Membrane Interaction and Embedding of a Self-Assembled 4-Helix Bundle from the Antimicrobial hLL-37_17-29 Fragment

Amyloidogenic and antimicrobial peptides (AMPs) share structural and functional similarities, suggesting that AMPs may have evolved from aggregation-prone amyloidogenic precursors through selective incorporation of cationic residues. The core segment of the human AMP LL-37 (hLL-37_17-29) retains antimicrobial activity and self-assembles into ribbon-like fibrils of repeating four-helix bundles (4HBs) with a distinct cross-α architecture. As their function depends on membrane interactions, elucidating how cross-α amyloids bind and perturb membranes at the atomistic level remains essential yet unexplored. Here, we use atomistic molecular dynamics simulations to investigate how hLL-37_17-29 4HBs interact with membranes of different compositions. Specifically, we examine their behavior toward PE:PG (3:1) and PC:PG (7:3) membranes mimicking bacterial compositions, pure PC representing mammalian membranes, and pure PE as a control. Our simulations show that preassembled tetrameric 4HBs bind stably to anionic membranes in a face-down orientation, elongating upon adsorption while retaining their helical nature and cross-α arrangement. The loss of translational entropy during binding is compensated by releasing surface-bound ions, making the process thermodynamically favorable in anionic membranes. 4HB binding also increases membrane curvature in anionic bilayers and enhances lipid ordering within 10 Å of its vicinity. The free energy associated with 4HB insertion into the bilayer interior highlights a previously unrecognized "sense or disrupt" mode of membrane engagement. The exceptionally high energy barrier observed in PE:PG membranes (≈53 kcal/mol), together with the pronounced membrane curvature, suggests a sensing role of 4HBs toward Gram-negative bacterial membranes, while they act as disruptors for the others. We also explore de novo assembly by simulating initially dispersed peptides near bacterial membranes to investigate whether aggregation precedes binding. Our study provides a comprehensive view of cross-α amyloid interactions with membranes that can be leveraged in biomedical applications.