Molecular interactions between Pluronic F127 and the peptide tritrpticin in aqueous solution

Triblock copolymers, such as Pluronic F127 (F127), are pharmaceutically important amphiphilic compounds that self-assemble in aqueous solution either as discrete or entangled micelles, depending on their concentration and temperature, which may function as drug delivery vehicle. Herein, we have synthesized the antimicrobial peptide tritrpticin (TRP3), a tryptophan (Trp)- and arginine (Arg)-rich peptide, sequence VRRFPWWWPFLRR, with a broad spectrum of action against bacteria and fungi, to investigate its interaction with F127 in dilute aqueous solution, by using fluorescence and circular dichroism spectroscopies, differential scanning calorimetry, dynamic light scattering, and zeta potential methods. The combined results indicate that at 50 mu mol L-1 TRP3 and up to 700 mu mol L-1 F127, these compounds interact together to form F127-bound complexes with the peptide at low concentrations, and immobilized TPR3-containing micelle-like structures at higher concentrations. The F127-TRP3 complexes are stable with varying hydrodynamic size depending on the relative amount of F127, which can be tuned smaller by adjusting the copolymer concentration to values suitable for drug delivery applications in biomedicine.