An amyloid-forming peptide from the yeast prion Sup35 reveals a dehydrated beta-sheet structure for amyloid.
X-ray diffraction and other biophysical tools reveal features of the atomic structure of an amyloid-like crystal. Sup35, a prion-like protein in yeast, forms fibrillar amyloid assemblies intrinsic to its prion function. We have identified a polar peptide from the N-terminal prion-determining domain of Sup35 that exhibits the amyloid properties of full-length Sup35, including cooperative kinetics of aggregation, fibril formation, binding of the dye Congo red, and the characteristic cross-beta x-ray diffraction pattern. Microcrystals of this peptide also share the principal properties of the fibrillar amyloid, including a highly stable, beta-sheet-rich structure and the binding of Congo red. The x-ray powder pattern of the microcrystals, extending to 0.9-A resolution, yields the unit cell dimensions of the well-ordered structure. These dimensions restrict possible atomic models of this amyloid-like structure and demonstrate that it forms packed, parallel-stranded beta-sheets. The unusually high density of the crystals shows that the packed beta-sheets are dehydrated, despite the polar character of the side chains. These results suggest that amyloid is a highly intermolecularly bonded, dehydrated array of densely packed beta-sheets. This dry beta-sheet could form as Sup35 partially unfolds to expose the peptide, permitting it to hydrogen-bond to the same peptide of other Sup35 molecules. The implication is that amyloid-forming units may be short segments of proteins, exposed for interactions by partial unfolding.
University of California-Department of Energy Laboratory of Structural Biology and Molecular Medicine, Department of Chemistry and Biochemistry, Box 951570, University of California, Los Angeles, CA 90095-1570, USA.
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Balbirnie
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Grothe
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Eisenberg
D000595:Amino Acid Sequence; D000682:Amyloid / Q000737:chemistry*; D001483:Base Sequence; D003460:Crystallization; D018360:Crystallography, X-Ray; D017931:DNA Primers; D005656:Fungal Proteins / Q000737:chemistry*; D008854:Microscopy, Electron; D010454:Peptide Termination Factors; D011328:Prions / Q000737:chemistry*; D011487:Protein Conformation; D029701:Saccharomyces cerevisiae Proteins; D017550:Spectroscopy, Fourier Transform Infrared
D000682:Amyloid; D017931:DNA Primers; D005656:Fungal Proteins; D010454:Peptide Termination Factors; D011328:Prions; C068068:SUP35 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins