Berlin 2005 – scientific programme

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AKB: Biologische Physik

AKB 200: Poster Session II

AKB 200.21: Poster

Tuesday, March 8, 2005, 17:00–19:00, Poster TU C

Effect of receptor-ligand distance on adhesion cluster stability — •Thorsten Erdmann and Ulrich S. Schwarz — Max Planck Institute of Colloids and Interfaces, Theory Division, 14424 Potsdam

Cells in multicellular organisms adhere to the extracellular matrix through two-dimensional clusters of adhesion bonds. Single adhesion bonds have finite lifetimes and open and close stochastically. For many common receptor-ligand systems, the ligands are tethered to the substrate via polymeric spacers so that adhesion cluster stability crucially depends on receptor-ligand distance. Experimentally, the distance-dependent interplay of rupture and rebinding in adhesion clusters can be studied in vitro, e. g. by atomic force microscopy, the biomembrane force probe, or the surface force apparatus. In order to study this effect theoretically, we introduce a one-step master equation for the stochastic dynamics of parallel bonds. Binding requires stretching of the polymeric tether, which leads to a distance-dependent binding rate. Closed bonds correspond to stretched tethers and exert force on the receptors, which is counteracted by the elastic stiffness of the force transducer. This force accelerates unbinding, but it is also shared equally by all closed bonds. The formation of new bonds reduces receptor-ligand distance and increases the probability for further binding. These effects make receptor-ligand binding in adhesion clusters a cooperative and self-reinforcing process. A bifurcation analysis of a deterministic differential equation for the average number of closed bonds reveals the existence of a bistable region in which a bound and an unbound state coexist. In the stochastic treatment, the system continuously jumps between these two macrostates.