The Bacteriostatic Activity of 2-Phenylethanol Derivatives Correlates with Membrane Binding Affinity.

The hydrophobic tails of aliphatic primary alcohols do insert into the hydrophobic core of a lipid bilayer. Thereby, they disrupt hydrophobic interactions between the lipid molecules, resulting in a decreased lipid order, i.e., an increased membrane fluidity. While aromatic alcohols, such as 2-phenylethanol, also insert into lipid bilayers and disturb the membrane organization, the impact of aromatic alcohols on the structure of biological membranes, as well as the potential physiological implication of membrane incorporation has only been studied to a limited extent. Although diverse targets are discussed to be causing the bacteriostatic and bactericidal activity of 2-phenylethanol, it is clear that 2-phenylethanol severely affects the structure of biomembranes, which has been linked to its bacteriostatic activity. Yet, in fungi some 2-phenylethanol derivatives are also produced, some of which appear to also have bacteriostatic activities. We showed that the 2-phenylethanol derivatives phenylacetic acid, phenyllactic acid, and methyl phenylacetate, but not Tyrosol, were fully incorporated into model membranes and affected the membrane organization. Furthermore, we observed that the propensity of the herein-analyzed molecules to partition into biomembranes positively correlated with their respective bacteriostatic activity, which clearly linked the bacteriotoxic activity of the substances to biomembranes.

Lipid Bilayer Interactions of Peptidic Supramolecular Polymers and Their Impact on Membrane Permeability and Stability.

The synthesis and physicochemical characterization of supramolecular polymers with tunable assembly profiles offer exciting opportunities, involving the development of new biomedical carriers. Because synthetic nanocarriers aim to transport substances across or toward cellular membranes, we evaluated the interactions of amphiphilic peptide-based supramolecular polymers with lipid bilayers. Here, we focused on nanorod-like supramolecular polymers, obtained from two C3-symmetric dendritic peptide amphiphiles with alternating Phe/His sequences, equipped with a peripheral tetraethylene glycol dendron (C3-PH) or charged ethylenediamine end groups (C3-PH+). Triggered by pH changes, these amphiphiles assemble reversibly. Our results show that the supramolecular polymers have an impact on the lipid order in model membranes. Changes in the lipid order were observed depending on the charge state of the amphiphilic building blocks, as well as the chemical composition and physical properties of the bilayer. Furthermore, we further performed cell viability assays with the C3-PH+ and C3-PH supramolecular polymers. For C3-PH, the cell viability and extent of proliferation were decreased and the membrane permeability was enhanced, indicating a strong interaction of the polymer with cellular membranes. The results have implications for the design of novel pH-switchable supramolecular drug carriers and delivery vehicles that can respond to an altered microenvironment of tumorous or inflamed tissue.

Lipid Binding Controls Dimerization of the Coat Protein p24 Transmembrane Helix.

Coat protein (COP) I and COP II complexes are involved in the transport of proteins between the endoplasmic reticulum and the Golgi apparatus in eukaryotic cells. The formation of COP I/II complexes at membrane surfaces is an early step in vesicle formation and is mastered by p24, a type I transmembrane protein. Oligomerization of p24 monomers was suggested to be mediated and/or stabilized via interactions within the transmembrane domain, and the p24 transmembrane helix appears to selectively bind a single sphingomyelin C18:0 molecule. Furthermore, a potential cholesterol-binding sequence has also been predicted in the p24 transmembrane domain. Thus, sphingomyelin and/or cholesterol binding to the transmembrane domain might directly control the oligomeric state of p24 and, thus, COP vesicle formation. In this study, we show that sequence-specific dimerization of the p24 transmembrane helix is mediated by a LQ7 motif, with Gln187 being of special importance. Whereas cholesterol has no direct impact on p24 dimerization, binding of the sphingolipid can clearly control dimerization of p24 in rigid membrane regions. We suggest that specific binding of a sphingolipid to the p24 transmembrane helix affects p24 dimerization in membranes with increased cholesterol contents. A clearly defined p24 dimerization propensity likely is crucial for the p24 activity, which involves shuttling in between the endoplasmic reticulum and the Golgi membrane, in which cholesterol and SM C18:0 concentrations differ.

Against Expectations: Unassisted RNA Adsorption onto Negatively Charged Lipid Bilayers.

The composition and physicochemical properties of biological membranes can be altered by diverse membrane integral and peripheral proteins as well as by small molecules, natural and synthetic. Diverse oligonucleotides have been shown to electrostatically interact with cationic and bivalent ion loaded zwitterionic liposomes, leading to the formation of oligonucleotide-liposome aggregates. However, interaction of RNAs with other membrane surfaces remains ill understood. We used the nonnatural RNA10 to investigate RNA binding to anionic and net-uncharged membrane surfaces. RNA10 had initially been selected in a screen for nonnatural RNA motives that bind to phosphatidylcholine liposomes in the presence of Mg2+. Here we show that interaction of defined RNA molecules with membrane surfaces crucially depends on electrostatic surface properties. Furthermore, RNA10 electrostatically binds to anionic lipid bilayers in the absence of Mg2+ or other bivalent cations, and this interaction leads to measurably changed physicochemical properties of the bilayer and the oligonucleotide. Thus, the structure of polyanionic RNA can be modulated via contact with negatively charged membrane surfaces and vice versa.

Nitrated Fatty Acids Modulate the Physical Properties of Model Membranes and the Structure of Transmembrane Proteins.

Nitrated fatty acids (NO2 -FAs) act as anti-inflammatory signal mediators, albeit the molecular mechanisms behind NO2 -FAs' influence on diverse metabolic and signaling pathways in inflamed tissues are essentially elusive. Here, we combine fluorescence measurements with surface-specific sum frequency generation vibrational spectroscopy and coarse-grained computer simulations to demonstrate that NO2 -FAs alter lipid organization by accumulation at the membrane-water interface. As the function of membrane proteins strongly depends on both, protein structure as well as membrane properties, we consecutively follow the structural dynamics of an integral membrane protein in presence of NO2 -FAs. Based on our results, we suggest a molecular mechanism of the NO2 -FA in vivo activity: Driven by the NO2 -FA-induced lipid layer reorganization, the structure and function of membrane-associated (signaling) proteins is indirectly affected.