Fig. 4. Domain-2 structure.

a Ramachandran plot for Domain-2 of V-Csn apo1. The main chain torsion angles (phi and psi) are shown as light blue triangles (glycine), light blue squares (proline) and blue circles (all other residues). The three favored regions for β-sheets, α-helices and left-handed helices are colored pink. The additionally allowed regions are colored pale yellow. b Hydrogen bonding interactions between the two short β-strands, β4 and β5, in Domain-2. c Hydrogen bonding interactions in the 20-residue region in Domain-2 between helix α1 (a 3₁₀ helix) and strand β5 (shown as gray sticks for main chain atoms only). This region contains four residues designated as β-bridges, G56, W63, V68 and P74 (colored magenta). These residues are involved in main chain-main chain hydrogen bonds with other β-bridge residues and residues adjacent to them. The 20-residue region is folded into two hairpin loops, with an acidic residue (D57 and D69) in each loop stabilizing each hairpin through hydrogen bonding interactions with main chain amide nitrogen atoms. d Superposition of the predicted AlphaFold V-Csn structure (gray ribbon) and the V-Csn apo1 crystal structure (green and pink ribbons representing Domain-1 and Domain-2, respectively).