Structural basis of syndecan-4 activation by fibronectin

Sticking, or adhesion, of cells, either to other cells or to the tissue proteins that surround them in the body, is a vital part of multicellular life. Adhesion is needed for holding the body together and for keeping cells in the right place. During the course of many diseases, adhesion is used by cells to move abnormally throughout the body. Consequently, drugs that control adhesion might be useful for treating cardiovascular diseases, asthma, cancer, bacterial infections and ulcers. The work proposed in this application uses a combination of techniques to solve the structure of some important adhesive proteins. If successful, the work will help us to understand more about how the molecules involved in adhesion work. It might also suggest ways to design drugs to control adhesion or to engineer tissues.

Adhesion receptor signalling is essential for maintaining tissue structure and controlling cell migration. Conversely, dysregulation of adhesion contributes to the progression of a wide range of diseases by disrupting tissue architecture and allowing aberrant cell trafficking. To mediate these functions, adhesion receptors control dynamic interactions between extracellular matrices and the contractile cytoskeleton. A long-standing challenge in the field is to understand how adhesion receptors convert ligand binding into the efficacious signals that regulate cell movement. Recent studies in this laboratory have focused on fibronectin (FN) as a model adhesion protein, and advanced our understanding of the structural basis and functional significance of its cell adhesive activity. FN mRNA undergoes complex alternative splicing and its various isoforms bind to, and activate, two types of receptor. In mesenchymal cells, members of the integrin family (including alpha5beta1 and alpha4beta1) synergise with the transmembrane proteoglycan syndecan-4 to induce signalling and control cytoskeletal architecture. This proposal builds on these advances, and focuses on the structural basis of FN interactions with the glycosaminoglycan (GAG) chains of syndecan-4. Its specific aims are: 1. To elucidate the specificity of syndecan-4-FN binding by: (a) Defining the effects of alternative splicing of the FN IIICS region on syndecan-4 activation (b) Determining the role of GAG side-chains in syndecan-4 activation by FN 2. To define the structural basis of syndecan-4-FN binding by: (a) Determining the three-dimensional structure of FN fragments encompassing the IIICS spliced segment (b) Determining the three-dimensional structure of FN-GAG complexes