Probing the binding selected metal ions and biologically active substances to the antimicrobial peptide LL-37 using DSC, ITC measurements and calculations

Abstract

Differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC) techniques have been used to describe physicochemical properties of polypeptide LL-37. LL-37 is a 37-residue, amphipathic, helical peptide, the only cathelicidin-derived antimicrobial peptide found in the human organism. Thermal stability of the LL-37 peptide in a water solution was measured by DSC over the 288.15–333.15 K range. Furthermore, the ITC method supported by theoretical calculations (peptide–ligand docking) were used to study the interactions between LL-37 and some divalent metal ions, namely Cu2+, Zn2+, and Ni2+ ions as well as acetylsalicylic acid, ascorbic acid, and caffeine molecules. It has been proven that under experimental conditions, the LL-37 peptide reveals affinity only toward Cu2+ and Zn2+ ions. The stoichiometry, conditional binding constants, logKITC, and thermodynamic parameters (∆ITCG, ∆ITCH, T∆ITCS) of the resulting Cu(II) and Zn(II) complexes were determined and discussed.