title: Why alpha-antiplasmin must be converted to a derivative form for optimal function.
abstract: BACKGROUND
  Human alpha(2)-antiplasmin (alpha(2)AP), the primary inhibitor of fibrinolysis, is secreted from the liver into plasma as a 464-residue protein with Met as the N-terminus. An R6W polymorphism has been suggested to affect fibrinolytic rate. Within circulating blood, antiplasmin-cleaving enzyme (APCE) cleaves Met-alpha(2)AP(R6) faster than Met-alpha(2)AP(W6) at the Pro12-Asn13 bond to yield Asn-alpha(2)AP.
  
  
  OBJECTIVE
  To compare Met-alpha(2)AP(R6), Met-alpha(2)AP(W6) and Asn-alpha(2)AP for crosslinking with fibrin and the ability to protect fibrin from digestion by plasmin.
  
  
  RESULTS
  Asn-alpha(2)AP utilizes Gln2 (Gln14 in Met-alpha(2)AP) to become crosslinked to fibrin approximately twelvefold faster than Met-alpha(2)AP(R6) or Met-alpha(2)AP(W6), and this enhances the resistance of fibrin to plasmin. All three forms of alpha(2)AP inhibit plasmin at identical rates. The N-terminal 12-residue peptide of Met-alpha(2)AP slows crosslinking of Met-alpha(2)AP(R6) or Met-alpha(2)AP(W6) by limiting access of factor XIIIa to Gln14 rather than shifting crosslinking to other Gln residues. Edman sequencing and mass analyses of tryptic peptides from each alpha(2)AP crosslinked with 5-(biotinamido)pentylamine showed Gln14 as the only major crosslinking site. Residues 5-8, GRQL in Met-alpha(2)AP(R6), and residues 1-8, MEPLGWQL in Met-alpha(2)AP(W6), slow fibrin crosslinking.
  
  
  CONCLUSIONS
  Gln14 in both Met-alpha(2)AP(R6) and Met-alpha(2)AP(W6) is sheltered by the N-terminal 12-residue peptide, which, when cleaved, yields Asn-alpha(2)AP, which is rapidly crosslinked to fibrin and maximally protects it from plasmin. The R6 W polymorphism in Met-alpha(2)AP does not affect its crosslinking to fibrin, but it does slow cleavage by APCE and reduces the amount of Asn-alpha(2)AP available for rapid crosslinking to fibrin.
authors: William K. Warren Medical Research Center and Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73190, USA. kyung-lee@ouhsc.edu
authors: K N
authors: KN
authors: Lee
authors: K W
authors: KW
authors: Jackson
authors: V J
authors: VJ
authors: Christiansen
authors: C S
authors: CS
authors: Lee
authors: J G
authors: JG
authors: Chun
authors: P A
authors: PA
authors: McKee
mesh_terms: D000588:Amines / Q000737:chemistry; D000951:Antigens, Neoplasm / Q000737:chemistry; D014408:Biomarkers, Tumor / Q000737:chemistry; D001710:Biotin / Q000031:analogs & derivatives / Q000737:chemistry; D002846:Chromatography, Affinity; D003432:Cross-Linking Reagents / Q000737:chemistry; D010450:Endopeptidases; D005176:Factor XIII / Q000378:metabolism; D005337:Fibrin / Q000737:chemistry; D005342:Fibrinolysis; D018093:Gelatinases; D006801:Humans; D008099:Liver / Q000378:metabolism; D008565:Membrane Proteins; D008954:Models, Biological; D010455:Peptides / Q000737:chemistry; D011110:Polymorphism, Genetic; D017434:Protein Structure, Tertiary; D012697:Serine Endopeptidases / Q000737:chemistry; D000979:alpha-2-Antiplasmin / Q000378:metabolism*; D000099167:Fibroblast Activation Protein Alpha
chemical_list: D000588:Amines; D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D001710:Biotin; D003432:Cross-Linking Reagents; D010450:Endopeptidases; D005176:Factor XIII; D005337:Fibrin; D018093:Gelatinases; D008565:Membrane Proteins; D010455:Peptides; D012697:Serine Endopeptidases; D000979:alpha-2-Antiplasmin; D000099167:Fibroblast Activation Protein Alpha; C076022:5-(biotinamido)pentylamine; C487177:antiplasmin-cleaving enzyme, human