Physiology and Biophysics Faculty

Research Interests

Many biological processes such as cell adhesion, cell-cell communication, and vesicle fusion, involve the interaction of apposing membranes. In my laboratory, we apply biophysical approaches toward understanding underlying mechanisms of membrane interactions. Three ongoing projects are:

(1) Relationship between ligand/receptor binding affinity and adhesion energy. A particularly interesting area of investigation is the regulation of cell adhesion in the immune response. Enhanced adhesion following T cell activation is mediated by dynamics of the lymphocyte function-associated antigen-1 (LFA-1)/ intercellular adhesion molecule 1 (ICAM-1) interaction. Equilibrium and kinetic binding studies have revealed that the affinity of LFA-1 for ICAM-1 increases 200-fold upon cell activation. These measurements raise the question of how adhesion and the equilibrium binding constant of a complex are related. To shed light on this subject, we developed an assay to measure the changes in adhesion energy of two surfaces in contact as a function of the equilibrium constant. The binding affinity dependence of adhesion energy can be described by two different regimes. At low binding affinity and low receptor density, adhesion energy increases linearly with the equilibrium dissociation constant, K_d. In the regime of high binding affinity and high receptor density, adhesion energy increases with the logarithm of K_d. Our analysis revealed that the LFA-1/ICAM-1 interaction belongs to the low affinity regime. Hence, a 200-fold increase in binding affinity may result in a significant increase in adhesion as observed.

(2) Mechanisms of cell de-adhesion. Another approach to investigating mechanisms of cell adhesion is to examine the applied force needed to induce T cell de-adhesion. One can envision two mechanisms for cell de-attachment. If tension is distributed equally among the adhesion complexes, one might expect a large build up in tension before a cooperative rupture of the complexes. At the other extreme, de-adhesion may involve a prolonged sequential breakage of the individual adhesion complexes. To explore these possibilities, we have initiated experiments that use the atomic force microscope (AFM) to measure force transients during the cell de-attachment process.

(3) Unbinding force of individual ligand-receptor complexes. At low receptor density, it is possible to detect the forced unbinding of individual complexes with AFM. In studies carried out in the avidin-biotin system, the dynamic response of the avidin-biotin bond displayed viscoelastic characteristics within the range of loading rate readily accessible by the AFM. In a comparison of different avidin-biotin analogs, the frictional drag of the ligand-receptor bond correlated with binding entropy change. At fast loading rates, the rupture force of the biotin complexes correlated with the enthalpy. Furthermore, the zero-point rupture force obtained by extrapolation to zero loading correlated with the equilibrium free energy.

• Google Scholar Citations
• PubMed Citations

Selected Publications

1. Eibl RH and Moy VT (2005) Atomic force microscopy measurements of protein-ligand interactions on living cells. Methods Mol Biol. 305:439-50.
2. Zhang X, Craig SE, Kirby H, Humphries MJ, Moy VT (2004) Molecular basis for the dynamic strength of the integrin alpha4beta1/VCAM-1 interaction. Biophys J. 87(5):3470-8.
3. Zhang X, Bogorin DF, Moy VT (2004) Molecular basis of the dynamic strength of the sialyl Lewis X--selectin interaction. Chemphyschem. 5(2):175-82.
4. Wojcikiewicz EP, Zhang X, Moy VT (2004) Force and Compliance Measurements on Living Cells Using Atomic Force Microscopy (AFM). Biol Proced Online 6:1-9.
5. Wojcikiewicz EP, Zhang X, Chen A, Moy VT (2003) Contributions of molecular binding events and cellular compliance to the modulation of leukocyte adhesion. J Cell Sci. 116(Pt 12):2531-9.
6. Li F, Redick SD, Erickson HP, Moy VT (2003) Force measurements of the alpha5beta1 integrin-fibronectin interaction. Biophys J. 84(2 Pt 1):1252-62.
7. Zhang X, Wojcikiewicz E, Moy VT (2002) Force spectroscopy of the leukocyte function-associated antigen-1/intercellular adhesion molecule-1 interaction. Biophys J. 83(4):2270-9. 
8. Yuan C, Chen A, Kolb P, Moy VT (2000) Energy landscape of streptavidin-biotin complexes measured by atomic force microscopy.  Biochemistry 39(33):10219-23.
9. Chen A and Moy VT (2000) Cross-linking of cell surface receptors enhances cooperativity of molecular adhesion. Biophys J. 78(6):2814-20.
10. Micic M, Chen A, Leblanc RM, Moy VT (1999) Scanning electron microscopy studies of protein-functionalized atomic force microscopy cantilever tips. Scanning 21(6):394-7.
11. Moy VT, Jiao Y, Hillmann T, Lehmann H, Sano T (1999) Adhesion energy of receptor-mediated interaction measured by elastic deformation. Biophys J. 76(3):1632-8.
12. Moy VT, Florin EL, and Gaub HE (1994) Intermolecular forces and energies between ligands and receptors. Science 266:257-259.
13. Florin EL, Moy VT, and Gaub HE (1994) Adhesion forces between individual ligand-receptor pairs. Science 264:415-417.

Curriculum Vitae

• 1984 B.A. Mathematics and Biophysics, University of Pennsylvania
• 1988 Ph.D. Chemistry, Stanford University
• 1988-1993 Postdoctoral Research Biochemist, Department of Chemistry, University of California at San Diego
• 1993-1995 Assistant in Physics, Physik-Department, Technische Universitīt Mnchen
• 1995-present Associate Professor, Dept. of Physiology and Biophysics, University of Miami School of Medicine