FIG 1.

V_HHs 7F and E3 bind to the GTD of TcdB. (A and B) V_HHs 7F and E3 were tested for specific binding to both TcdA and TcdB by ELISA. Toxin-coated 96-well plates were incubated with serial dilutions of 7F or E3. Goat anti-E tag-IgG-HRP was used as a secondary antibody. Overall binding was determined by absorbance at 450 nm (optical density at 450 nm [OD₄₅₀]). (C) 7F and E3 binding to TcdB by Western blotting. Specific 7F, E3, monoclonal antibody recognizing the C-terminal portion of TcdB (MoAb), or alpaca polyserum binding to holotoxin TcdB (polyclonal Abs) were assessed by immunoblotting. The bands represent full-length TcdB (∼270 kDa), the C-terminal fragment of cleaved TcdB (aa 544 to 2366, ∼ 207 kDa), and the cleaved GTD (aa 1 to 543, ∼63 kDa).