The Mechanism of Action of SAAP-148 Antimicrobial Peptide as Studied with NMR and Molecular Dynamics Simulations

Abstract

Background: SAAP-148 is an antimicrobial peptide derived from LL-37. It exhibits excellent activity against drug-resistant bacteria and biofilms while resisting degradation in physiological conditions. Despite its optimal pharmacological properties, its mechanism of action at the molecular level has not been explored. Methods: The structural properties of SAAP-148 and its interaction with phospholipid membranes mimicking mammalian and bacterial cells were studied using liquid and solid-state NMR spectroscopy as well as molecular dynamics simulations. Results: SAAP-148 is partially structured in solution and stabilizes its helical conformation when interacting with DPC micelles. The orientation of the helix within the micelles was defined by paramagnetic relaxation enhancements and found similar to that obtained using solid-state NMR, where the tilt and pitch angles were determined based on 15N chemical shift in oriented models of bacterial membranes (POPE/POPG). Molecular dynamic simulations revealed that SAAP-148 approaches the bacterial membrane by forming salt bridges between lysine and arginine residues and lipid phosphate groups while interacting minimally with mammalian models containing POPC and cholesterol. Conclusions: SAAP-148 stabilizes its helical fold onto bacterial-like membranes, placing its helix axis almost perpendicular to the surface normal, thus probably acting by a carpet-like mechanism on the bacterial membrane rather than forming well-defined pores.

Comparative analysis of a POPC bilayer and a DPC micelle comprising an interfacial anchored peptide using all-atom MD simulations

“…Side-chain RMSD is 3.65 Å and 3 Å in the DPC micelle and the POPC bilayer respectively. This result is in good correlation with published data: (i) other molecular dynamics studies revealed that the antimicrobial peptides SAAP-148 [10] and hylaseptin-4 [13] stabilize their helical conformations when interacting with DPC micelles; (ii) circular dichroism data revealed helical structure for the antimicrobial peptide anoplin when interacting with DPC micelle and POPC:POPG liposomes [40].…”

“…Concerning the interactions between interfacial anchored peptides and POPC bilayers or DPC micelles, most of the experimental studies give atomic description of the peptide structure. Only in few studies, the specific interactions between the peptide and the DPC or POPC molecules are described [9,10]. Indeed, such experimental information is scarce due essentially to the unfavourable dynamics of the systems, especially at the membrane interface where the dynamics of the lipid head groups is important.…”

Bactericidal Activity to Escherichia coli: Different Modes of Action of Two 24-Mer Peptides SAAP-148 and OP-145, Both Derived from Human Cathelicidine LL-37

“…Further studies are necessary to elucidate the specific mechanisms and contributions of these interactions in the antimicrobial and immunomodulatory activities of these peptides. Although both peptides are alpha helical [32,53], further studies are needed to elucidate differences in amphipathicity and stability of alpha helices with respect to membrane-peptide interactions.…”