Fig. 1.
Modeling zipper electrostatic tail–tail interactions. (A) Structural model of zipper tail domain (1111–1968) based on a highly regular coiled-coil (the trigger site of the actin crosslinker cortexillin I; Burkhard et al., 2000; PDB ID: 1D7M). Skip residues were removed to keep the heptad repeat in register (see Materials and Methods). Electrostatic potential mapping onto the structure reveals the relative concentration of negative and positive charge along the tail. The scale ranges from -19 (red) to 19 (blue) KbT/ec. (B) Electrostatic interaction energy of two assembly domains (1849–1940) in parallel and antiparallel orientations. These calculations were performed using Coulomb’s law as implemented in Advanced Poisson–Boltzman Solver. Interaction energy is the difference in energy of a particular configuration compared to two isolated tail domains. Asterisks mark the configurations shown in the following panel. (C) Structural models of stable binary assembly domain interactions in parallel and antiparallel orientations. The assembly domain is marked with a black bar. Note that the electrostatic surface maps were calculated for isolated assembly domains. (D) Electrostatic interaction energy of two tail fragments (1744–1968) in parallel and antiparallel orientations. In addition to the wild-type sequence, interaction energies for 4D (basic residues 1880, 1883, 1887, and 1890 mutated to aspartic acid) and 3K (acidic residues 1780, 1781, and 1784 mutated to lysine) mutations are shown. Asterisks mark the configurations shown in the following panel. (E) Structural models of the most stable, binary tail fragment interactions for the 1744–1968 fragment in parallel and antiparallel orientations. Note that the electrostatic surface maps were calculated for isolated assembly domains.