Figure 6.

Interactions at the Δ19ω₂···Δ19ω₂ interface (A) between helices α1′ and α1 of subunits A′ and B of [Δ19ω₂]₂-(→→), (see Figure 2A). The Δ19ω₂ are related by a pseudo-2-fold axis perpendicular to the paper plane (red ellipse). Residues with contacts <4 Å to neighbor helix are depicted with side-chains, colors as in Figure 2. Bifurcated hydrogen bonds between His38 (His38′) and Ala45O/Lys46O to Ala45′O/Lys46′O of the other subunit in dashed lines. (B) Superimposition as in Figure 2B with view on the dimer–dimer interface to show that dimer–dimer interactions are comparable in both structures.