Structure of the FMDV-AWH-W125 complex and key determinations on VP2 as well as VP3 of FMDV serotype A.

(A) Cartoon representation of one protomer showing the interaction interface between W125 scFv and the capsid. The heavy chain and light chain of W125 are colored purple and orange, respectively. The capsid proteins VP1 to VP4 are colored blue, green, red and yellow, respectively. (B to D) Expanded views of the interaction interface highlighting the Ββ, E-F loop (B), B-C loop and H-I loop (C) of VP2 as well as B-B knob and H-I loop (D) of VP3 within one protomer. Presumable hydrogen bonds and salt bridges in the interaction interface are marked by black dashed lines. (E) Identification of rescued single-substitution mutants by immunofluorescence analysis. BHK-21 cells were infected with rescue mutants at an MOI of 10 for 4 h. FMDV protein 3A was detected using mouse mAb 3A24 and an Alexa Fluor 561-conjugated secondary antibody. (F) Sequence alignment of VP2/VP3 of A/AF72, A/WH/CHA/09 and A/GDMM/2013 strains. The critical residues in interactive interfaces are indicated with black triangles. (G) The neutralization efficacy of W125 against wildtype (A/WH/CHA/09) and mutants corresponding to interactive residues (VP2 D68A, VP2 T70A, VP2 T71A, VP2 H77A, VP2 E131A, VP2 Q196A, VP3 K61A and VP3 Q197A) was evaluated using a microneutralization assay. The neutralization concentration represents the lowest antibody required to fully prevent CPE. * indicates a significant difference compared to wildtype at P<0.05. ** indicates a significant difference compared to wildtype at P<0.01. NS indicates no significant difference.