. The three new well ordered alpha-helical bundle domains are similar in their structure to either Vh (Vh2 and Vh3) or to Vt (Vt2) and their loose packing provides the necessary flexibility that allows vinculin to interact with its various protein partners at sites of cell adhesion.

Animals↗

PubMed2003

Vinculin activation by talin through helical bundle conversion.

Vinculin is a conserved component and an essential regulator of both cell-cell (cadherin-mediated) and cell-matrix (integrin-talin-mediated focal adhesions) junctions, and it anchors these adhesion complexes to the actin cytoskeleton by binding to talin in integrin complexes or to alpha-actinin in cadherin junctions. In its resting state, vinculin is held in a closed conformation through interactions between its head (Vh) and tail (Vt) domains. The binding of vinculin to focal adhesions requires its association with talin. Here we report the crystal structures of human vinculin in its inactive and talin-activated states. Talin binding induces marked conformational changes in Vh, creating a novel helical bundle structure, and this alteration actively displaces Vt from Vh. These results, as well as the ability of alpha-actinin to also bind to Vh and displace Vt from pre-existing Vh-Vt complexes, support a model whereby Vh functions as a domain that undergoes marked structural changes that allow vinculin to direct cytoskeletal assembly in focal adhesions and adherens junctions. Notably, talin's effects on Vh structure establish helical bundle conversion as a signalling mechanism by which proteins direct cellular responses.

Adherens Junctions↗