Asylum Research AFM
 |
|
In the body, proteins carry out a remarkable number of mechanical functions ranging from the cytoskeletal network of cells to the adhesive "glue" that holds soft tissues together. In these instances, these proteins are designed to resist force or to respond to mechanical forces in particular ways. It is increasingly clear that the mechanical properties of proteins are as important to function as their binding affinities. However, the physical principles that determine the tensile strength of a protein bond are not necessarily the same as those determining the equilibrium binding energy between receptors and ligands.
Recent theoretical and experimental advances in single molecule mechanics are generating profound changes in our understanding of the links between physics, chemistry, and the mechanical properties of biological molecules. These nanoscale investigations are uncovering the bases of molecular recognition and the inner workings of protein nanomachines.
A major effort in my lab is aimed at determining the physical principles defining the links between biomolecular structure, the molecular mechanics of single proteins, and cell adhesion. We are particularly interested in critical adhesion proteins that are involved in development and in human disease. The aim of this work is to determine how structure determines the mechanical functions of these proteins. In particular, how do changes or mutations in their structures affect their function and ultimately lead to human disease.
Using these approaches, my lab was the first to discover a novel mechanism by which some adhesion proteins zip cell membranes together. Recent studies with other proteins from different structural families showed that an adhesion protein in the nervous system form either of two different bound states, which may play a role in organizing intercellular junctions. We also showed at the molecular level how post-translational modification can regulate adhesive function and lead to greater plasticity or even cancer in the nervous system.
Molecular mechanics measurements
My lab is using single molecule mechanics measurements to define the relationships
between the chemistry and mechanical strength of single proteins or protein
bonds. With techniques such as AFM we are exploring how molecular architecture
determines the kinetics, energies, and tensile strengths of essential biological
linkages. We further complement these measurements with Steered Molecular Dynamics
simulations to gain key insights into the atomic level interactions that underlie
our experimental observations. To determine how the behavior of individual molecules
translates to the collective behavior of hundreds of proteins between cell membranes,
we carry out Surface Force and cell adhesion measurements. Working with theory
groups, we are also developing theoretical models to bridge the gap between
single molecule mechanics and macroscopic adhesion.
|
Adhesion in the Immune System
One area of research in my group uses both Surface Force and AFM measurements
to investigate molecular recognition and adhesion in the immune system. In collaboration
with Anton van der Merwe at Oxford University, we are determining how the detailed
chemistry of protein-protein interfaces controls molecular recognition and determines
the strength of adhesion between T-cells and antigen presenting cells. We are
investigating members of the CD2 protein family as well as CD2 mutants, in order
to determine how the thermodynamic and kinetic parameters of CD2-ligand bonds
control binding between immune cells. We use the AFM and Steered Molecular Dynamics
simulations to determine how individual side chains define the energy landscapes
of the protein bonds. These in turn define the strength and dynamics of the
interaction. Surface force measurements provide the experimental link between
the single molecule behavior and the collective adhesive behavior of multiple
bonds between cell membranes.
Cadherin in inflammation, development, and disease
Cadherins are essential proteins that play a key role in directing the organization
of cells into tissues and organs. They also maintain the structural integrity
of all soft tissues in mature organisms. We are using a combination of single
molecule force probe studies, molecular dynamics simulations, surface force
measurements between membranes, and dynamic fluorescence measurements to determine
how these essential molecular building blocks assemble to form strong junctions
at cell-cell interfaces.
Cadherins also play an important role in inflammation. During the inflammatory response, cytokines trigger cellular changes that loosen the cadherin junctions between endothelial cells in the vascular system. This enables leukocytes to permeate and invade the surrounding tissues. In collaboration with a team in the Dept. of Pharmacology at UI Chicago, we are exploring how both inflammatory and anti-inflammatory compounds alter the organization and strength of cadherin junctions between endothelial cells in the vascular system.
Combinatorial diversity in biological recognition and
adhesion
In our bodies, there are thousands of different tissue interfaces. In the brain,
for example, neurons make hundreds of precisely defined connections, but our
limited number of genes is insufficient to account for their precision and diversity.
In collaboration with A. Chiba (UI Urbana-Champaign), my lab is exploring how
splice variations in adhesion proteins alters protein function, mechanisms of
molecular recognition, and adhesion strength. This combinatorial approach to
functional diversity in vivo may provide important clues into how cells organize
into tissues and how we can harness similar principles to generate new bio-adhesives
with altered or tailored functions.
