Examining thrombin hydrolysis of the factor XIII activation peptide segment leads to a proposal for explaining the cardioprotective effects observed with the factor XIII V34L mutation.
In the blood coagulation cascade, thrombin cleaves fibrinopeptides A and B from fibrinogen revealing sites for fibrin polymerization that lead to insoluble clot formation. Factor XIII stabilizes this clot by catalyzing the formation of intermolecular cross-links in the fibrin network. Thrombin activates the Factor XIII a(2) dimer by cleaving the Factor XIII activation peptide segment at the Arg(37)-Gly(38) peptide bond. Using a high performance liquid chromatography assay, the kinetic constants K(m), k(cat), and k(cat)/K(m) were determined for thrombin hydrolysis of fibrinogen Aalpha-(7-20), Factor XIII activation peptide-(28-41), and Factor XIII activation peptide-(28-41) with a Val(34) to Leu substitution. This Val to Leu mutation has been correlated with protection from myocardial infarction. In the absence of fibrin, the Factor XIII activation peptide-(28-41) exhibits a 10-fold lower k(cat)/K(m) value than fibrinogen Aalpha-(7-20). With the Factor XIII V34L mutation, decreases in K(m) and increases in k(cat) produce a 6-fold increase in k(cat)/K(m) relative to the wild-type Factor XIII sequence. A review of the x-ray crystal structures of known substrates and inhibitors of thrombin leads to a hypothesis that the new Leu generates a peptide with more extensive interactions with the surface of thrombin. As a result, the Factor XIII V34L is proposed to be susceptible to wasteful conversion of zymogen to activated enzyme. Premature depletion may provide cardioprotective effects.
Trumbo
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TA
Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
Maurer
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MC
D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D004789:Enzyme Activation / Q000235:genetics; D005176:Factor XIII / Q000235:genetics* / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D007700:Kinetics; D009203:Myocardial Infarction / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D010455:Peptides / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism*
D036341:Intercellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D010455:Peptides; C061895:factor XIII activation peptide; D005340:Fibrinogen; D005176:Factor XIII; D013917:Thrombin