Effects of Multiple-Bond Ruptures on Kinetic Parameters Extracted from Force Spectroscopy Measurements: Revisiting Biotin-Streptavidin Interactions

¹ Duke University

^* To whom correspondence should be addressed. E-mail: boris.a{at}duke.edu.

Submitted on March 20, 2008
Revised on May 5, 2008
Accepted on 19 June 2008

	Abstract

Force spectroscopy measurements of the rupture of the molecular bond between biotin and streptavidin often results in a wide distribution of rupture forces. We attribute the long tail of high rupture forces to the nearly simultaneous rupture of more than one molecular bond. To decrease the number of possible bonds we employed hydrophilic polymeric tethers to attach biotin molecules to the atomic force microscope (AFM) probe. It is shown that the measured distributions of rupture forces still contain high forces that cannot be described by the forced dissociation from a deep potential well. We employed a recently developed analytical model of simultaneous rupture of two bonds connected by polymer tethers with uneven length (Gu et al. 2008, J. Phys. Chem. C 112: 5085-5092) to fit the measured distributions. The resulting kinetic parameters agree with the energy landscape predicted by molecular dynamics simulations. It is demonstrated that when more that one molecular bond might rupture during the pulling measurements there is a noise-limited range of probe velocities where the kinetic parameters measured by force spectroscopy correspond to the true energy landscape. Outside of this range of velocities the kinetic parameters extracted by using the standard most probable force approach might be interpreted as artificial energy barriers that are not present in the actual energy landscape. Factors that affect the range of useful velocities are discussed.

Key Words: Fokker-Plank equation, dynamic force spectroscopy, multiple bond rupture, potential of mean force