Structure of the FMDV-AWH-W2 complex and key determinations on VP3 of FMDV serotype A.

(A) Cartoon representation of one protomer showing the interaction interface between W2 scFv and the capsid. The heavy chain and light chain of W2 are colored sky blue and rose madder, 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 B-B knob, CD loop (C), βC, EF/GH loops (B), BC loop (D) on VP3. 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) Amino acid sequence alignment of 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 W2 against wildtype (A/WH/CHA/09) and mutants corresponding to interactive residues (VP3 D59A, VP3 Q71A, VP3 K76A, VP3 K84A, VP3 T131A, VP3 T132A and VP3 T178A) 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.