Modulation of Interfacial Hydration by Carbonyl Groups in Lipid Membranes

Study of the Membrane Activity of the Synthetic Peptide ∆M3 Against Extended-Spectrum β-lactamase Escherichia coli Isolates

Escherichia coli is the most common microorganism causing nosocomial or community-acquired bacteremia, and extended-spectrum β-lactamase-producing Escherichia coli isolates are identified worldwide with increasing frequency. For this reason, it is necessary to evaluate potential new molecules like antimicrobial peptides. They are recognized for their biological potential which makes them promising candidates in the fight against infections. The goal of this research was to evaluate the potential of the synthetic peptide ΔM3 on several extended-spectrum β-lactamase producing E. coli isolates. The antimicrobial and cytotoxic activity of the peptide was spectrophotometrically determined. Additionally, the capacity of the peptide to interact with the bacterial membrane was monitored by fluorescence microscopy and infrared spectroscopy. The results demonstrated that the synthetic peptide is active against Escherichia coli isolates at concentrations similar to Meropenem. On the other hand, no cytotoxic effect was observed in HaCaT keratinocyte cells even at 10 times the minimal inhibitory concentration. Microscopy results showed a permeabilizing effect of the peptide on the bacteria. The infrared results showed that ΔM3 showed affinity for the lipids of the microorganism's membrane. The results suggest that the ∆M3 interacts with the negatively charged lipids from the E. coli by a disturbing effect on membrane. Finally, the secondary structure experiments of the peptide showed a random structure in solution that did not change during the interaction with the membranes.

Water as a Link between Membrane and Colloidal Theories for Cells

This review is an attempt to incorporate water as a structural and thermodynamic component of biomembranes. With this purpose, the consideration of the membrane interphase as a bidimensional hydrated polar head group solution, coupled to the hydrocarbon region allows for the reconciliation of two theories on cells in dispute today: one considering the membrane as an essential part in terms of compartmentalization, and another in which lipid membranes are not necessary and cells can be treated as a colloidal system. The criterium followed is to describe the membrane state as an open, non-autonomous and responsive system using the approach of Thermodynamic of Irreversible Processes. The concept of an open/non-autonomous membrane system allows for the visualization of the interrelationship between metabolic events and membrane polymorphic changes. Therefore, the Association Induction Hypothesis (AIH) and lipid properties interplay should consider hydration in terms of free energy modulated by water activity and surface (lateral) pressure. Water in restricted regions at the lipid interphase has thermodynamic properties that explain the role of H-bonding networks in the propagation of events between membrane and cytoplasm that appears to be relevant in the context of crowded systems.

Thermally Driven Transformation of Water Clustering Structures at Self-Assembled Monolayers

Water clustering structures are considered to play key roles in various temperature-dependent life activities. However, our fundamental understanding of the temperature-dependent water structures remains murky because of the limits of the real-time and real-condition monitoring techniques at the molecular level. We propose an in situ ATR-IR approach combining Gaussian fitting to qualitatively and quantitatively explore the temperature-dependent structural stability and transformation of the three water components, multimer water (MW), intermediate water (IW), and network water (NW), on interfaces with different wettabilities. Our results show that the transformation between NW and IW/MW will occur with a change in temperature. This conversion process shows reversibility on hydrophilic Au NPs film/ZnSe, while it is irreversible on a hydrophobic mercaptohexane self-assembled monolayer due to the irreversibility of the monolayer structure and the hydrophobic confinement effect. The established approach enables us to explore the change in the water properties at any interfaces upon external stimuli.

Breakdown of classical paradigms in relation to membrane structure and functions

Updates of the mosaic fluid membrane model implicitly sustain the paradigms that bilayers are closed systems conserving a state of fluidity and behaving as a dielectric slab. All of them are a consequence of disregarding water as part of the membrane structure and its essential role in the thermodynamics and kinetics of membrane response to bioeffectors. A correlation of the thermodynamic properties with the structural features of water makes possible to introduce the lipid membrane as a responsive structure due to the relaxation of water rearrangements in the kinetics of bioeffectors' interactions. This analysis concludes that the lipid membranes are open systems and, according to thermodynamic of irreversible formalism, bilayers and monolayers can be reasonable compared under controlled conditions. The inclusion of water in the complex structure makes feasible to reconsider the concept of dielectric slab and fluidity.

Effect of cholesterol on the hydration properties of ester and ether lipid membrane interphases

Fluorescence spectroscopy and Molecular Dynamics results show that cholesterol reduces water along the chains in ether lipids by changing the water distribution pattern between tightly and loosely bound water molecules. Water distribution was followed by emission spectra and generalized polarization of 6-dodecanoyl-2-dimethyl aminonaphthalene (Laurdan) inserted in 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (14: 0 Diether PC) membranes. Molecular Dynamics simulations indicate that the action of cholesterol could be different in ether PC in comparison to ester PC. In addition, Cholesterol seems to act "per se" as an additional hydration center in ether lipids. Regardless of the phase state, cholesterol both in DMPC and 14:0 Diether PC vesicles, changed the distribution of water molecules decreasing the dipole relaxation of the lipid interphase generating an increase in the non-relaxable population. Above 10% Cholesterol/14:0 Diether PC ratio vesicles' interphase present an environment around Laurdan molecules similar to that corresponding to ester PC.

Interaction of chlorogenic acid with model lipid membranes and its influence on antiradical activity

Chlorogenic acid (CGA) is a strong phenolic antioxidant with antibacterial properties composed by a caffeoyl ester of quinic acid. Although a number of benefits has been reported and related to interactions with the red blood cell membranes, details on its membrane action and how composition and membrane state may affect it, is not yet well defined. In this work, the interaction of CGA with lipid monolayers and bilayers composed by 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC); 1,2-di-O-tetradecyl-sn-glycero-3-phosphocholine (14:0 diether PC); 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-di-O-hexadecyl-sn-glycero-3-phosphocholine (16:0 diether PC) were studied at different surface pressures (π). The kinetics of interaction was found to be more rapid in DMPC than in the absence of carbonyl groups. Measurements by FTIR-ATR at different water activities confirm specific interactions of CGA with carbonyl and phosphate groups affecting water level along hydrocarbon region. The antioxidant activity of CGA in the presence of DMPC unilamellar vesicles, evidenced by the absorbance reduction of the radical cation ABTS^•+, is significantly different with respect to aqueous solution. The influence of CGA on antiradical activity (ARA) with lipid membranes depending on the hydration state of the lipid interface is discussed.