Influence of Trifluoroethanol on Membrane Interfacial Anchoring Interactions of Transmembrane α-Helical Peptides

Abstract

Interfacial anchoring interactions between aromatic amino acid residues and the lipid-water interface are believed to be important determinants for membrane protein structure and function. Thus, it is possible that molecules that partition into the lipid-water interface can influence membrane protein activity simply by interfering with these anchoring interactions. Here we tested this hypothesis by investigating the effects of 2,2,2-trifluoroethanol (TFE) on the interaction of a Trp-flanked synthetic transmembrane peptide (acetyl-GW(2)(LA)(8)LW(2)A-NH(2)) with model membranes of dimyristoylphosphatidylcholine. Two striking observations were made. First, using (2)H nuclear magnetic resonance on acyl chain deuterated lipids, we found that addition of 4 or 8 vol % of TFE completely abolishes the ability of the peptide to order and stretch the lipid acyl chains in these relatively thin bilayers. Second, we observed that addition of 8 vol % TFE reduces the tilt angle of the peptide from 5.3 degrees to 2.5 degrees, as measured by (2)H NMR on Ala-d(4) labeled peptides. The "straightening" of the peptide was accompanied by an increased exposure of Trp to the aqueous phase, as shown by Trp-fluorescence quenching experiments using acrylamide. The observation of a reduced tilt angle was surprising because we also found that TFE partioning results in a significant thinning of the membrane, which would increase the extent of hydrophobic mismatch. In contrast to the Trp-flanked peptide, no effect of TFE was observed on the interaction of a Lys-flanked analog (acetyl-GK(2)(LA)(8)LK(2)A-NH(2)) with the lipid bilayer. These results emphasize the importance of interfacial anchoring interactions for membrane organization and provide new insights into how molecules such as TFE that can act as anesthetics may affect the behavior of membrane proteins that are enriched in aromatic amino acids at the lipid-water interface.

Determining the Effects of Lipophilic Drugs on Membrane Structure by Solid-State NMR Spectroscopy: The Case of the Antioxidant Curcumin

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Rapeseed oil-rich diet alters in vitro menadione and nimesulide hepatic mitochondrial toxicity

“…induced by diet) may influence drug action at membrane protein targets. On the other hand, lipophilic drugs may influence membrane protein activity by interfering with bilayer biophysical properties, this mechanism contributing to their pharmacological effects and/or being responsible for unwanted nonspecific side effects (Adachi et al, 2007;Hwang et al, 2003;Lundbaek, 2008;Lundbaek et al, 2005;Özdirekcan et al, 2008). Disruption of lipid rafts, with redistribution of proteins between raft and non-raft domains, alterations of membrane curvature stress or bilayer thickness are some of the consequences of the incorporation of amphiphiles into the lipid bilayer with predictable repercussions in membrane protein activity (Szabo et al, 2007).…”

Probing the Lipid-Protein Interface Using Model Transmembrane Peptides with a Covalently Linked Acyl Chain

“…For q ¼ 0 , (3 cos 2 q À 1) equals unity (26). From the determined order parameters, we estimated the hydrocarbon thickness (D C ) of one monolayer as described previously (31,32).…”