MOLECULAR RECOGNITION AT INTERFACES.
Unlike binding in solution, the interfacial environment can dramatically alter the molecular recognition of surface-bound ligands in a variety of contexts including biosensors, biomaterials, drug delivery, and biology. Surface forces and even the molecular length can alter the kinetics and binding affinities relative to solution phase interactions. Lateral mobility on membranes also affects apparent affinities, particularly for multi-valent receptors. We use different analytical and biophysical approaches to understand the fundamental mechanisms underlying these effects as well as design rules for materials that preserve the function of immobilized biomolecules or enhance, for example, pathogen recognition.
Surface forces apparatus measurements directly quantify how colloidal surface forces alter the recognition of immobilized ligands. A recent study published in PNAS determined how ligand density and lateral mobility, in concert with structural flexibility affects how proteins in immunity recognize and bind pathogens. We also determined how genetic variations alter pathogen recognition, in ways that correlate with differences in human susceptibility to viral infections.
PROTEIN STRUCTURE, BINDING AFFINITIES, AND ADHESION STRENGTH.
This aspect of our research uses multi-scale approaches to define relationships between molecular structure, mechanical strengths of protein bonds, binding kinetics, and cell adhesion. A combination of molecular dynamics simulations, single molecule force spectroscopy, cell binding measurements, and protein engineering uniquely identifies relationships between the protein-ligand bond chemistry, the strength and the dynamics of bond formation/rupture, and cell adhesion.
For example, atomistic simulations of the forced rupture of the bond between two adhesion proteins in the immune system identified key load bearing amino acids in the binding interface. The predicted critical bonds were experimentally verified by molecular force measurements simulation. These and similar findings are being used to determine how macromolecular structure governs mechanical function in cell adhesion and transmembrane information transfer.
As a model system, we focus on cell-cell adhesion proteins cadherins, which are critical for development and tissue generation. Cadherin dysfuction is linked to a number of human diseases. Surface Force Apparatus, Biomembrane Force Probe, and Atomic Force Microscopy measurements identified and characterized different cadherin binding interactions, and mapped them to different structural regions of the protein. Subsequent micropipette studies of cadherin-mediated binding kinetics between single cell pairs, we demonstrated that binding properties at the single molecule level govern both initial cell binding kinetics and intracellular signaling.