Cross-linking of Wild-type and Mutant α2-Antiplasmins to Fibrin by Activated Factor XIII and by a Tissue Transglutaminase

• Published in: The Journal of biological chemistry 2000-12, Vol.275 (48), p.37382
• Main Authors: Kyung N. Lee, Chung S. Lee, Weon-Chan Tae, Kenneth W. Jackson, Victoria J. Christiansen, Patrick A. McKee
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M003375200

Human α 2 -antiplasmin (α 2 AP), the main inhibitor of plasmin-mediated fibrinolysis, is a substrate for plasma transglutaminase, also termed activated factor XIII (FXIIIa). Of 452 amino acids in α 2 AP, only Gln 2 is believed to be a fibrin-cross-linking (or FXIIIa-reactive) site. Kinetic efficiencies ( k cat / K m (app) ) of FXIIIa and the guinea pig liver tissue transglutaminase (tTG) and reactivities of Gln substrate sites were compared for recombinant wild-type α 2 AP (WT-α 2 AP) and Q2A mutant α 2 AP (Q2A-α 2 AP). [ 14 C]Methylamine incorporation showed the k cat / K m (app) of FXIIIa to be 3-fold greater than that of tTG for WT-α 2 AP. With FXIIIa or tTG catalysis, [ 14 C]methylamine was incorporated into Q2A-α 2 AP, indicating that WT-α 2 AP has more than one Gln cross-linking site. To identify transglutaminase-reactive sites in WT-α 2 AP or Q2A-α 2 AP, each was labeled with 5-(biotinamido)pentylamine by FXIIIa or tTG catalysis. After each labeled α 2 AP was digested by trypsin, sequence and mass analyses of each labeled peptide showed that 4 of 35 Gln residues were labeled with the following reactivities: Gln 2 > Gln 21 > Gln 419 > Gln 447 . Q 2 A-α 2 AP was also labeled at Gln 21 > Gln 419 > Gln 447 , but became cross-linked to fibrin by FXIIIa or tTG at approximately one-tenth the rate for WT-α 2 AP. These results show that α 2 AP is a better substrate for FXIIIa than for this particular tTG, but that either enzyme involves the same Gln substrate sites in α 2 AP and yields the same order of reactivities.