Identification of Factor‐XIIIa‐Reactive Glutaminyl Residues in the Propolypeptide of Bovine von Willebrand Factor

von Willebrand factor is a large multimeric plasma protein which plays important roles in platelet aggregation, blood coagulation and probably also in the adhesion of endothelial cells. A 100‐kDa propeptide, called the propolypeptide of von Willebrand factor (pp‐vWF), is generated during biosynthesis. We found that pp‐vWF served as a substrate for transglutaminases including human factor XIIIa and guinea pig liver transglutaminase [Usui, T., Takagi, J. & Saito, Y. (1993) J. Biol. Chem. 268, 12311–123161. As such, it could form cross‐linked copolymers with the extracellular matrix protein, laminin, making it all the more likely that pp‐vWF plays a role in cell adhesion phenomena [Takagi, J., Sudo, Y., Saito, T. & Saito, Y. (1994) Eur. J. Biochem. 222, 861–867]. In this work, we identified the Gln residues in pp‐vWF specifically reacting with blood coagulation factor XIIIa as amine acceptors. The fluorescent amine, dansylcadaverine, was employed for labeling the enzyme‐reactive sites of the protein. Following partial proteolysis, fragments containing the labeled Gln residues were isolated by passage through an anti‐dansyl affinity chromatographic column. Amino acid sequence analyses of the fragments revealed that, out of about 40 Gln residues in pp‐vWF, only four could be modified in the factor‐XIIIa‐catalyzed reaction.