Two-dimensional infrared spectroscopy reveals the complex behaviour of an amyloid fibril inhibitor


Amyloid formation has been implicated in the pathology of over 20 human diseases, but the rational design of amyloid inhibitors is hampered by a lack of structural information about amyloid–inhibitor complexes. We use isotope labelling and two-dimensional infrared spectroscopy to obtain a residue-specific structure for the complex of human amylin (the peptide responsible for islet amyloid formation in type 2 diabetes) with a known inhibitor (rat amylin). Based on its sequence, rat amylin should block formation of the C-terminal β-sheet, but at 8 h after mixing, rat amylin blocks the N-terminal β-sheet instead. At 24 h after mixing, rat amylin blocks neither β-sheet and forms its own β-sheet, most probably on the outside of the human fibrils. This is striking, because rat amylin is natively disordered and not previously known to form amyloid β-sheets. The results show that even seemingly intuitive inhibitors may function by unforeseen and complex structural processes.

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Figure 1: Sequence of human and rat amylin and structural model of human amylin fibrils.
Figure 2: Rat amylin prevents human amylin from forming N-terminal, and not C-terminal, β-sheets at 8 h after mixing.
Figure 3: Human amylin β-sheets, initially disrupted by rat amylin, eventually form and promote the formation of rat amylin β-sheets.
Figure 4: Electron microscopy supports the unexpected structural dynamics revealed by 2D IR results.
Figure 5: Molecular dynamics simulation suggests that the N-terminals of human and rat amylin can form a partially ordered β-sheet complex.


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Support for this research was provided by the National Institutes of Health (grants DK79895 to M.T.Z., GM078114 to D.P.R. and DK088184 to J.J.d.P.) and the National Science Foundation (CRC grant CHE 0832584 to M.T.Z and D.P.R.). The authors are grateful to R. Tycko for providing the coordinates for his structural model of human amylin fibrils.

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C.T.M., D.P.R. and M.T.Z. designed the research. C.T.M. performed the 2D IR and electron microscopy measurements. P.M., A.W.M. and P.C. synthesized and purified peptides. P.M and P.C performed the thioflavin-T fluorescence measurements. C.C., S.S. and J.J.d.P. designed and performed the molecular dynamics simulations. C.T.M. and M.T.Z. analysed data. C.T.M., D.P.R. and M.T.Z. wrote the manuscript and coordinated contributions by other authors.

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Correspondence to Martin T. Zanni.

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Middleton, C., Marek, P., Cao, P. et al. Two-dimensional infrared spectroscopy reveals the complex behaviour of an amyloid fibril inhibitor. Nature Chem 4, 355–360 (2012).

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