Selectivity of competitive multivalent interactions at interfaces.

The development of synthetic, low-molecular-weight ligand receptor systems for the selective control of biomolecular interactions remains a major challenge. Binding of oligohistidine peptides to chelators containing Ni2+-loaded nitrilotriacetic acid (NTA) moieties is one of the most widely used and best-characterised recognition systems. Recognition units containing multiple NTA moieties (multivalent chelator headgroups, MCHs) recognise oligohistidines with substantially increased binding affinities. Different multivalencies both at the level of the MCH and at that of the oligohistidine ligand provide a powerful means to vary the affinity of the interaction systematically. Here we have explored the selectivity for the binding of different oligohistidines to immobilised MCH. Using microarrays of mono-, bis-, tris- and tetrakis-NTA chelators spotted at different surface densities, we explored the ability of these binders to discriminate fluorescently labelled hexa- and decahistidine peptides. When hexa- and decahistidine were tested alone, the discrimination of ligands showed little dependence either on the nature or on the density of the chelator. In contrast, coincubation of both peptides decreased the affinity of hexahistidine, increased the affinity of decahistidine, and made the binding of decahistidine highly dependent on MCH density. Kinetic binding assays by dual-colour total internal reflection fluorescence spectroscopy revealed active exchange of His6 by His10 and confirmed the high selectivity towards His10. Our results establish the key role of surface multivalency for the selectivity of multivalent interactions at interfaces.