Effect of Point Mutations on the Aggregation Tendency of the Antimicrobial Fragment Peptide hLL-3717-29.

The aggregation of host defense peptides is directly linked to their membranolytic properties. A well-known example is the hLL-3717-29 peptide, where aggregation induces cell lysis. Mutations at the Ile24 position reduce antimicrobial potency; however, direct evidence connecting these mutations to altered aggregation propensities remains unknown. Here, we perform all-atom molecular dynamics simulations under NPT conditions to investigate the aggregation behavior of the wild-type (WT) peptide and five I24 mutants with hydrophobic (I24A), charged (I24D, I24K), or polar (I24Q, I24S) substitutions. All systems undergo rapid formation of small oligomers via hydrophobic collapse, followed by a biphasic aggregation process: an initial growth phase and a lag phase of structural reorganization. Among the mutants, I24D and I24Q are strongly aggregation-prone, I24K is aggregation-resistant, and the others show intermediate behavior. Transition network analysis reveals mutation-specific aggregation pathways that diverge from the dominant WT routes. Secondary structure analysis shows that mutations destabilize the amphipathic α-helix, especially in charged variants, with helix unfolding localized near the termini. Aggregate morphology remains predominantly fibrillar across systems, although internal order and packing specificity vary. Energetically, aggregation is governed by a balance between electrostatic and van der Waals forces, with mutation-dependent preferences. Preferential interaction parameters and hydrogen-bonding analyses highlight competition between peptide-peptide and peptide-water interactions in controlling aggregation. While I24K exhibits strong solvation and minimal aggregation, I24D forms hydrated yet highly aggregated clusters. Overall, these results underscore the nuanced interplay among sequence, structure, solvation, and aggregation in antimicrobial peptides, providing insights for the rational design of peptide-based materials and therapeutics.