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Designed peptides that assemble into cross-α amyloid-like structures


Amyloids adopt ‘cross-β’ structures composed of long, twisted fibrils with β-strands running perpendicular to the fibril axis. Recently, a toxic peptide was proposed to form amyloid-like cross-α structures in solution, with a planar bilayer-like assembly observed in the crystal structure. Here we crystallographically characterize designed peptides that assemble into spiraling cross-α amyloid-like structures, which resemble twisted β-amyloid fibrils. The peptides form helical dimers, stabilized by packing of small and apolar residues, and the dimers further assemble into cross-α amyloid-like fibrils with superhelical pitches ranging from 170 Å to 200 Å. When a small residue that appeared critical for packing was converted to leucine, it resulted in structural rearrangement to a helical polymer. Fluorescently tagged versions of the designed peptides form puncta in mammalian cells, which recover from photobleaching with markedly different kinetics. These structural folds could be potentially useful for directing in vivo protein assemblies with predetermined spacing and stabilities.

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We thank D. Bulkley, P. Jin, S. Li, X. Liu, N. Polizzi, N. Schmidt and H. Wu for technical help. This work was primarily supported by NIH grant R35GM122603 to W.F.D., with additional support from the NSF (CHE1413295) for the MRSEC program to the LRSM at the University of Pennsylvania. H.T.K. was supported by a Ruth L. Kirschstein NRSA Postdoctoral Fellowship (F32GM125217). Y.L. was supported by a Howard Hughes Medical Institute-Helen Hay Whitney Foundation Postdoctoral Fellowship.

Author information

S.-Q.Z. and W.F.D. conceived the project. S.-Q.Z. designed all the peptide sequences and performed in vitro experiments with H.T.K., M.L. and Y.L. H.H. and J.Y. conducted cellular in vivo experiments. L.L. solved and refined all the crystal structures. S.-Q.Z., H.H, J.Y., H.T.K., Y.L., X.S., L.L. and W.F.D. analyzed the data. S.-Q.Z. and W.F.D. prepared the manuscript with contributions from all the authors.

Correspondence to Xiaokun Shu or Lijun Liu or William F. DeGrado.

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The authors declare no competing interests.

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Further reading

Fig. 1: The amyloid-like structure of αAmmem.
Fig. 2: Design of cross-α amyloid-like assembly.
Fig. 3: The aggregation behavior and fibril formation of the water-soluble peptides and the crystal structures of the cross-α amyloid-like fibrils.
Fig. 4: Packing of αAmL as a helical polymer composed of helix tetramers and its configurational relationship with the cross-α amyloid-like assembly of αAmG and αAmS.
Fig. 5: EGFP-tagged αAm peptides form inclusions in the cytosol of mammalian cells; αAmG, αAmA and αAmS form a solid-like phase, whereas αAmL is more mobile.