Alzheimer's disease amyloid beta peptide 25-35 is localized in the membrane hydrocarbon core: X-ray diffraction analysis

Alzheimer's disease (AD) neuropathology is characterized by neuritic plaques composed primarily of amyloid beta peptide (A beta). An elevation in A beta in the cerebral cortex has been implicated in the pathophysiology of AD but its mechanism of action is unknown. The addition of A beta protein to neuronal cell cultures produces changes in the activity of various membrane proteins, including ion channels and receptors, potentially as a result of intercalating into the membrane bilayer. In this study, the interactions of the A beta fragment 25-35 [A beta(25-35)] with liposomes were directly examined by small angle x-ray diffraction approaches. One-dimensional electron density profiles generated from the diffraction data demonstrated that the addition of A beta(25-35) produced a discrete increase in electron density 0-12 Angstrom from the center of the lipid bilayer. Under these conditions, the membrane concentration of A beta(25-35) was 860-fold higher than in the aqueous buffer. These findings indicate that this peptide is highly lipophilic and inserts into the membrane hydrocarbon core. Following the intercalation of A beta(25-35) to this location in the membrane, the protein fragment may interact with regulatory membrane proteins. (C) 1996 Academic Press, Inc.