Dresden 2006 – scientific programme

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AKB: Biologische Physik

AKB 11: Cell Adhesion I

AKB 11.2: Talk

Tuesday, March 28, 2006, 12:15–12:30, ZEU 260

Impact of receptor-ligand distance on adhesion cluster stability — •Thorsten Erdmann and Ulrich S. Schwarz — Center for Modelling and Simulation in the Biosciences (BIOMS), Universität Heidelberg, Im Neuenheimer Feld 293, 69120 Heidelberg, Germany

Cells adhere to substrates through two-dimensional clusters of weak adhesion bonds, which open and close stochastically. In many common receptor-ligand systems, the ligands are tethered to the substrate via polymeric spacers. Binding of tethered ligands depends crucially on receptor-ligand distance because it requires stretching of the polymers. Experimentally, the distance-dependent interplay of rupture and rebinding in adhesion clusters can be studied in vitro, e.g. in the surface forces apparatus. We study this effect theoretically using a one-step master equation for the stochastic dynamics of parallel bonds. The force exerted by stretched tethers is balanced by the elastic stiffness of the force transducer. The force accelerates rupture of ligands but it is shared equally by all closed bonds. Formation of new bonds reduces the receptor-ligand distance and increases the probability for further binding. Receptor-ligand binding in adhesion clusters is thus a cooperative and self-reinforcing process. A bifurcation analysis of the deterministic differential equation for the average number of closed bonds reveals the existence of a bistable region in which bound and unbound clusters coexist. Stochastically, the system fluctuates continuously between these two macrostates.