Figure 2: Geometrical assembly of γPFD filaments.

(a) Two-way connectors were designed by fusion of two TERM monomers. Each connector is designed to impart a specific angle between filaments. (b) Filaments of γPFD elongate from the connector in two directions, (c) at a specific angle imparted by the orientation of the TERM X1 β-sheet interfaces of the connector. (d) TEM image of two-way connectors assembled with γPFD to create self-closing structures either (e) ovoidal or (f) figure-eight in shape (scale bars, 100 nm). (g) A three-way connector was created by fusion of TERM with the foldon trimerization domain. (h) A trimer of TERM-foldon that (i) assembles with γPFD to elongate outwards from the TERM β-sheet interfaces to create a pinwheel structure. (j) TEM of the three-way connector assembled with three γPFD filaments into a pinwheel shape with arms of uniform length and (k) its structure confirmed by the positioning of a gold nanoparticle (arrow) covalently attached to a C-terminal cysteine on the connector (scale bars, 50 nm). (l) Cross-linking of filaments using a high stoichiometric ratio of three-way connector to γPFD (scale bar, 200 nm).