Exploring the Biophysical Interaction of 3-Pentadecylphenol with Head Group Region of Lipid Membrane using Fisetin as an Interfacial Membrane Probe

3-Pentadecylphenol (PDP) is a phenolic lipid easily available from natural sources. This compound has different pharmacological, biological and industrial applications. A molecular level understanding on the membrane modification properties of...

Lipid phase dependent distinct emission behaviour of hydrophobic carbon dots: C-dots based membrane probe

We observe an unique distinct emission behaviour of hydrophobic carbon dots (H-CDs) embedded within the ordered and the disordered phase of the lipid membrane. The H-CDs exhibit the blue emission...

Melittin Induces Local Order Changes in Artificial and Biological Membranes as Revealed by Spectral Analysis of Laurdan Fluorescence

Antimicrobial peptides (AMPs) are a class of molecules widely used in applications on eukaryotic and prokaryotic cells. Independent of the peptide target, all of them need to first pass or interact with the plasma membrane of the cells. In order to have a better image of the peptide action mechanism with respect to the particular features of the membrane it is necessary to better understand the changes induced by AMPs in the membranes. Laurdan, a lipid membrane probe sensitive to polarity changes in the environment, is used in this study for assessing changes induced by melittin, a well-known peptide, both in model and natural lipid membranes. More importantly, we showed that generalized polarization (GP) values are not always efficient or sufficient to properly characterize the changes in the membrane. We proved that a better method to investigate these changes is to use the previously described log-normal deconvolution allowing us to infer other parameters: the difference between the relative areas of elementary peak (ΔSr), and the ratio of elementary peaks areas (Rs). Melittin induced a slight decrease in local membrane fluidity in homogeneous lipid membranes. The addition of cholesterol stabilizes the membrane more in the presence of melittin. An opposite response was observed in the case of heterogeneous lipid membranes in cells, the local order of lipids being diminished. RS proved to be the most sensitive parameter characterizing the local membrane order, allowing us to distinguish among the responses to melittin of both classes of membrane we investigated (liposomes and cellular membranes). Molecular simulation of the melittin pore in homogeneous lipid bilayer suggests that lipids are more closely packed in the proximity of the melittin pore (a smaller area per lipid), supporting the experimental observation.

The orientation of a membrane probe from structural analysis by enhanced Raman scattering

ABSTRACTSmall fluorescent molecules are widely used as probes of biomembranes. Different probes optically indicate membrane properties such as the lipid phase, thickness, viscosity, and electrical potential. The detailed molecular mechanisms behind probe signals are not well understood, in part due to the lack of tools to determine probe position and orientation in the membrane. Optical measurements on aligned biomembranes and lipid bilayers provide some degree of orientational information based on anisotropy in absorption, fluorescence, or nonlinear optical properties. These methods typically find the polar tilt angle between the membrane normal and the long axis of the molecule. Here we show that solution-phase surface enhanced Raman scattering (SERS) spectra of lipid membranes on gold nanorods can be used to determine molecular orientation of molecules within the membrane. The voltage sensitive dye 4-(2-(6-(dibutylamino)-2-naphthalenyl)ethenyl)-1-(3-sulfopropyl)-hydroxide, known as di-4-ANEPPS, is studied. Through the analysis of several peaks in the SERS spectrum, the polar angle from the membrane normal is found to be 63°, and the roll angle around the long axis of the molecule to be 305° from the original orientation. This structural analysis method could help elucidate the meaning of fluorescent membrane probe signals, and how they are affected by different lipid compositions.