Neutron reflectometry studies define prion protein N-terminal peptide membrane binding

Area of Science:

• Biochemistry
• Biophysics
• Neuroscience

Background:

• Prion protein (PrP) misfolding causes transmissible spongiform encephalopathies.
• PrP undergoes posttranslational modifications, including cleavage into N1 and N2 fragments.
• N1 and N2 fragments interact with negatively charged phospholipids at low pH.

Purpose of the Study:

• To refine binding parameters of N1 and N2 fragments with lipid bilayers.
• To structurally define the interaction of N1 and N2 fragments with lipid bilayers.
• To investigate the impact of N1 and N2 binding on lipid membrane structure.

Main Methods:

• Neutron reflectometry to determine structural details of peptide-lipid interactions.
• Quartz crystal microbalance interrogation to quantify binding.
• Analysis of peptide insertion depth and effect on lipid acyl tails.

Main Results:

• N1 and N2 peptides insert into the interstitial space between phospholipid headgroups.
• Peptides do not penetrate the acyl tail region of the lipid bilayer.
• N1 fragment exhibits stronger binding than N2 fragment.
• Lipid acyl tails lengthen, and lipid area decreases, indicating increased lipid order.

Conclusions:

• N-terminal prion protein fragments interact with lipid bilayers by inserting between headgroups.
• The interaction induces increased lipid order without phase transition.
• These findings contrast with Ab and ?-synuclein interactions and suggest a functional role for N-terminal fragment-membrane interactions.