Cross-linking of wild-type and mutant alpha 2-antiplasmins to fibrin by activated factor XIII and by a tissue transglutaminase.
Human alpha(2)-antiplasmin (alpha(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 alpha(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 alpha(2)AP (WT-alpha(2)AP) and Q2A mutant alpha(2)AP (Q2A-alpha(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-alpha(2)AP. With FXIIIa or tTG catalysis, [(14)C]methylamine was incorporated into Q2A-alpha(2)AP, indicating that WT-alpha(2)AP has more than one Gln cross-linking site. To identify transglutaminase-reactive sites in WT-alpha(2)AP or Q2A-alpha(2)AP, each was labeled with 5-(biotinamido)pentylamine by FXIIIa or tTG catalysis. After each labeled alpha(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-alpha(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-alpha(2)AP. These results show that alpha(2)AP is a better substrate for FXIIIa than for this particular tTG, but that either enzyme involves the same Gln substrate sites in alpha(2)AP and yields the same order of reactivities.
Lee
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William K. Warren Medical Research Institute and the Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73190, USA. kyung-lee@ouhsc.edu
Lee
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Tae
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Jackson
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Christiansen
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McKee
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D001483:Base Sequence; D002384:Catalysis; D017931:DNA Primers; D005337:Fibrin / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011503:Transglutaminases / Q000378:metabolism*; D000979:alpha-2-Antiplasmin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D017931:DNA Primers; D011994:Recombinant Proteins; D000979:alpha-2-Antiplasmin; D005337:Fibrin; D011503:Transglutaminases