FIG 1.

Synthesis and purification of VNA2-Tcd. (A) Schematic diagram of TcdA and TcdB toxins, respectively. GTD, enzymatic glucosyltransferase domain; TMD, transmembrane domain; RBD, receptor binding domain. AH3 and AA6 bind in the GTD region and the TMD region of TcdA, respectively, and 5D and E3 bind to different regions of the GTD in TcdB. (B) Diagram of the heterotetramer VNA2-Tcd, which was synthetically generated and contains two potent neutralizing VHHs to each toxin. The protein contains a thioredoxin protein at the amino end, followed by four VHHs separated by a flexible spacer peptide with a carboxyl-terminal E-tag peptide and an albumin-binding peptide to increase serum persistence.