ABSTRACT
The interaction of the intrinsically disordered polypeptide islet amyloid polypeptide (IAPP), which is associated with type 2 diabetes (T2D), with the Alzheimer's disease amyloid-ß (Aß) peptide modulates their self-assembly into amyloid fibrils and may link the pathogeneses of these two cell-degenerative diseases. However, the molecular determinants of this interaction remain elusive. Using a systematic alanine scan approach, fluorescence spectroscopy, and other biophysical methods, including heterocomplex pulldown assays, far-UV CD spectroscopy, the thioflavin T binding assay, transmission EM, and molecular dynamics simulations, here we identified single aromatic/hydrophobic residues within the amyloid core IAPP region as hot spots or key residues of its cross-interaction with Aß40(42) peptide. Importantly, we also find that none of these residues in isolation plays a key role in IAPP self-assembly, whereas simultaneous substitution of four aromatic/hydrophobic residues with Ala dramatically impairs both IAPP self-assembly and hetero-assembly with Aß40(42). Furthermore, our experiments yielded several novel IAPP analogs, whose sequences are highly similar to that of IAPP but have distinct amyloid self- or cross-interaction potentials. The identified similarities and major differences controlling IAPP cross-peptide interaction with Aß40(42) versus its amyloid self-assembly offer a molecular basis for understanding the underlying mechanisms. We propose that these insights will aid in designing intervention strategies and novel IAPP analogs for the management of type 2 diabetes, Alzheimer's disease, or other diseases related to IAPP dysfunction or cross-amyloid interactions.
Subject(s)
Amino Acids/metabolism , Amyloid beta-Peptides/metabolism , Islet Amyloid Polypeptide/metabolism , Models, Molecular , Peptide Fragments/metabolism , Protein Aggregation, Pathological/metabolism , Amino Acid Substitution , Amino Acids/chemistry , Amino Acids, Aromatic , Amyloid beta-Peptides/chemical synthesis , Amyloid beta-Peptides/chemistry , Circular Dichroism , Humans , Hydrophobic and Hydrophilic Interactions , Islet Amyloid Polypeptide/chemical synthesis , Islet Amyloid Polypeptide/chemistry , Kinetics , Methylation , Microscopy, Electron, Transmission , Molecular Dynamics Simulation , Peptide Fragments/chemical synthesis , Peptide Fragments/chemistry , Protein Stability , Protein Structure, Secondary , Solid-Phase Synthesis Techniques , Solubility , Spectrometry, FluorescenceABSTRACT
The design of inhibitors of protein-protein interactions mediating amyloid self-assembly is a major challenge mainly due to the dynamic nature of the involved structures and interfaces. Interactions of amyloidogenic polypeptides with other proteins are important modulators of self-assembly. Here we present a hot-segment-linking approach to design a series of mimics of the IAPP cross-amyloid interaction surface with Aß (ISMs) as nanomolar inhibitors of amyloidogenesis and cytotoxicity of Aß, IAPP, or both polypeptides. The nature of the linker determines ISM structure and inhibitory function including both potency and target selectivity. Importantly, ISMs effectively suppress both self- and cross-seeded IAPP self-assembly. Our results provide a novel class of highly potent peptide leads for targeting protein aggregation in Alzheimer's disease, type 2 diabetes, or both diseases and a chemical approach to inhibit amyloid self-assembly and pathogenic interactions of other proteins as well.
