Site-Specific Hydration Status of an Amphipathic Peptide in AOT Reverse Micelles

Abstract

Reverse micelles formed by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in isooctane (IO) and water have long been used as a means to provide a confined aqueous environment for various applications. In particular, AOT reverse micelles have often been used as a template to mimic membrane-water interfaces. While earlier studies have shown that membrane-binding peptides can indeed be incorporated into the polar cavity of AOT reverse micelles where they mostly fold into an alpha-helical structure, the underlying interactions leading to the ordered conformation are however not well understood. Herein, we have used circular dichroism (CD) and infrared (IR) spectroscopies in conjunction with a local IR marker (i.e., the CN group of a non-natural amino acid, p-cyano-phenylalanine) and a global IR reporter (i.e., the amide I' band of the peptide backbone) to probe the conformation as well as the hydration status of an antimicrobial peptide, mastoparan x (MPx), in AOT reverse micelles of different water contents. Our results show that at, w0=6, MPx adopts an alpha-helical conformation with both the backbone and hydrophobic side chains mostly dehydrated, whereas its backbone becomes partially hydrated at w0=20. In addition, our results suggest that the amphipathic alpha-helix so formed orients itself in such a manner that its positively charged, lysine-rich, hydrophilic face points toward the negatively charged AOT head groups, while its hydrophobic face is directed toward the polar interior of the water pool. This picture is in marked contrast to that observed for the binding of MPx to phospholipid bilayers wherein the hydrophobic surface of the bound alpha-helix is buried deeper into the membrane interior.

Structure and Immunogenicity of a Peptide Vaccine, Including the Complete HIV-1 gp41 2F5 Epitope

“…6A, left). This finding is consistent with the comparable structures adopted by membrane-binding peptides at interfaces of reverse micelles and membranes (71). In sharp contrast, the amide-I band measured in the POPGMPERp samples was narrower, suggestive of higher conformational order, and corresponded almost exclusively to ␣-helical conformers (Fig.…”

Simulations of the confinement of ubiquitin in self-assembled reverse micelles

“…29 Experiments in RM are conducted with different solvents. 14,17,18 However, to maintain consistency in the force field and with previous simulations, 26,29,32,33 we use iso-octane as the organic solvent. Simulations are conducted with the parallel molecular dynamics program NAMD.…”

“…Pocket-U and pocket-V are named due to the shape of pocket region. The hydration of Pocket-V has been studied by Denisov et al, 59,60 and water in this pocket is responsible for the 17 O relaxation dispersion. The lifetime for a long-lived buried water molecule in ubiquitin has been estimated to be 60-90 ns.…”

“…16 The size of RMs depends on the water to surfactant ratio, w 0 , which can be well controlled to alter the confinement and hydration level. 17 Depending on the choice of surfactant, the protein may not maintain the folded structure when encapsulated in a RM. angel@rpi.edu.…”

A theoretical forecast of the hydrogen bond changes in the electronic excited state for BN and its derivatives

“…BN and some of its derivatives have received great attention as ideal probes of the local environment. The hydrogen-bonding interactions between the nitrile groups and the protic solvents are of considerable interest since the vibration of the nitrile group is basically decoupled from the other part of the molecule and is sensitive to the formation of the hydrogen bond [51][52][53][54][55][56][57][58]. The CN vibration of BN affected by the hydrogen bonding environments was investigated by Aschaffenburg et al [59].…”