Mechanistic Studies of Peptide Self-Assembly: Transient α-Helices to Stable β-Sheets

The pathologic self-assembly of proteins is associated with typically late-onset disorders such as Alzheimer’s disease, Parkinson’s disease, and type 2 diabetes. Important mechanistic details of the self-assembly are unknown, but there is increasing evidence supporting the role of transient α-helice...

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Published inJournal of the American Chemical Society Vol. 132; no. 51; pp. 18223 - 18232
Main Authors Liu, Gai, Prabhakar, Anabathula, Aucoin, Darryl, Simon, Miranda, Sparks, Samuel, Robbins, Kevin J, Sheen, Andrew, Petty, Sarah A, Lazo, Noel D
Format Journal Article
LanguageEnglish
Published WASHINGTON American Chemical Society 29.12.2010
Amer Chemical Soc
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Summary:The pathologic self-assembly of proteins is associated with typically late-onset disorders such as Alzheimer’s disease, Parkinson’s disease, and type 2 diabetes. Important mechanistic details of the self-assembly are unknown, but there is increasing evidence supporting the role of transient α-helices in the early events. Islet amyloid polypeptide (IAPP) is a 37-residue polypeptide that self-assembles into aggregates that are toxic to the insulin-producing β cells. To elucidate early events in the self-assembly of IAPP, we used limited proteolysis to identify an exposed and flexible region in IAPP monomer. This region includes position 20 where a serine-to-glycine substitution (S20G) is associated with enhanced formation of amyloid fibrils and early onset type 2 diabetes. To perform detailed biophysical studies of the exposed and flexible region, we synthesized three peptides including IAPP(11-25)WT (wild type), IAPP(11-25)S20G, and IAPP(11-25)S20P. Solution-state NMR shows that all three peptides transiently populate the α-helical conformational space, but the S20P peptide, which does not self-assemble, transiently samples a broken helix. Under similar sample conditions, the WT and S20G peptides populate the α-helical intermediate state and β-sheet end state, respectively, of fibril formation. Our results suggest a mechanism for self-assembly that includes the stabilization of transient α-helices through the formation of NMR-invisible helical intermediates followed by an α-helix to β-sheet conformational rearrangement. Furthermore, our results suggest that reducing intermolecular helix−helix contacts as in the S20P peptide is an attractive strategy for the design of blockers of peptide self-assembly.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja1069882