Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.6 (thromboplastin)
 13,278 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Members of the serpin (serine protease inhibitor) family share a similar backbone structure but expose a variable reactive-site loop, which binds to the catalytic groove of the target protease. Specificity originates in part from the sequence of this loop and also from secondary binding sites that contribute to the inhibitor function. To clarify the intrinsic contribution of the reactive-site loop, alpha1-antichymotrypsin has been utilized as a scaffold to construct chimeras carrying the loop of antithrombin III, protease nexin 1, or alpha1-antitrypsin. Reactive-site loops not only vary in sequence but also in length; therefore, the length of the reactive-site loop was also varied in the chimeras. The efficacy of the specificity transfer was evaluated by measuring the stoichiometry of the reaction, the ability to form an SDS-stable complex, and the association rate constant with a number of potential targets (chymotrypsin, neutrophil elastase, trypsin, thrombin, factor Xa, activated protein C, and urokinase). Overall, substitution of a reactive-site loop was not sufficient to transfer the specificity of a given serpin to alpha1-antichymotrypsin. Specificity of the chimera partly matched that of the loop donor and partly that of the acceptor, whereas the behavior as an inhibitor or a substrate depended upon the targeted protease. Results suggest that, aside from the contributions of the loop sequence and the framework-specific secondary binding sites, an intramolecular control may be essential for productive interaction.
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PMID:Intrinsic specificity of the reactive site loop of alpha1-antitrypsin, alpha1-antichymotrypsin, antithrombin III, and protease nexin I. 919 29

The exposed Serpin reactive centre loop controls the specificity of the serpin proteinase interaction. Mutations within this region have been used to generate novel potentially therapeutic inhibitors. In this study we examine the effect of the serpin scaffold and reactive centre loop length upon the generation of such inhibitors. The reactive centre loop regions, P7-P3', of alpha1-antitrypsin and alpha1-antichymotrypsin were replaced by the corresponding residues of the viral serpin, Serp1, to form AT/Serp1 and ACT/Serp1, respectively. AT/Serp1 formed SDS stable complexes with a range of proteinases with association rate constants for plasmin, tissue plasminogen activator, urokinase, thrombin and factor Xa of approximately 10(4) M(-1)s(-1) and a stoichiometry of inhibition of approximately 1 for all of them. ACT/Serp1, however, formed SDS-stable complexes with only plasmin and thrombin with association rate constant 100-fold slower than AT/Serp1 and an increased stoichiometry of inhibition. The reactive centre loop of ACT/Serp1 is four amino acid residues longer than AT/Serp1. These four additional residues (VETR) were inserted into AT/Serp1 to form AT/Serp1(VETR). AT/Serp1(VETR) formed SDS stable complexes with plasmin, thrombin and tissue plasminogen activator similar to AT/Serp1, however, the association rate constants were 10-fold slower than those observed with AT/Serp1, while the stoichiometry of inhibition remained around 1. These results suggest that the additional reactive centre loop residues effect the rate of initial complex formation by placing the reactive centre loop in a non-ideal conformation. This study demonstrates that both reactive centre loop length and serpin scaffold are important in defining the inhibitory characteristics of a serpin.
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PMID:Protein engineering of chimeric Serpins: an investigation into effects of the serpin scaffold and reactive centre loop length. 993 Jun 74