This invention relates to macrostructures (and pharmaceutical formulations containing them) that include a parallel coiled-coil structure, wherein the parallel coiled-coil comprises a first coil of Formula I and a second coil of Formula II:

T1-f0-g0-a1-b1-c1-d1-e1-f1-g1-a2-b2-c2-d2-e2-f2-g2-a3-b3-c3-d3-e3-T2  (I)

T3-g′0-a′1-b′1-c′1-d′1-e′1-f′1-g′1-a′2-b′2-c′2-d′2-e′2-f′2-g′2-a′3-b′3-c′3-d′3-e′3-f′3-T4  (II),

as described in the present application. Methods of using these macrostructures are also disclosed.