Surface behaviour and peptide-lipid interactions of the antibiotic peptides, Maculatin and Citropin

Copyright © 2004 Elsevier B.V. All rights reserved.Surface behaviour of Maculatin 1.1 and Citropin 1.1 antibiotic peptides have been studied using the Langmuir monolayer technique in order to understand the peptide-membrane interaction proposed as critical for cellular lysis. Both peptides have a spontaneous adsorption at the air-water interface, reaching surface potentials similar to those obtained by direct spreading. Collapse pressures (Pi(c), stability to lateral compression), molecular areas at maximal packing and surface potentials (DeltaV) obtained from compression isotherms of both pure peptide monolayers are characteristic of peptides adopting mainly alpha-helical structure at the interface. The stability of Maculatin monolayers depended on the subphase and increased when pH was raised. In an alkaline environment, Maculatin exhibits a molecular reorganization showing a reproducible discontinuity in the Pi-A compression isotherm. Both peptides in lipid films with the zwitterionic palmitoyl-oleoyl-phosphatidylcholine (POPC) showed an immiscible behaviour at all lipid-peptide proportions studied. By contrast, in films with the anionic palmitoyl-oleoyl-phosphatidylglycerol (POPG), the peptides showed miscible behaviour when the peptides represented less than 50% of total surface area. Additional penetration experiments also demonstrated that both peptides better interact with POPG compared with POPC monolayers. This lipid preference is discussed as a possible explanation of their antibiotic properties.Ernesto E. Ambroggio, Frances Separovic, John Bowie and Gerardo D. Fideliohttp://www.elsevier.com/wps/find/journaldescription.cws_home/601272/description#descriptio

Aβ Amyloid Fibers Drastically Alter the Topography and Mechanical Properties of Lipid Membranes

Alzheimer's disease (AD) is related to the fibrillation of the Aβ peptides at neuronal membranes, a process that depends on the lipid composition and may impart different physical states to the membrane. In the present work, we study the properties of the Aβ peptide when mixed with a zwitterionic lipid (DMPC), using the Langmuir monolayer technique as an approach to control membrane physical conditions. First, we build on previous characterizations of pure Aβ monolayers and observe that, in addition to high shear, these films present a pronounced compressional hysteresis. When Aβ is assembled with DMPC in a binary film, the resulting membranes become heterogeneous, with a peptide-enriched phase distributed in a network-like pattern, and they exhibit a lateral transition that depends on the Aβ content. At lower peptide proportions, the films segregate into two well-defined phases: one consisting of lipids and another enriched with peptides. The reflectivity of these phases differs from that obtained for pure Aβ films. Thus, the formed fibers effectively cover most of the interface area and remain stable at higher pressures (from 20 to 30 mN m-1 depending on Aβ content) compared to pure peptide films (17 mN m-1). Furthermore, such structures induce a compressional hysteresis in the film, similar to that of pure peptide films (which is nonexistent in the pure lipid monolayer), even at low peptide proportions. We claim that the mechanical properties at the interface are governed by the size of the fibril-like structures. Based on the low molar fractions and surface packing at which these phenomena were observed, we postulate that as a consequence of peptide intermolecular interactions, Aβ may have drastic effects on the molecular arrangement and mechanical properties of a lipid membrane.</p

Differential Interaction of Antimicrobial Peptides with Lipid Structures Studied by Coarse-Grained Molecular Dynamics Simulations

In this work; we investigated the differential interaction of amphiphilic antimicrobial peptides with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid structures by means of extensive molecular dynamics simulations. By using a coarse-grained (CG) model within the MARTINI force field; we simulated the peptide–lipid system from three different initial configurations: (a) peptides in water in the presence of a pre-equilibrated lipid bilayer; (b) peptides inside the hydrophobic core of the membrane; and (c) random configurations that allow self-assembled molecular structures. This last approach allowed us to sample the structural space of the systems and consider cooperative effects. The peptides used in our simulations are aurein 1.2 and maculatin 1.1; two well-known antimicrobial peptides from the Australian tree frogs; and molecules that present different membrane-perturbing behaviors. Our results showed differential behaviors for each type of peptide seen in a different organization that could guide a molecular interpretation of the experimental data. While both peptides are capable of forming membrane aggregates; the aurein 1.2 ones have a pore-like structure and exhibit a higher level of organization than those conformed by maculatin 1.1. Furthermore; maculatin 1.1 has a strong tendency to form clusters and induce curvature at low peptide–lipid ratios. The exploration of the possible lipid–peptide structures; as the one carried out here; could be a good tool for recognizing specific configurations that should be further studied with more sophisticated methodologies

Superactivity and conformational changes on alpha-chymotrypsin upon interfacial binding to cationic micelles.

The catalytic behaviour of alpha-CT (alpha-chymotrypsin) is affected by cationic micelles of CTABr (hexadecyltrimethylammonium bromide). The enzyme-micelle interaction leads to an increase in both the V(max) and the affinity for the substrate p -nitrophenyl acetate, indicating higher catalytic efficiency for bound alpha-CT. The bell-shaped profile of alpha-CT activity with increasing CTABr concentrations suggests that the micelle-bound enzyme reacts with the free substrate. Although more active with CTABr micelles, the enzyme stability is essentially the same as observed in buffer only. Enzyme activation is accompanied by changes in alpha-CT conformation. Changes in tertiary structure were observed by the increase in intensity and the red shift in the alpha-CT tryptophan fluorescence spectrum, suggesting the annulment of internal quenching and a more polar location of tryptophan residues. Near-UV CD also indicated the transfer of aromatic residues to a more flexible environment. CTABr micelles also induces an increase in alpha-helix, as seen by far-UV CD and FTIR (Fourier-transform infrared) spectroscopies. The far-UV CD spectrum of alpha-CT shows an increase in the intensity of the positive band at 198 nm and in the negative band at 222 nm, indicating an increased alpha-helical content. This is in agreement with FTIR studies, where an increase in the band at 1655 cm(-1), corresponding to the alpha-helix, was shown by fitting analysis and difference spectroscopy. Spectral deconvolution indicated a reduction in the beta-sheet content in micelle-bound alpha-CT. Our data suggest that the higher catalytic efficiency of micelle-bound alpha-CT results from significant conformational changes