Matching Effects in the Interaction of Ionic Surfactants with Fluorescent Reagents in Micellar Solutions of Triton X-100

The influence of cationic and anionic surfactant solutions on the character of the fluorescence spectra of reagents of different charge and hydrophobicity in aqueous solutions of nonionic surfactant Triton X-100 has been studied. An increase in the fluorescence intensity and a shift in the position of the fluorescence maximum with increasing hydrophobicity of reagents and ionic surfactants have been shown. The analytical signal of the surfactant is further amplified in the proximity of the charge values of the reagent and the counterion of the surfactant. The non-monotonic nature of the hydrophobicity effect of cationic surfactants on their analytical signal in the system has been shown. The observed effects are explained by the realization of charge and hydrophobic matching in the interaction of surfactants with the fluorescent reagents. The obtained effects are significant in the design of fluorescent systems for the determination and study of surfactant micelles. Conditions for detecting the content of cetylpyridinium chloride by reaction with eosin Y and sodium tetradecyl sulfate by reaction with rhodamine 6G in the presence of Triton X-100 were proposed. The methods have been tested in detecting the content of the ionic surfactants in pharmaceuticals.

PIP2 promotes conformation-specific dimerization of the EphA2 membrane region

The impact of the EphA2 receptor on cancer malignancy hinges on the two different ways it can be activated. EphA2 induces anti-oncogenic signaling after ligand binding, but ligand-independent activation of EphA2 is pro-oncogenic. It is believed that the transmembrane (TM) domain of EphA2 adopts two alternate conformations in the ligand-dependent and the ligand-independent states. However, it is poorly understood how the difference in TM helical crossing angles found in the two conformations impacts the activity and regulation of EphA2. We devised a method that uses hydrophobic matching to stabilize two conformations of a peptide comprising the EphA2 TM domain and a portion of the intracellular juxtamembrane (JM) segment. The two conformations exhibit different TM crossing angles, resembling the ligand-dependent and ligand-independent states. We developed a single-molecule technique using SMALPs to measure dimerization in membranes. We observed that the signaling lipid PIP2 promotes TM dimerization, but only in the small crossing angle state, which we propose corresponds to the ligand-independent conformation. In this state the two TM are almost parallel, and the positively charged JM segments are expected to be close to each other, causing electrostatic repulsion. The mechanism PIP2 uses to promote dimerization might involve alleviating this repulsion due to its high density of negative charges. Our data reveal a conformational coupling between the TM and JM regions, and suggest that PIP2 might directly exert a regulatory effect on EphA2 activation in cells that is specific to the ligand-independent conformation of the receptor.

PIP2 promotes conformation-specific dimerization of the EphA2 membrane region

The impact of the EphA2 receptor on cancer malignancy hinges on the two different ways it can be activated. EphA2 induces anti-oncogenic signaling after ligand binding, but ligand-independent activation of EphA2 is pro-oncogenic. It is believed that the transmembrane (TM) domain of EphA2 adopts two alternate conformations in the ligand-dependent and the ligand-independent states. However, it is poorly understood how the difference in TM helical crossing angles found in the two conformations impacts the activity and regulation of EphA2. We devised a method that uses hydrophobic matching to stabilize two conformations of a peptide comprising the EphA2 TM domain and a portion of the intracellular juxtamembrane (JM) segment. The two conformations exhibit different TM crossing angles, resembling the ligand-dependent and ligand-independent states. We developed a single-molecule technique using SMALPs to measure dimerization in membranes. We observed that the signaling lipid PIP2 promotes TM dimerization, but only in the small crossing angle state, which we propose corresponds to the ligand-independent conformation. In this state the two TM are almost parallel, and the positively charged JM segments are expected to be close to each other, causing electrostatic repulsion. The mechanism PIP2 uses to promote dimerization might involve alleviating this repulsion due to its high density of negative charges. Our data reveal a conformational coupling between the TM and JM regions, and suggest that PIP2 might directly exert a regulatory effect on EphA2 activation in cells that is specific to the ligand-independent conformation of the receptor.

Influence of the sterol aliphatic side chain on membrane properties: a molecular dynamics study

Cholesterol provides best hydrophobic matching, induces maximal membrane ordering, and displays highest preference for saturated phospholipid acyl chains, among a homologous ser ies of sterols with side chains of varying lengths.

Interaction of NBD-labelled fatty amines with liquid-ordered membranes: a combined molecular dynamics simulation and fluorescence spectroscopy study

The NBD fluorophore of NBD-Cnis located more externally in liquid-ordered membranes. Perfect hydrophobic matching is met for myristic and palmitic chains.