The School of Molecular and Cellular Biology at the University of Illinois at Urbana-Champaign

Structural basis of cell adhesion. A major focus in my group is to determine the molecular basis of the fundamental interactions that control cell adhesion. Adhesive interactions between cells are essential to life, controlling morphogenesis, wound healing, and the immune response. We are determining the basic mechanisms underlying these critical interactions.

Adhesion proteins from the immunoglobulin and cadherin superfamilies have unusual structures that consist of multiple, tandem repeats of similar domains. My lab uses force measurements to determine the structure-function relationships of these complex molecules. My group discovered that cadherin, an essential protein in development, binds its receptor by an unusual mechanism involving multiple cadherin domains. Single molecule force measurements demonstrated that this mechanism regulates cell adhesion through both spatial (membrane spanning distances) and kinetic controls. These discoveries are altering current thinking about these proteins' structures and their mechanical function. Further studies are determining how these properties control the specificity and formation of cell-cell contacts.

This unusual binding mechanism is not unique to cadherin. The neural cell adhesion molecule (NCAM) also forms multiple adhesive bonds that involve different domains of the protein. Our unique findings resolved an apparent controversy regarding the molecular basis of NCAM adhesion. We also determined the mechanism by which the post-translational modification of NCAM by polysialic acid regulates cell adhesion.

My group's approach to studying cell adhesion proteins is unique. We obtain results that are complementary to structural data as well as information not provided by structures alone. Using these molecular force measurements, together with the complementary approaches described below, we are generating novel, fundamental answers to some of the most basic and important questions in biology-that is, how cells organize to form tissues.

Molecular basis of synaptic matchmaking. The limited number of adhesion proteins is insufficient to account for the variety of different tissue interfaces. There are thousands of specific neural connections in the brain. What controls this tremendous complexity? In collaboration with Akira Chiba, we are using force measurements to determine whether differential splicing of cadherins generates the combinatorial diversity required to form the numerous synaptic connections in the brain.

Structural Studies of Adhesion Proteins. We are using neutron and X-ray reflectivity studies to determine the configurations of adhesion proteins at membrane surfaces, and we are developing techniques to quantify how these proteins organize opposing cell membranes. X-ray reflectivity studies performed at the European Synchrotron Radiation Facility in Grenoble showed that cadherins are oriented and well-organized at membrane surfaces. Additionally, we are using neutron reflectivity (Institute Laue-Langevin, Grenble) to determine the configuration of membrane bound proteins and the organization of polysialic acid bound to NCAM.

Formation and Disassembly of Adhesion Junctions. Adhesive junctions are not static, but change in time. The kinetics and bond energies of the proteins comprising these interfaces as well as the membrane properties determine the rates of adhesive junction maturation and disruption. We are using fluorescence techniques to quantify how cadherins and other adhesion molecules regulate the assembly and stabilization of cell-cell junctions. With a group at UI Chicago, we are investigating the disruption of cadherin junctions between epithelial cells in the inflammatory response, and, conversely, are determining the impact of anti-inflammatory agents on the stability of cadherin junctions.

Stem Cell Differentiation. My lab has established a broad-based understanding of the physical chemical mechanisms that control cell interactions with their environment. In one collaborative program involving investigators in Animal Sciences, the Keck Center for Genomic Research, and Chemical and Biomolecular Engineering, we are using microfabrication methods to engineer extracellular environments to direct stem cell differentiation. These tools, together with gene expression profiles of both intact tissue and cultured cells, are being used to define the precise combinations of factors that elicit identical cell behavior as in vivo.

Discovery Platforms for Biological Research. We are also developing these powerful microfabrication tools for high throughput analyses of the combinations and dosages of different molecules that control cell behavior. Using neurons as a model system, we are determining the effects of different adhesion proteins and growth factors on the directional growth and signaling activity of these cells. These platforms are used to test the potency of adhesion protein fragments identified by molecular force measurements, providing powerful cell assays to complement biophysical studies.