Metal-Ion Interactions with Dodecapeptide Fragments of Human Cationic Antimicrobial Protein LL-37 [hCAP(134–170)]

Abstract

Isothermal titration calorimetry, circular dichroism (CD) techniques, and in silico analysis were used to determine potential metal binding sites in human cationic antimicrobial protein (hCAP) corresponding to overlapping the dodecapeptide sequences of hCAP(134–170) referred to as LL-37. The correct antibacterial action of LL-37 is closely related to its established unique structure. Disturbances in the LL-37 structure (e.g., unwanted presence of metal ions) lead to a radical change in its biological functions. Five fragments of the LL-37 [hCAP(134–170)], namely, hCAP(134–145) ( A1 ), hCAP(140–151) ( A2 ), hCAP(146–157) ( A3 ), hCAP(152–163) ( A4 ), and hCAP(159–170) ( A5 ), were taken into account and their affinity to Mn(II) and Zn(II) ions was rigorously assessed. We prove that only three of the investigated peptides ( A1 , A2 , and A5 ) are capable of forming thermodynamically stable complexes with metal ions. Additionally, based on density functional theory (DFT) calculations, we propose the most likely coordination modes of metal(II) to peptides as well as discuss the chemical nature of the interactions. Finally, we present the structural features of the strongest binding peptide, hCAP(159–170), responsible for the metal binding. The presented results provide important structural and thermodynamic information to understand the influence of some metal ions on the activity of hCAP(134–170).

The Role of the Unbinding Cycle on the Coordination Abilities of the Bi-Cyclopeptides toward Cu(II) Ions

“…The cyclization affects the stiffening of the structure [2] and allows the mimicry of the secondary structure of some protein fragments [3]. Moreover, the cyclic structure promotes the anchoring of metal ions by amino acid side chains [4]. Studies have proven that cyclic peptides show specificity in forming bonds with certain metal ions.…”