Fig. 4: Steric zipper morphology and β-sheet arrangements in amyloid-like APRs.

The interfaces of the hydrophobic zippers are indicated by the blue background and characterized by their respective contact area (Ų) and shape complementarity value (Sc). a APR^GLP1 assembled in antiparallel, equifacial β-sheets with steric zipper belonging to the class 7 amyloid-topology, creating a similar interface to that found in case of (b) Ac-EFIAWL. c The class 1 amyloid topology of APR^GLP2 results in two different interfaces (S1, S2). d Polymorph A of APR^ex-4. Antiparallel, equifacial β-sheets formed steric zippers of class 8 topology. e Polymorph B of APR^ex-4. Antiparallel and equifacial β-sheets form a mixed topology of class 7 and class 8. A lateral shift between adjacent β-sheets allows the formation of 3 different interfaces (S1, S2, and S3). While S1 and S3 are class 7 interfaces, S2 is of class 8 topology. f Polymorph A and (h) polymorph C of APR^Tc5b: Crystals formed in both acetonitrile/water and ethanol/water mixtures of almost identical packing morphology with different solvent molecules (acetonitrile or ethanol) occupying the same spots in the crystals that belong to class 8. As pairs of antiparallel β-sheets shift along the fibril axis, 4 or 6 H-bonds form between the shifted chains. g Polymorph B of APR^Tc5b: Antiparallel β-sheets are assembled in class 8 topology. In contrast to all other crystal structures presented here, none of the laterally shifted neighboring β-sheets run parallel to each other, resulting in the formation of different interfaces. i Polymorph D of APR^Tc5b: This polymorph contains β-strands in the parallel arrangement of class 1 topology.