Fig 4.

CPB sequence variation effects on host cell cytotoxicity and toxin binding. (A) CPB cytotoxicity for HUVEC cells was determined after a 3-h treatment using an MTT cell viability assay for both CPB variants. The mean amounts of CPB found to be necessary for causing 50% cytotoxicity from four replicate experiments are presented. (B) The ability of both CPB variants to bind to and oligomerize on HUVEC cells was assayed. Relative amounts of CPB binding/oligomerization were determined by Western blotting and densitometry. The mean results of four independent assays are presented. (C) A representative Western blot of the host cell binding is shown. Note the absence of any free (monomeric) CPB on these gels. #, there was a significant (P < 0.05) difference between the results for CPB variants. Error bars indicate standard errors of the means.