Biophys J, August 2002, p. 706-722, Vol. 83, No. 2

Multi-Bead-and-Spring Model to Interpret Protein Detachment Studied by AFM Force Spectroscopy

Csilla Gergely,^* Joseph Hemmerlé,^* Pierre Schaaf, J. K. Heinrich Hörber, Jean-Claude Voegel,^* and Bernard Senger^*

 ^*Institut National de la Santé et de la Recherche Médicale, Unité 424, UFR d'Odontologie, Université Louis Pasteur, 67085 Strasbourg Cedex, France;  Institut Charles Sadron, Centre National de la Recherche Scientifique, Université Louis Pasteur, 67083 Strasbourg Cedex, France;  European Molecular Biology Laboratory, 69012 Heidelberg, Germany

This article deals with the detachment of molecules (fibrinogen) from a surface studied experimentally with an atomic force microscope. The detachment (or rupture) forces are measured as a function of the retraction velocity and exhibit a clear dependence on this parameter, even though the interaction between the molecules and the surface are nonspecific. To interpret these data, a mechanical multi-bead-and-spring model is developed. It consists of one to several parallel, "molecular" springs connected to an extra spring representing the cantilever that is moved at constant velocity. The free end of each molecular spring terminates with a particle that interacts with the surface through a Lennard-Jones potential. This Brownian dynamics model is used to analyze the experimental findings. In the framework of this model, it appears that the fibrinogen molecule must be ascribed a stiffness much smaller than that of the cantilever. In addition, several bonds between the molecule and the surface must be taken into account for the range of the molecule-surface interaction not to be unrealistically small. In future work, this model will be extended to more complex mechanisms such as the detachment of cells from a surface.

Biophys J, August 2002, p. 706-722, Vol. 83, No. 2
© 2002 by the Biophysical Society   0006-3495/02/08/706/17  $2.00