Figure 4.

GCN4-pVe and GCN4-pVg Associate to Form an Antiparallel, Four-Stranded Coiled Coil

(A) Lateral view of the antiparallel heterotetramer (residues 2–31). The C^α backbones of GCN4-pVe (magenta) and GCN4-pVg (blue) are depicted. Red van der Waals surfaces identify residues at the a positions, and green van der Waals surfaces identify residues at the d positions.

(B) Axial view of the antiparallel heterotetramer. The view is from the N termini of helices A and B, looking down the superhelical axis. The van der Waals surfaces are colored red for Val10(a) of helices A and B and green for Leu27(d) of helices C and D.

(C) The interhelical hydrogen-bonding network formed by a Mg²⁺ ion, structured waters, and the c and f residues of helices B and C. The Mg²⁺ ion is represented as a purple ball; water molecules are represented as small, red spheres; and hydrogen bonds are represented by dotted lines.

(D) A portion of the 2F_o − F_c electron density map (contoured at 1.5σ) showing the coordination geometry of the Mg²⁺ ion (purple ball) connecting the helices B and C. Water molecules are shown as red spheres, and magnesium coordinations are denoted by dotted lines.

(E) Helical wheel representation of the antiparallel heterotetramer. Heptad positions are labeled a–g.