(A) Top: schematics of 1/3-hexamer and 1/2-hexamer design. Two types of disulfide-bonds (S-S) are colored (A14C/E45C in blue, A42C/T54E in red). Bottom: SDS-PAGE demonstrating formation of 1/3- and 1/2-hexamers. On the left, CA samples run in reducing conditions show ~25 kDa monomers. On the right, CA samples run in non-reducing conditions reveal dimer, trimer, and hexamer species as designed. (B) Size-exclusion chromatography (SEC) demonstrates well-behaved partial-hexamer assemblies (marked with schematics). (C) Orthogonal views of the crystal structures (ribbon) of 1/3-hexamerEE (top) and 1/2-hexamerEE-ΔCTD (bottom) in the hexamer envelope (grey surface, PDB ID: 3H47). The structures are highly homologous to the corresponding portions in known hexamer crystal structures. See also Figure S2, Table S1, and Table S2.