The role of aromatic side-chains in amyloid growth and membrane interaction of the islet amyloid polypeptide fragment LANFLVH |
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Authors: | Danilo Milardi Michele F M Sciacca Matteo Pappalardo Domenico M Grasso Carmelo La Rosa |
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Institution: | (1) Istituto di Biostrutture e Bioimmagini, U.O.S. Catania, Consiglio Nazionale delle Ricerche, Viale Andrea Doria 6, 95125 Catania, Italy;(2) Dipartimento di Scienze Chimiche, Universita’ di Catania, Viale Andrea Doria 6, 95125 Catania, Italy; |
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Abstract: | Human islet amyloid polypeptide (hIAPP) is known to misfold and aggregate into amyloid deposits that may be found in pancreatic
tissues of patients affected by type 2 diabetes. Recent studies have shown that the highly amyloidogenic peptide LANFLVH,
corresponding the N-terminal 12–18 region of IAPP, does not induce membrane damage. Here we assess the role played by the
aromatic residue Phe in driving both amyloid formation and membrane interaction of LANFLVH. To this aim, a set of variant
heptapeptides in which the aromatic residue Phe has been substituted with a Leu and Ala is studied. Differential scanning
calorimetry (DSC) and membrane-leakage experiments demonstrated that Phe substitution noticeably affects the peptide-induced
changes in the thermotropic properties of the lipid bilayer but not its membrane damaging potential. Atomic force microscopy
(AFM), ThT fluorescence and Congo red birefringence assays evidenced that the Phe residue is not required for fibrillogenesis,
but it can influence the self-assembling kinetics. Molecular dynamics simulations have paralleled the outcome of the experimental
trials also providing informative details about the structure of the different peptide assemblies. These results support a
general theory suggesting that aromatic residues, although capable of affecting the self-assembly kinetics of small peptides
and peptide-membrane interactions, are not essential either for amyloid formation or membrane leakage, and indicate that other
factors such as β-sheet propensity, size and hydrophobicity of the side chain act synergistically to determine peptide properties. |
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