PMC

Proposed packing of GNNQQNY β-strands (represented by arrows) in the unit cell of the microcrystals. The strands are extended and form parallel β-sheets. Each sheet packs against one neighboring sheet with its strands parallel to the first and one sheet with its strands antiparallel to the first. The registration of the sheets with one another along a and c is not yet known. The spacing between strands and sheets is ≈4.8 Å and ≈10 Å, respectively.

Powder x-ray diffraction intensities obtained from GNNQQNY microcrystals shown as a radial distribution. Vertical lines superimposed on the pattern indicate calculated reflection positions. Peaks in the resolution range 0 to 0.227 Å⁻¹ are labeled A–Z and those in the range 0.228 to 0.3 Å⁻¹ are labeled a–u. See Table 1, which is published with an enlarged version of this figure as supplemental material on the PNAS web site, www.pnas.org.

The Sup35 protein and constructs tested for crystallization. (a) Residues 1–123 make up the PrD or N region. Residues 124–253 are the highly charged M region, and residues 254–685 function in translation termination. (b) Sup35 constructs tested for crystallization. Δ22–69 indicates that residues 22–69, which confer the psi-no-more phenotype, have been deleted. Thx represents thioredoxin. (c) Peptidyl fragments from the Sup35 PrD. Underlined residues indicate non-native amino acid sequences. Superscripts give initial and final sequence positions. * indicate plasmids provided by Susan Lindquist.

Biophysical characterization of the Sup35 fragment GNNQQNY. (a) An electron micrograph of the GNNQQNY amyloid fibrils (Left) and x-ray diffraction pattern of partially aligned fibrils (Right). The meridional reflections at 4.7 Å and equatorial reflections at 10 Å are characteristic of the cross-β structure of amyloid. (b) Effect of Sup 35 on GNNQQNY turbidity. GNNQQNY aggregation was monitored in the presence (upper curve) and absence (middle curve) of Sup35. The turbidity of Sup35 alone also is shown (lower curve). (c) An electron micograph of the GNNQQNY microcrystals (Left) and their x-ray diffraction pattern (Right). An aggregate of these microcrystals diffracts x-rays to 0.9-Å resolution. The darkest ring in the powder pattern is the 4.7-Å reflection.