Two-Dimensional IR Spectroscopy and Isotope Labeling Defines the Pathway of Amyloid Formation with Residue-Specific Resolution

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 16; pp. 6614 - 6619
• Main Authors: Shim, Sang-Hee, Gupta, Ruchi, Ling, Yun L., Strasfeld, David B., Raleigh, Daniel P., Zanni, Martin T., Hochstrasser, Robin M.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 21.04.2009; National Acad Sciences
• Subjects: Aggregation; Amino Acid Sequence; Amino Acids - metabolism; Amyloid - chemistry; Amyloid - metabolism; Amyloids; Biological Sciences; Cells; Complex Systems: From Chemistry to Systems Biology Special Feature; Humans; Infrared radiation; Infrared spectroscopy; Insulin resistance; Islet Amyloid Polypeptide; Isotope Labeling - methods; Isotopes; Isotopic labeling; Kinetics; Molecular Sequence Data; Molecular structure; Nucleation; Peptides; Physical Sciences; Protein Structure, Quaternary; Proteins; Reproducibility of Results; Solar fibrils; Spectrophotometry, Infrared; Spectrum analysis; Toxicity
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0805957106

There is considerable interest in uncovering the pathway of amyloid formation because the toxic properties of amyloid likely stems from prefibril intermediates and not the fully formed fibrils. Using a recently invented method of collecting 2-dimensional infrared spectra and site-specific isotope labeling, we have measured the development of secondary structures for 6 residues during the aggregation process of the 37-residue polypeptide associated with type 2 diabetes, the human islet amyloid polypeptide (hIAPP). By monitoring the kinetics at 6 different labeled sites, we find that the peptides initially develop well-ordered structure in the region of the chain that is close to the ordered loop of the fibrils, followed by formation of the 2 parallel β-sheets with the N-terminal β-sheet likely forming before the C-terminal sheet. This experimental approach provides a detailed view of the aggregation pathway of hIAPP fibril formation as well as a general methodology for studying other amyloid forming proteins without the use of structure-perturbing labels.