Binding cavities of orange-G within fibers of the KLVFFA segment from Aβ.
Orange-G is bound internally to the steric zipper of KLVFFA (residues 16–21 of Aβ). It also contacts the lysine residues in the adjacent zipper. Peptide segments, forming β-sheet structures, are shown as arrows and sticks, colored by atom type with carbons in white. Orange-G carbons are in orange for one molecule and brown for the other molecule. Surface is shown for peptide atoms contacting the orange-G molecule with the orange carbons, shown as spheres. The view in (A) looks down the fiber axis. The view in (B) is perpendicular to the fiber axis. Only side chains of interacting residues are shown. The area of the fiber buried by orange-G (Methods) is 271 Å2 and 272 Å2 for the orange and brown colored orange-G, respectively, and is about 80% hydrophobic (contributed by the side chains of Leu17, Val18, Phe19, and Phe20). The polar interactions are contributed by the charged side chains of Lys16. In (B), one of the β-sheets from the adjacent pair and one orange-G molecule are removed for clarity.