CB:Ag ratio of recombinant VWF mutants. Collagen-binding assays to (A) type I collagen and (B) type III collagen were performed in parallel with VWF:Ag ELISA. Error bars represent mean ± SD of 3 separate experiments performed in duplicate. Wild-type recombinant VWF and H1786A (a mutation previously shown to abolish collagen binding) are shown as controls. Only S1731T shows significant binding, which is greater with collagen type III. Coexpression of wild-type VWF with W1745C significantly improved binding to type III collagen.