Figure 5.

Cell-surface–binding activity of the CROP domains from both TcdA and TcdB. Vero cells were incubated in A with TcdA (3 nm) and TcdA CROP (15 nm, 30 nm) and in B with TcdB (0.8 nm) and TcdB CROP (16 nm, 80 nm), and surface-bound proteins were subjected to immunoblot analysis by an anti-TcdA and anti-TcdB antibody, respectively. C, inhibition of TcdA cytotoxicity at a fixed concentration by the A-CROP domain in molar excess was measured by SRB assay. D, inhibition of TcdB cytotoxicity at a fixed concentration by the B-CROP domain in molar excess was measured by SRB assay.