jp056697y_si_001.pdf (133.21 kB)
Interaction of the Neurotransmitter, Neuropeptide Y, with Phospholipid Membranes: Film Balance and Fluorescence Microscopy Studies†
journal contribution
posted on 2006-11-09, 00:00 authored by Martina Dyck, Mathias LöscheThe 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) versus 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 πi = 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 suggest 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 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.