Thermodynamic and Biophysical Analysis of the Membrane-Association of a Histidine-Rich Peptide with Efficient Antimicrobial and Transfection Activities

Abstract

LAH4-L1 is a synthetic amphipathic peptide with antimicrobial activity. The sequence of the 23 amino acid peptide was inspired by naturally occurring frog peptides such as PGLa and magainin. LAH4-L1 also facilitates the transport of nucleic acids through the cell membrane. We have investigated the membrane binding properties and energetics of LAH4-L1 at pH 5.5 with physical-chemical methods. CD spectroscopy was employed to quantitate the membrane-induced random coil-to-helix transition of LAH4-L1. Binding isotherms were obtained with CD spectroscopy as a function of the lipid-to-protein ratio for neutral and negatively charged membranes and were analyzed with both the Langmuir multisite adsorption model and the surface partition/Gouy-Chapman model. According to the Langmuir adsorption model each molecule LAH4-L1 binds 4 POPS molecules, independent of the POPS concentration in the membrane. This is supported by the surface partition/Gouy-Chapman model which predicts an electric charge of LAH4-L1 of z = 4. Binding affinity is dominated by electrostatic attraction. The thermodynamics of the binding process was elucidated with isothermal titration calorimetry. The ITC data revealed that the binding process is composed of at least three different reactions, that is, a coil-to-helix transition with an exothermic enthalpy of about -11 kcal/mol and two endothermic processes with enthalpies of ∼4 and ∼8 kcal/mol, respectively, which partly compensate the exothermic enthalpy of the conformational change. The major endothermic reaction is interpreted as a deprotonation reaction following the insertion of a highly charged cationic peptide into a nonpolar environment.

Ocellatin peptides from the skin secretion of the South American frog Leptodactylus labyrinthicus (Leptodactylidae): characterization, antimicrobial activities and membrane interactions

“…8). These results are very representative, since, in several cases, antimicrobial peptides that partition between membrane and aqueous environments usually present higher helicities in the presence of TFE:H 2 O mixtures, whereas moderate or small structural contents are observed in the presence of phospholipid vesicles, due to simultaneous contributions of aqueous random-coil and structured membrane-bound populations [13, 48]. In the presence of POPC, bilayers helicities higher than 90% are observed for the three peptides, whereas in TFE:H 2 O solutions helical contents of only 53.7, 85.2 and 60.4% have been observed for ocellatin-LB1, -LB2, and -F1, respectively (Fig.…”

Thermodynamics of the binding of Substance P to lipid membranes

“…17,18 This model assumes that the peptide reacts with the surface of the vesicle consisting of lipids as in the following equation: nL+P↔PL n . In other words, it assumes that a peptide bonds with n lipid molecules on the vesicle surface.…”

pVEC hydrophobic N‐terminus is critical for antibacterial activity

“…AMPs may demonstrate multiple roles, but their main activity is bactericidal, killing bacteria by perturbing membrane permeability . Some CPPs also demonstrate AMP action by killing bacteria in infected mammalian cultures at doses that do not damage human cells …”

“…The uptake and membrane interaction mechanisms of some CPPs and AMPs have been examined using experimental methods for accurate representation of cellular environments and computational methods for atomistic details, but a clear description is still missing for pVEC . Peptide translocation takes place on the order of minutes, and in addition, the cellular and membrane environment is more complex than a simple membrane model.…”