Interaction of the Neurotransmitter, Neuropeptide Y, with Phospholipid Membranes:  Film Balance and Fluorescence Microscopy Studies

Abstract

The association of neuropeptide Y (NPY) with air/water interfaces and with phospholipid monolayers on water subphases and on physiological buffer has been investigated. Surface pressure (π) vs. molecular area (A) relations of the peptide at water surfaces depend on the concentration of the spreading solutions. Independent of that concentration, they show a transition from a low-density state to a high-density state at π ∼ 12 mN/m. Similar features are observed in the NPY adsorption to preformed monolayers (Δπ(t→∞) as a function of π i = π(t=0) where t = 0 signifies the time of peptide injection). The transition is also observed in cospread lipid/NPY monolayers and is interpreted as the exclusion of the peptide from the surface layer. The reproducibility of the isotherms after expansion suggests that cospread lipid/peptide monolayers are thermodynamically stable and that the peptide remains associated with the monolayer after exclusion from the lipid surface.A comparison of NPY association with zwitterionic and with anionic lipids, as well as a comparison of the interactions on pure water and on physiological buffer, suggests that electrostatic attraction plays a major role in the energetics of peptide binding to the membrane surface. Dual label fluorescence microscopy demonstrates that the peptide associates preferentially with the disordered liquid-condensed (LC) monolayer phase and also suggests that it self-aggregates upon exceeding a critical surface concentration. A NPY variant with a distorted α-helix interacts with the surface as strongly as the natural NPY but expands the monolayers more. This suggests that the helix motif in the peptide is more important for the interaction with the receptor than for binding of the peptide to the membrane surface. In context, these observations attribute a specific role to the membrane in funneling the signal peptide to its membrane receptor.

Controlling Molecular Recognition with Lipid/Polymer Domains in Vesicle Membranes

“…As reported in the literature, the lipid dye Rh-DHPE (l exc = 561 nm) is largely excluded from ordered phases in mono-and bilayer membranes (e.g., liquid condensed phases [15,17] ). In Figure 2 B, Rh-DHPE is preferentially incorporated into the polymer-enriched phase (compare with Figure 2 A) which indicates a less-ordered phase state, whereas the black patches in Figure 2 A,B consist of a moreordered DPPC-enriched phase.…”

Interaction of the Neurotransmitter, Neuropeptide Y, with Phospholipid Membranes: Infrared Spectroscopic Characterization at the Air/Water Interface

“…1 The surface thermodynamics of NPY shows that the peptide interacts strongly with lipid monolayers and suggested that this interaction is similar with zwitterionic and with anionic lipids. 4 As we look into the molecular details with IRRAS, however, it becomes clear in this work that the peptide interacts substantially stronger with DMPS − than with DPPC. Among other implications, this may provide for a mechanism which facilitates receptor binding once the transmitter encounters the receptor in the trajectory of its 2D random walk along the membrane surface.…”

“…Among other implications, this may provide for a mechanism which facilitates receptor binding once the transmitter encounters the receptor in the trajectory of its 2D random walk along the membrane surface. 4 The IRRAS results presented here help to characterize the underlying interactions in molecular detail and to provide more definite answers regarding the association of the peptide with the biomimetic model surfaces.…”

Structural investigation on the adsorption of the MARCKS peptide on anionic lipid monolayers – effects beyond electrostatic

“…Surface pressure-area isotherms of the monolayers were obtained using a thermostated Langmuir film balance of home made design (Dyck and Lösche, 2006) at a subphase temperature of 20 • C. The studies of the mesoscopic morphology of the monolayer were performed with a Zeiss Axiotech Vario epifluorescence microscope (dye NBD C 12 -HPC, Molecular Probes, Leiden, The Netherlands), associated with the film balance (Krüger et al, 1999) The dissolved DPPC and the DPPC/DPPS mixtures were spread on the subphase and the solvent was allowed to evaporate for at least 10 min. The monolayers were compressed typically at a barrier speed that corresponded to approximately 2 Å 2 /(molecule min) and the surface pressure was monitored continuously.…”