Quantifying the rebinding effect in multivalent chemical ligand-receptor systems.

Multivalent ligand-receptor systems often show an enhancement in binding compared to the constituent monovalent systems. This "cooperativity effect" is often attributed to the favorable spatial preorganisation of the ligands by the connecting spacer that leads to a reduction of entropy loss at ligand binding. A different factor that has been proposed to contribute to the cooperativity effect is "rebinding": As soon as a single ligand-receptor complex dissociates, the presence of another ligand "on coat-tails" will increase the probability of another binding event, which in turn will drive the system to a state where all ligands are bound. In this article, we derive a first quantitative description of the rebinding effect. In order to model the inherent memory effect of a spacer-connected system, we pursue a mathematical approach based on Markov state models and conformation dynamics. The theoretical investigations are illustrated by studying different prototypic ligand-receptor systems.