Exploring the Limits of Bivalency by DNA-Based Spatial Screening.

Multivalency can facilitate complex formation when monovalent receptor-ligand interactions are weak. However, enhanced binding of two multivalent binding partners should be avoidable, for example when bivalent receptors ought to utilize multimolecular interactions to cross-link binding partners. We herein report the first systematic study to assess the criteria deciding whether a bivalent system engages in bivalency-enhanced interactions or cross-linking. We used DNA-instructed self-assembly to arrange the cucurbit[7]uril-adamantane host-guest system in 70-360 Å distance. Measurements and statistical mechanics analyses revealed that the affinity gain is controlled by 1) the distance between recognition modules, 2) the scaffold flexibility, and, importantly, 3) the strength of the monovalent interaction. We show that the bivalency effect can extend beyond 150 Å and discuss how, on the contrary, weak monovalent interactions reduce the concentration threshold for cross-linking. The findings are of interest for inhibitor design.