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

Area of Science:

• Supramolecular Chemistry
• Biophysical Chemistry
• Chemical Biology

Background:

• Cucurbit[7,8]urils (CB7, CB8) are macrocyclic hosts known for binding hydrophobic amino acids and N-terminal peptides.
• The interaction of histidine (His) with cucurbiturils is less understood, despite the importance of His in biological systems.

Purpose of the Study:

• To investigate the binding affinity and complexation behavior of histidine and histidine-containing peptides with CB7 and CB8.
• To explore the potential of using cucurbiturils for histidine-based biological applications.

Main Methods:

• X-ray diffraction experiments to elucidate the binding mode of histidine within the CB7 cavity.
• Isothermal titration calorimetry (ITC) to quantify binding affinities (equilibrium dissociation constants) of cucurbiturils with histidine-containing dipeptides.

Main Results:

• X-ray diffraction revealed a network of π-π and hydrogen bonds between two histidine moieties and CB7, inducing a significant pKa shift (ΔpKa=-4).
• Histidine alone showed weak binding to CB7 and CB8.
• ITC demonstrated micromolar binding affinities for CB7 and CB8 with C-terminal His dipeptides, contrasting with millimolar affinities for N-terminal His dipeptides.
• A 2:1 complex was observed between the His-Gly-Gly tripeptide and CB7.

Conclusions:

• Cucurbiturils exhibit specific binding preferences for histidine-containing peptides, particularly those with His at the C-terminus.
• The observed pKa shift and complex formation highlight the potential of CB7 and CB8 as tools for histidine recognition.
• Histidine and histidine-containing tags, in conjunction with cucurbiturils, offer promising avenues for diverse biological applications, including protein purification and sensing.