Chemical and biological properties of a supramolecular complex of tuftsin and cucurbit[7]uril

- The binding tuftsin with CB7 was studied by competitive fluorescent titration.
- Quantum chemical calculations was used for structure interpretation.
- Cucurbit[7]uril binds peptide tuftsin with moderate affinity.
- Experimental results indicated a 1:1 host-guest inclusion complex formed.
- Tuftsin-CB7 complex increased the production of TNFα, IL2, IFNγ, and IL10 in vitro.

Cucurbit[7]uril (CB7) is an uncharged and water-soluble macrocyclic host. CB7 binds to doubly protonated tuftsin, which is the tetrapeptide Thr-Lys-Pro-Arg, with moderate affinity (Ka = 2.1 × 103 M− 1). In this study, the host-guest complexation was confirmed by fluorescence titration. This affinity would allow for easy release of the peptide under physiological conditions. According to density functional theory calculations, the structural binding motif involves hydrogen bonding. The most energetically stable form had the Arg side chain inside the CB7 cavity. The effects of the tuftsin-CB7 complex on the proliferation and cytokine activity of immune cells were studied. The complex had broader spectrum immunomodulation than free peptides, and caused statistically significant (p < 0,05) changes in cytokine production (tumor necrosis factor-α, interleukin-2, interferon-γ, and interleukin-10) by mononuclear cells. By contrast, the free peptide only activated tumor necrosis factor-α production.