Inhibition of Melittin Activity Using a Small Molecule with an Indole Ring

We investigated D-amino acids as potential inhibitors targeting L-peptide toxins. Among the L- and D-amino acids tested, we found that D-tryptophan (D-Trp) acted as an inhibitor of melittin-induced hemolysis. We then evaluated various Trp derivatives and found that 5-chlorotryptamine (5CT) had the largest inhibitory effect on melittin. The indole ring, amino group, and steric hindrance of an inhibitor played important roles in the inhibition of melittin activity. Despite the small size and simple molecular structure of 5CT, its IC50 was approximately 13 mu g/mL. Fluorescence quenching, circular dichroism measurements, and size-exclusion chromatography revealed that 5CT interacted with Trp19 in melittin and affected the formation