Ion Mobility-Mass Spectrometry Reveals a Dipeptide That Acts as a Molecular Chaperone for Amyloid β

Previously, we discovered and structurally characterized a complex between amyloid beta 140 and the neuropeptide leucine enkephalin. This work identified leucine enkephalin as a potentially useful starting point for the discovery of peptide-related biotherapeutics for Alzheimers disease. In order to better understand such complexes that are formed in vitro, we describe here the analysis of a series of site-directed amino acid substitution variants of both peptides, covering the leucine enkephalin sequence in its entirety and a large number of selected residues of amyloid beta 140 (residues: D1, E3, F4, R5, H6, Y10, E11, H13, H14, Q15, K16, E22, K28, and V40). Ion mobility-mass spectrometry measurements and molecular dynamics simulations reveal that the hydrophobic C-terminus of leucine enkephalin (Phe-Leu, FL) is crucial for the formation of peptide complexes. As such, we explore here the interaction of the dipeptide FL with both wildtype and variant forms of amyloid beta in order to structurally characterize the complexes formed. We find that FL binds preferentially to amyloid beta oligomers and attaches to amyloid beta within the region between its N-terminus and its hydrophobic core, most specifically at residues Y10 and Q15. We further show that FL is able to prevent fibril formation.