arXiv subjects

T. Erdmann

Publications and source records attributed to T. Erdmann.

6 recordsLinked to original sources

arXiv2007

Dynamic force spectroscopy on multiple bonds: experiments and model

We probe the dynamic strength of multiple biotin-streptavidin adhesion bonds under linear loading using the biomembrane force probe setup for dynamic force spectroscopy. Measured rupture force histograms are compared to results from a master equation model for the stochastic dynamics of bond rupture under load. This allows us to extract the distribution of the number of initially closed bonds. We also extract the molecular parameters of the adhesion bonds, in good agreement with earlier results from single bond experiments. Our analysis shows that the peaks in the measured histograms are not simple multiples of the single bond values, but follow from a superposition procedure which generates different peak positions.

q-bio.BM↗

arXiv2007

Impact of receptor-ligand distance on adhesion cluster stability

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.

cond-mat.soft↗

arXiv2006

Bistability of cell-matrix adhesions resulting from non-linear receptor-ligand dynamics

Bistability is a major mechanism for cellular decision making and usually results from positive feedback in biochemical control systems. Here we show theoretically that bistability between unbound and bound states of adhesion clusters results from positive feedback mediated by structural rather than biochemical processes, namely by receptor-ligand dissociation and association dynamics which depend non-linearly on mechanical force and receptor-ligand separation. For small cell-matrix adhesions, we find rapid switching between unbound and bound states, which in the initial stages of adhesion allows the cell to explore its environment through many transient adhesions.

q-bio.SC↗

arXiv2004

Stochastic dynamics of adhesion clusters under shared constant force and with rebinding

Single receptor-ligand bonds have finite lifetimes, so that biological systems can dynamically react to changes in their environment. In cell adhesion, adhesion bonds usually act cooperatively in adhesion clusters. Outside the cellular context, adhesion clusters can be probed quantitatively by attaching receptors and ligands to opposing surfaces. Here we present a detailed theoretical analysis of the stochastic dynamics of a cluster of parallel bonds under shared constant loading and with rebinding. Analytical solutions for the appropriate one-step master equation are presented for special cases, while the general case is treated with exact stochastic simulations. If the completely dissociated state is modeled as an absorbing boundary, mean cluster lifetime is finite and can be calculated exactly. We also present a detailed analysis of fluctuation effects and discuss various approximations to the full stochastic description.

cond-mat.soft↗

arXiv2004

Adhesion clusters under shared linear loading: a stochastic analysis

We study the cooperative rupture of multiple adhesion bonds under shared linear loading. Simulations of the appropriate Master equation are compared with numerical integration of a rate equation for the mean number of bonds and its scaling analysis. In general, force-accelerated rupture is rather abrupt. For small clusters and slow loading, large fluctuations occur regarding the timepoint of final rupture, but not the typical shape of the rupture trajectory. For vanishing rebinding, our numerical results confirm three scaling regimes predicted before for cluster lifetime as a function of loading rate. For finite rebinding, the intermediate loading regime becomes irrelevant, and a sequence of two new scaling laws can be identified in the slow loading regime.

cond-mat.soft↗

arXiv2004

Stability of adhesion clusters under constant force

We solve the stochastic equations for a cluster of parallel bonds with shared constant loading, rebinding and the completely dissociated state as an absorbing boundary. In the small force regime, cluster lifetime grows only logarithmically with bond number for weak rebinding, but exponentially for strong rebinding. Therefore rebinding is essential to ensure physiological lifetimes. The number of bonds decays exponentially with time for most cases, but in the intermediate force regime, a small increase in loading can lead to much faster decay. This effect might be used by cell-matrix adhesions to induce signaling events through cytoskeletal loading.

cond-mat.soft↗