The VASP TD structure. (A) Stereoview of VASP TD. Side chains forming the hydrophobic core are labeled, and the 15-residue repeat positions are marked in parentheses. (B) The hydrophobic core packing of VASP TD shown along the tetramer axis from the N-terminal side. Central core layers a, h, and l and the neighbor packing d/e layer are shown. (C) View of VASP TD showing residues that form intrahelical and interhelical salt bridges, together with the corresponding 2F_o – F_c electron-density map (contour level, 1.0 σ).

Schematic representation of the full-length VASP tetramer with bound ligands.

The 15-residue repeat pattern. (A) Amino acid sequence of VASP TD formatted to highlight the 15-residue repeat pattern. Hydrophobic residues most frequently found in the hydrophobic core of coiled coils (L, V, I, and M), as well as the Y and F residues, are highlighted in yellow. Acidic residues are shown in red, and basic residues are shown in blue. Residues that are not visible in the electron density are shown in italics. The assignment of the 15-residue repeat positions is shown beneath the amino acid sequence followed by the corresponding heptad positions as assigned by twister (19). Residues participating in the axial hydrophobic core are underlined. Residues in the d and e positions that form hydrophobic contacts between adjacent α-helices are underlined with a curvy line. (B) The sequence of residues 1,661–1,709 of the putative myosin-like protein (TrEMBL accession no. Q8ICM9) with apparent 15-residue repeats. (C) The sequence of residues 4–18 of the tetrabrachion fragment (8), forming a right-handed coiled-coil structure. (D) Helical net diagrams for the heptad, 11-residue, and 15-residue repeats. To make such a diagram, an imaginary piece of paper is wrapped around an α-helix. An arrow on the left side shows the direction of the helix from the N terminus to the C terminus. Positions forming the hydrophobic patch on the surface of the helix are marked by crosses with a dotted line showing the “middle line” of this patch. Color inserts show the ribbon diagrams of the GCN4-pLI leucine zipper (20) (PDB ID code 1GCL) with heptad repeats, the tetrabrachion protein (residues 19–52) (8) (PDB ID code 1FE6) with 11-residue repeats, and VASP TD.