Figure 3.

The gpN capsid protein. (A) Ribbon diagram of gpN_B (the most complete subunit), colored by structural feature: N-arm, red; E-loop, pink; P-domain β-sheet, blue; P-domain α-helices, yellow (α3 is the spine helix); A-domain, green. The right-hand panel is rotated by 180°. Key structural features are labeled, and the gpO cleavage site between residues 31 and 32 is indicated (circle). (B) Intra-capsomer interaction between the gpN_B (yellow) and gpN_D (blue) subunits, showing how the gpN_B E-loop overlays the spine helix of the neighboring (gpN_D) subunit. The right-hand panel is rotated by 180° and shows how the gpN_B N-arm and α0 grasp the P-domain of gpN_D from underneath. (C) Electrostatic surfaces for the gpN_B and gpN_D subunits from panel B, separated and rotated by 120° in opposite directions, as indicated by the insets. Interaction surfaces of opposite charge are indicated by the dashed lines. (D) Inter-capsomeric interaction between three gpN_D and their neighboring gpN_B subunits related by the icosahedral threefold axis. The insets show details of the interactions between the gpN_D and gpN_B subunits.