Structure–function relationships and rational optimisation of amphibian skin-derived antimicrobial peptides

Abstract

Antimicrobial resistance is a major global health threat that demands alternatives to conventional antibiotics. Amphibian skin-derived antimicrobial peptides (AMPs) are promising therapeutic candidates due to their broad-spectrum antimicrobial activity, rapid bactericidal effects, and multifunctional biological properties. However, their clinical application is often limited by insufficient selectivity, cytotoxicity, and incomplete mechanistic understanding.

This thesis investigated the discovery, optimisation, and mechanistic characterisation of amphibian-derived AMPs using integrated experimental and computational approaches. A novel peptide, QUB-3301, isolated from Odorrana grahami, demonstrated potent antimicrobial activity, particularly against Gram-negative bacteria, with moderate haemolytic toxicity. Rational sequence modification and structure–activity relationship analysis revealed that peptide length, amphipathicity, and stereochemistry critically influenced antimicrobial performance and selectivity. All-atom molecular dynamics simulations further provided atomic-level insight into peptide conformational stability, membrane insertion, and peptide–membrane interactions.

In parallel, a multifunctional peptide engineering strategy was explored using Senegalin-2. Fusion with a bradykinin-derived sequence generated Senegalin-2BK, which exhibited enhanced antimicrobial and antibiofilm activities, reduced haemolytic toxicity, and retained smooth muscle bioactivity. Transcriptomic analysis of peptide-treated bladder epithelial cells showed modulation of pathways associated with inflammation, epithelial barrier integrity, and immune signalling, suggesting host-defence–like immunomodulatory potential.

Additionally, the histamine-releasing peptide Kassinakinin-S was rationally truncated and optimised to generate analogues with improved antimicrobial activity and altered physicochemical properties. Molecular dynamics simulations demonstrated that truncation reshaped peptide conformation and membrane interaction behaviour.

Overall, this work establishes a comprehensive structure–function framework for amphibian-derived AMPs by integrating peptide design, bioactivity evaluation, molecular dynamics simulations, and systems-level biological analysis. The findings provide mechanistic insight into peptide–membrane interactions, identify effective optimisation strategies, and support the development of next-generation peptide-based anti-infective therapeutics.

Thesis is embargoed until 31 July 2031.

Date of Award	Jul 2026
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Tianbao Chen (Supervisor), Mei Zhou (Supervisor) & Chengbang Ma (Supervisor)