Structural basis for reduced staphylocoagulase-mediated bovine prothrombin activation.

Friedrich R, Panizzi P, Kawabata S, Bode W, Bock PE, Fuentes-Prior P
J Biol Chem. 2006 281 (2): 1188-95

PMID: 16230338 · PMCID: PMC2292465 · DOI:10.1074/jbc.M507957200

Staphylocoagulase (SC) is a protein secreted by the human pathogen, Staphylococcus aureus, that activates human prothrombin (ProT) by inducing a conformational change. SC-bound ProT efficiently clots fibrinogen, thus bypassing the physiological blood coagulation pathway. The crystal structure of a fully active SC fragment, SC-(1-325), bound to human prethrombin 2 showed that the SC-(1-325) N terminus inserts into the Ile(16) pocket of prethrombin 2, thereby inducing expression of a functional catalytic site in the cognate zymogen without peptide bond cleavage. As shown here, SC-(1-325) binds to bovine and human ProT with similar affinity but activates the bovine zymogen only very poorly. By contrast to the approximately 2-fold difference in chromogenic substrate kinetic constants between human thrombin and the SC-(1-325).human (pro)thrombin complexes, SC-(1-325).bovine ProT shows a 3,500-fold lower k(cat)/K(m) compared with free bovine thrombin, because of a 47-fold increase in K(m) and a 67-fold decrease in k(cat). The SC-(1-325).bovine ProT complex is approximately 5,800-fold less active compared with its human counterpart. Comparison of human and bovine fibrinogen as substrates of human and bovine thrombin and the SC-(1-325).(pro)thrombin complexes indicates that the species specificity of SC-(1-325) cofactor activity is determined primarily by differences in conformational activation of bound ProT. These results suggest that the catalytic site in the SC-(1-325).bovine ProT complex is incompletely formed. The current crystal structure of SC-(1-325).bovine thrombin reveals that SC would dock similarly to the bovine proenzyme, whereas the bovine (pro)thrombin-characteristic residues Arg(144) and Arg(145) would likely interfere with insertion of the SC N terminus, thus explaining the greatly reduced activation of bovine ProT.

MeSH Terms (21)

Animals Arginine Binding, Competitive Binding Sites Blood Coagulation Catalytic Domain Cattle Coagulase Crystallography, X-Ray Dose-Response Relationship, Drug Enzyme Precursors Humans Kinetics Models, Molecular Protein Binding Protein Conformation Protein Structure, Secondary Protein Structure, Tertiary Prothrombin Staphylococcus aureus Thrombin

Connections (1)

This publication is referenced by other Labnodes entities: