Fig. 1.

Computer renderings of the Perutz et al. (5) structure of poly Q. (A) Space-filling model of one subunit of 42 Q residues with two turns of β-strands, showing the central pore, here tilted, that is perpendicular to the plane of the membrane. Note the outer convolutions of the surface of the subunit, by the outward-facing Q residues. These might serve to make gear-like associations between β-amyloid subunits in the plane of the membrane; others might serve as regions of attachment of specific integral membrane proteins to the membrane-interior regions of the poly Q amyloid, such as we propose in the text. Red balls are O atoms, and blue ones are N atoms. (B) Stick model of two stacked subunits of poly Q, each subunit containing 42 Q residues, one subunit rendered in dark blue, the other in light blue. (C) Stick model of a short segment of one subunit (enlarged) that faces a region of bonding between one turn and another of the subunit, showing the hydrogen bonds (strings of dots) formed between backbone (red) and (dark blue) groups. (D) Stick model of a small segment of one subunit, showing (by strings of dots) the hydrogen bonds formed by (i) inter-β-strand bonds between the backbone groups, (the O in red and the N in dark blue) and (ii) of the alternate Q residues extending from one or the other surface of the two-turn helix sheet. This view is parallel to the axis that runs down the pore of the subunit, and perpendicular to the plane of the membrane bilayer.