Fig. 1: Structural, biochemical, and immunogenic analysis of E3 particles.

a Surface representations of E3 F-, EC-, and EE-particles and thin slices of the corresponding central sections viewed along the two-fold axes, respectively. The surface of the virus is colored by rainbow-color based on the distance of the viral elements from the center, starting with blue (closest) through green, yellow, and orange to red (farthest from the center). b Structure-based evolutionary relationship among the representative viruses from HEV-Bs: E18, echovirus 18; E3, echovirus 3; CVB1, coxsackievirus B1; E6, echovirus 6; E30, echovirus 30; CVB5, coxsackievirus B5; CVB3, coxsackievirus B3; E1, echovirus 1; CVA9, coxsackievirus A9; E11, echovirus 11. c Comparisons of the surface of E3 F-particle with those of other representative members of HEV-B (E18 (PDB: 6HBG), CVB3 (PDB: 4GB3), and CVA9 (PDB: 1D4M)). The color scheme is the same as in a. The “mesa” located at the top is marked using a black dotted square for each particle. d Structural details of the protomer (VP1: blue; VP2: green; VP3: red) of representative particles. The loops surrounding the canyon walls (VP1 BC loop, VP1 GH loop, and VP2 EF loop) and the loops surrounding the “mesa” structures are labeled in corresponding colors. e The binding affinities of E3 F-particle to 5G3 IgG estimated by SPR. f Neutralization of E3 by 5G3 using plaque-reduction neutralization test (PRNT). The Neut₅₀ value of 5G3 was 0.34 nM. g Surface representation of E3-5G3 complex. The viral capsid is colored the same as in a, and the 5G3 Fab is colored in cyan. h 5G3 Fab occupancy (left) and epitopes (right) located on viral pentamer. The pentamer is shown as surface (left) and cartoon (right), respectively. Residues comprising 5G3 epitope are shown as spheres. i The E3–5G3 binding interface. 5G3 are shown as cartoon, while E3 is shown as surface. The residues of the VP1 C-terminal (blue) insert into the 5G3 Fab hydrophobic pocket. The change of color reflects hydrophilic or hydrophobic nature of the residues, ranging from white (hydrophilic) to cyan (hydrophobic). Residues involved in the interactions between the virus (VP1: blue, VP3: red) and 5G3 are shown as sticks, and the hydrophobic interactions are shown as surface and colored in grey. Hydrogen bonds are marked as yellow dashes. j Clashes between 5G3 and two E3 receptors, CD55 (left)/FcRn (right). The pentamer, 5G3 light chain, 5G3 heavy chain, receptor CD55, and receptor FcRn are colored in grey, cyan, blue, magenta, and yellow, respectively.