AVS 47th International Symposium
    Biomaterial Interfaces Thursday Sessions
       Session BI+NS-ThM

Invited Paper BI+NS-ThM5
Single-Molecule Protein-Ligand Bond-Rupture Forces Measured Using the Poisson Atomic Force Method

Thursday, October 5, 2000, 9:40 am, Room 202

Session: Nanoscale Biology
Presenter: T.P. Beebe, Jr., University of Utah
Authors: Y.-S. Lo, University of Utah
Y.J. Zhu, University of Utah
J.D. McBride, University of Utah
T.P. Beebe, Jr., University of Utah
Correspondent: Click to Email
It is known that bond strength is a dynamic property that is dependent upon the force loading rate applied during the rupturing of a bond. For biotin-avidin and biotin-streptavidin systems, dynamic force spectra, which are plots of bond strength vs. ln(loading rate), have been acquired in a recent biomembrane force probe (BFP) study [Merkel et al., Nature 397 (1999) 50] at force loading rates in the range of 0.05 to 60,000 pN/s. In the present study, the dynamic force spectrum of the biotin-streptavidin bond strength in solution was extended from loading rates of ~10@super 5@ to ~10@super 9@ pN/s with the atomic force microscope (AFM). The Poisson AFM statistical analysis method was applied to extract the magnitude of individual bond-rupture forces and non-specific long-range interactions from the AFM force-distance curve measurements. In addition, surface characterization methods for the analysis of protein-coated surfaces and AFM tips, both imaging and spectroscopic x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) will be discussed. The AFM bond strengths were found to scale linearly with the logarithm of the loading rate in two regimes with two different slopes, consistent with the view that multiple energy barriers are present along the unbinding coordinate of the biotin-streptavidin complex. In contrast, the non-specific interactions, which can be separately measured and characterized apart from the specific bond-rupture forces in this method, did not exhibit a measurable dependence on loading rate. The dynamic force spectra acquired here with the AFM combined well with BFP measurements by others, and demonstrated that unbinding forces measured by different techniques are in agreement and can be used together to obtain a dynamic force spectrum covering 11 orders of magnitude in loading rate.