Structure and Activity of a Selective Antibiofilm Peptide SK-24 Derived from the NMR Structure of Human Cathelicidin LL-37

Abstract

The deployment of the innate immune system in humans is essential to protect us from infection. Human cathelicidin LL-37 is a linear host defense peptide with both antimicrobial and immune modulatory properties. Despite years of studies of numerous peptides, SK-24, corresponding to the long hydrophobic domain (residues 9–32) in the anionic lipid-bound NMR structure of LL-37, has not been investigated. This study reports the structure and activity of SK-24. Interestingly, SK-24 is entirely helical (~100%) in phosphate buffer (PBS), more than LL-37 (84%), GI-20 (75%), and GF-17 (33%), while RI-10 and 17BIPHE2 are essentially randomly coiled (helix%: 7–10%). These results imply an important role for the additional N-terminal amino acids (likely E16) of SK-24 in stabilizing the helical conformation in PBS. It is proposed herein that SK-24 contains the minimal sequence for effective oligomerization of LL-37. Superior to LL-37 and RI-10, SK-24 shows an antimicrobial activity spectrum comparable to the major antimicrobial peptides GF-17 and GI-20 by targeting bacterial membranes and forming a helical conformation. Like the engineered peptide 17BIPHE2, SK-24 has a stronger antibiofilm activity than LL-37, GI-20, and GF-17. Nevertheless, SK-24 is least hemolytic at 200 µM compared with LL-37 and its other peptides investigated herein. Combined, these results enabled us to appreciate the elegance of the long amphipathic helix SK-24 nature deploys within LL-37 for human antimicrobial defense. SK-24 may be a useful template of therapeutic potential.

Peptide Stability Is Important but Not a General Requirement for Antimicrobial and Antibiofilm Activity In Vitro and In Vivo

“…These two peptides also displayed similar hemolysis with comparable 50% hemolytic concentrations (HC 50 ). 37 Taken together, these results underscore comparable antimicrobial and hemolytic ability of GF-17 and 17BIPHE2, making them an ideal peptide pair for us to compare their antibiofilm capabilities in vitro and in vivo as well. Our study underscores that this requirement is determined by both the peptide concentration and the initial CFU in the culture.…”

“…However, peptide stability did not show a clear advantage in numerous in vitro experiments, including antimicrobial susceptibility assays (Tables and and S1), killing kinetics, and membrane permeabilization studies (Figure ). These two peptides also displayed similar hemolysis with comparable 50% hemolytic concentrations (HC 50 ) . Taken together, these results underscore comparable antimicrobial and hemolytic ability of GF-17 and 17BIPHE2, making them an ideal peptide pair for us to compare their antibiofilm capabilities in vitro and in vivo as well.…”

Efficiency of Antimicrobial Peptides Against Multidrug-Resistant Staphylococcal Pathogens

“…D-LL-37, an LL-37 derivative in which all amino acids are changed to the D-form, displayed protease-resistance properties while possessing biofilm-inhibition capacity equal to the L-peptide isomer LL-37 (inhibiting ~40% biofilm formation at a concentration of 10 μg/ml) and immunostimulatory activity and wound-healing properties on the host higher than the L-peptide ( Dean et al, 2011 ). SK-24, which corresponds to residues 9–32 of LL-37, demonstrated killing activity against S. aureus and Staphylococcal biofilm reduction, which was superior to LL-37 and several other derivatives ( Zhang et al, 2021 ). KE-18, a derivative corresponding to residues 15–32 of LL-37, showed significant biofilm prevention against S. aureus ( Luo et al, 2017 ).…”

Renovation as innovation: Repurposing human antibacterial peptide LL-37 for cancer therapy

“…The two helices are separated by a bend or break. Furthermore, it has been found that the discontinuation is found on the hydrophobic surface at S9, rather than the helix ( Figures 2B,C ) ( Wang, 2008 ; Zhang et al, 2021 ).…”