Structure-Activity Study of an All-d Antimicrobial Octapeptide D2D

• Published in: Molecules (Basel, Switzerland) Switzerland), 2019-12, Vol.24 (24), p.4571
• Main Authors: Lone, Abdullah, Thomsen, Thomas T, Nielsen, Josefine Eilsø, Thulstrup, Peter W, Klitgaard, Rasmus N, Løbner-Olesen, Anders, Lund, Reidar, Jenssen, Håvard, Hansen, Paul R
• Format: Article
• Language: English
• Subjects: Acinetobacter baumannii - drug effects; Amino acids; Anti-Infective Agents - chemistry; Anti-Infective Agents - pharmacology; Antibiotics; Antiinfectives and antibacterials; Antimicrobial agents; Antimicrobial peptides; Bacteria; Bacteria - drug effects; Cations; Circular Dichroism; Colistin; Combinatorial analysis; Dose-Response Relationship, Drug; E coli; Erythrocytes; Escherichia coli - drug effects; Gram-positive bacteria; Hydrophobic and Hydrophilic Interactions; Hydrophobicity; Investigations; Microbial Sensitivity Tests; Molecular Structure; Oligopeptides - chemistry; Oligopeptides - pharmacology; Peptides; Pseudomonas aeruginosa - drug effects; Staphylococcus aureus - drug effects; Structure-Activity Relationship; Toxicity; X-Ray Diffraction
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules24244571

The increasing emergence of multi-drug resistant bacteria is a serious threat to public health worldwide. Antimicrobial peptides have attracted attention as potential antibiotics since they are present in all multicellular organisms and act as a first line of defence against invading pathogens. We have previously identified a small all-d antimicrobial octapeptide amide kk(1-nal)fk(1-nal)k(nle)-NH ( ) with promising antimicrobial activity. In this work, we have performed a structure-activity relationship study of based on 36 analogues aimed at discovering which elements are important for antimicrobial activity and toxicity. These modifications include an alanine scan, probing variation of hydrophobicity at lys and lys , manipulation of amphipathicity, N-and C-termini deletions and lys-arg substitutions. We found that the hydrophobic residues in position 3 (1-nal), 4 (phe), 6 (1-nal) and 8 (nle) are important for antimicrobial activity and to a lesser extent cationic lysine residues in position 1, 2, 5 and 7. Our best analogue , showed MICs of 4 µg/mL against , , and with a hemolytic activity of 47% against red blood cells. Furthermore, compound kills bacteria in a concentration-dependent manner as shown by time-kill kinetics. Circular dichroism (CD) spectra of and compounds - showed that they likely fold into α-helical secondary structure. Small angle x-ray scattering (SAXS) experiments showed that a random unstructured polymer-like chains model could explain and compounds , , , and . Solution structure of compound can be described with a nanotube structure model, compound can be described with a filament-like structure model, while compound can be described with both models. Lipid interaction probed by small angle X-ray scattering (SAXS) showed that a higher amount of compound (~50-60%) inserts into the bilayer compared to (~30-50%). still remains the lead compound, however compound is an interesting antimicrobial peptide for further investigations due to its nanotube structure and minor improvement to antimicrobial activity compared to .