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Influence of colloidal rotational dynamics on the rate of specific adhesion

A team from ESPCI Paris, managed to turn a super- paramagnetic colloidal beads system into a powerful analytical tool for studying the specific adhesion kinetics promoted by ligand-receptors pairs bounded to surfaces. The contribution of the Mcube team to this breakthrough was to provide an accurate theoretical and computational framework in order to interpret the experimental set of data in terms of microscopic dynamics. In [1] was derived the average association time between colloidal beads in a number of relevant limits, spanning from the single ligand-receptor case to many distributed ligands over the surface. We also provide justification for the scaling between the association coefficient kon and the number of active ligands. This approach was used to extract the effective capture radius of tethered biotin-streptavidin ligand-receptor pairs in the experiments reported in [2].

Figure 1. Schematic representation of a bridging connection developing between two rotating colloids. A spacer that provides for some exploration region carries the ligand. Adhesion occurs when a ligand finds and sticks to a receptor on the opposing surface.

Molecular recognition emerges at the nanometer scale, when the size of the interacting partners becomes sufficient to establish multiple competing mutual interactions between them (such as directional hydrogen bonding), resulting in an efficient discrimination between matching and mismatching ligand-receptor pairs. Open questions arise when it comes to understand these specific interactions beyond the chemical and shape complementarity framework (the lock and key paradigm of Emil Fischer). For instance, one may wish to understand the influence of the local mechanical properties and the contribution of the configurational entropy to the equilibrium affinity constant Ka of the interacting pair.

[1Lee, Nam-Kyung; Johner, A.; Thalmann, F; Cohen-Tannoudji, L.; Bertrand, E.; Baudry, J.; Bibette, J.; Marques, C. M., Ligand-Receptor Interactions in Chains of Colloids: When Reactions Are Limited by Rotational Diffusion., Langmuir, 24, 1296 (2008).

[2Cohen-Tannoudji, L.; Bertrand, E.; Baudry, J. ; Robic, C.; Goubault, C.; Pellissier, M.; Johner, A.; Thalmann, F; Lee, Nam- Kyung; Marques, C. M.; Bibette, J., Measuring the Kinetics of Biomolecular Recognition with Magnetic Colloids., Phys. Rev. Let., 100, 108301 (2008).