Cucurbit[7]uril‐mediated Histidine Dimerization: Exploring the Structure and Binding Mechanism

Abstract

Cucurbit[7,8]urils are known to form inclusion complexes with hydrophobic amino acids such as Trp, Tyr, Phe, and Met, as well as peptides containing these residues at the N‐terminus. Despite their widespread use in protein purification, the affinity of histidine (His) for cucurbit[7,8]urils has not been extensively explored. In this study, X‐ray diffraction experiments were conducted to investigate the binding of two histidine moieties to the cucurbit[7]uril (CB7) cavity, resulting in a network of π–π and hydrogen bonds. This assembly was found to induce a His pKa shift of ΔpKa=−4. Histidine weakly bound to CB7 or CB8; however, isothermal titration calorimetry revealed micromolar equilibrium dissociation constant values for CB7 and CB8 when bound to dipeptides containing His at the C‐terminus. Conversely, dipeptides with His at the N‐terminus exhibited millimolar values. Additionally, the His‐Gly‐Gly tripeptide formed a 2 : 1 complex with CB7. These findings suggest the potential use of histidine and histidine‐containing tags in conjunction with CB7 for various biological applications.