Impact of receptor-ligand distance on adhesion cluster stability
University of Heidelberg, Im Neuenheimer Feld 293, 69120, Heidelberg, Germany
* e-mail: Ulrich.Schwarz@iwr.uni-heidelberg.de
Published online: 9 March 2007
Cells in multicellular organisms adhere to the extracellular matrix through two-dimensional clusters spanning a size range from very few to thousands of adhesion bonds. For many common receptor-ligand systems, the ligands are tethered to a surface via polymeric spacers with finite binding range, thus adhesion cluster stability crucially depends on receptor-ligand distance. We introduce a one-step master equation which incorporates the effect of cooperative binding through a finite number of polymeric ligand tethers. We also derive Fokker-Planck and mean field equations as continuum limits of the master equation. Polymers are modeled either as harmonic springs or as worm-like chains. In both cases, we find bistability between bound and unbound states for intermediate values of receptor-ligand distance and calculate the corresponding switching times. For small cluster sizes, stochastic effects destabilize the clusters at large separation, as shown by a detailed analysis of the stochastic potential resulting from the Fokker-Planck equation.
PACS: 87.15.-v Biomolecules: structure and physical properties – / 82.39.-k Chemical kinetics in biological systems – / 05.10.Gg Stochastic analysis methods (Fokker-Planck, Langevin, etc.) –
© EDP Sciences/Società Italiana di Fisica/Springer-Verlag, 2007