How Unnatural Amino Acids in Antimicrobial Peptides Change Interactions with Lipid Model Membranes

• Published in: The journal of physical chemistry. B Vol. 128; no. 40; pp. 9772 - 9784
• Main Authors: Mitra, Saheli, Chen, Mei-Tung, Stedman, Francisca, Hernandez, Jedidiah, Kumble, Grace, Kang, Xi, Zhang, Churan, Tang, Grace, Daugherty, Ian, Liu, Wanqing, Ocloo, Jeremy, Klucznik, Kevin Raphael, Li, Alexander Anzhi, Heinrich, Frank, Deslouches, Berthony, Tristram-Nagle, Stephanie
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 10.10.2024
• Subjects: Amino Acids - chemistry; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - pharmacology; Antimicrobial Peptides - chemistry; Antimicrobial Peptides - pharmacology; B: Biomaterials and Membranes; Gram-Negative Bacteria - drug effects; Gram-Positive Bacteria - drug effects; Humans; Microbial Sensitivity Tests
• ISSN: 1520-6106; 1520-5207; 1520-5207
• DOI: 10.1021/acs.jpcb.4c04152

This study investigates the potential of antimicrobial peptides (AMPs) as alternatives to combat antibiotic resistance, with a focus on two AMPs containing unnatural amino acids (UAAs), E2-53R (16 AAs) and LE-54R (14 AAs). In both peptides, valine is replaced by norvaline (Nva), and tryptophan is replaced by 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic). Microbiological studies reveal their potent activity against both Gram-negative (G(−)) and Gram-positive (G­(+)) bacteria without any toxicity to eukaryotic cells at test concentrations up to 32 μM. Circular dichroism (CD) spectroscopy indicates that these peptides maintain α-helical structures when interacting with G(−) and G­(+) lipid model membranes (LMMs), a feature linked to their efficacy. X-ray diffuse scattering (XDS) demonstrates a softening of G(−), G­(+) and eukaryotic (Euk33) LMMs and a nonmonotonic decrease in chain order as a potential determinant for bacterial membrane destabilization. Additionally, XDS finds a significant link between both peptides’ interfacial location in G(−) and G­(+) LMMs and their efficacy. Neutron reflectometry (NR) confirms the AMP locations determined using XDS. Lack of toxicity in eukaryotic cells may be related to their loss of α-helicity and their hydrocarbon location in Euk33 LMMs. Both AMPs with UAAs offer a novel strategy to wipe out antibiotic-resistant strains while maintaining human cells. These findings are compared with previously published data on E2-35, which consists of the natural amino acids arginine, tryptophan, and valine.