FIGURE 5.

Starting structures and interaction interfaces for tetrameric ΔN6-β₂m. A, ΔN6-β₂m monomer was reconstructed from the domain-swapped dimer x-ray crystal structure (PDB ID 2X89) by extracting the coordinates manually and subsequently rebuilding a missing loop using MODELLER. B, the reconstructed monomer shows striking similarity with the monomeric ΔN6-β₂m structure determined by NMR (PDB ID 2XKU). Colored regions show the corresponding β-sheets A to G in the two structures. C, model structure of ΔN6-β₂m tetramer reveals that intradimeric interfaces are formed by the interaction of the domain-swapped hinge regions and on the opposite side, the D strands interact through hydrogen bonding between Glu-50 and Ser-52. The interdimeric interface is formed from the interaction of the domain-swapped hinge regions by hydrogen bonding of Ser-88 (chain D), Thr-86, and Ser-88 (chain C) with Thr-86 (chain B), Ser-88, and Gln-89 (chain A). Hydrogen bonds were identified using the HBonds tool in VMD (visual molecular dynamics).