The complete N-terminal extension of heparin cofactor II is required for maximal effectiveness as a thrombin exosite 1 ligand

BACKGROUND: Heparin cofactor II (HCII) is a circulating protease inhibitor, one which contains an N-terminal acidic extension (HCII 1-75) unique within the serpin superfamily. Deletion of HCII 1-75 greatly reduces the ability of glycosaminoglycans (GAGs) to accelerate the inhibition of thrombin, and abrogates HCII binding to thrombin exosite 1. While a minor portion of HCII 1-75 can be visualized in a crystallized HCII-thrombin S195A complex, the role of the rest of the extension is not well understood and the affinity of the HCII 1-75 interaction has not been quantitatively characterized. To address these issues, we expressed HCII 1-75 as a small, N-terminally hexahistidine-tagged polypeptide in E. coli. RESULTS: Immobilized purified HCII 1-75 bound active α-thrombin and active-site inhibited FPR-ck- or S195A-thrombin, but not exosite-1-disrupted γT-thrombin, in microtiter plate assays. Biotinylated HCII 1-75 immobilized on streptavidin chips bound α-thrombin and FPR-ck-thrombin with similar KD values of 330-340 nM. HCII 1-75 competed thrombin binding to chip-immobilized HCII 1-75 more effectively than HCII 54-75 but less effectively than the C-terminal dodecapeptide of hirudin (mean Ki values of 2.6, 8.5, and 0.29 μM, respectively). This superiority over HCII 54-75 was also demonstrated in plasma clotting assays and in competing the heparin-catalysed inhibition of thrombin by plasma-derived HCII; HCII 1-53 had no effect in either assay. Molecular modelling of HCII 1-75 correctly predicted those portions of the acidic extension that had been previously visualized in crystal structures, and suggested that an α-helix found between residues 26 and 36 stabilizes one found between residues 61-67. The latter region has been previously shown by deletion mutagenesis and crystallography to play a crucial role in the binding of HCII to thrombin exosite 1. CONCLUSIONS: Assuming that the KD value for HCII 1-75 of 330-340 nM faithfully predicts that of this region in intact HCII, and that 1-75 binding to exosite 1 is GAG-dependent, our results support a model in which thrombin first binds to GAGs, followed by HCII addition to the ternary complex and release of HCII 1-75 for exosite 1 binding and serpin mechanism inhibition. They further suggest that, in isolated or transferred form, the entire HCII 1-75 region is required to ensure maximal binding of thrombin exosite 1.

Abstract aus PubMed (NCBI) für den zitierten Eintrag, in der Originalsprache wiedergegeben. Maßgeblich ist die Fassung der Originalpublikation.

Das Abstract wird nicht übersetzt, damit die eigene Wortwahl der Autoren erhalten bleibt.

Recombinant HCII 1-75 bound thrombin exosite 1 with KD 330-340 nM and competed for binding less potently than hirudin's C-terminal dodecapeptide (Ki 2.6 versus 0.29 μM), indicating the entire extension is required for maximal exosite 1 engagement.

Erfahren Sie, wie diese Forschung mit der klinischen Praxis verknüpft ist

Weitere begutachtete Studien in der Kategorie „Genomik & Proteomik“.

• Leech Salivary Proteome and Transcriptome: 434 Deduced Protein Sequences — Liu Z, Tong X, Su Y, et al. (2019)
• Medicinal Leech Draft Genome — Anticoagulant Gene Survey — Kvist S, Manzano-Marín A, de Carle D, Trontelj P, Siddall ME (2020)
• Blutegeltherapie (Hirudo medicinalis) mildert die durch testikuläre Ischämie/Reperfusion induzierten Hodenschäden in einem Tiermodell — Davoodi F et al. (2021)
• Neues antikoagulatorisches Protein aus dem medizinischen Blutegel — Manuvera V et al. (2024)
• AIF-1 und RNASET2 spielen komplementäre Rollen in der angeborenen Immunantwort des medizinischen Blutegels — Baranzini N et al. (2019)
• Antimikrobielle Peptide des medizinischen Blutegels ohne Toxizität stellen eine vielversprechende alternative Strategie zur Bekämpfung antibiotikaresistenter Erreger dar — Grafskaia E et al. (2019)
• Structural insights into thrombolytic activity of destabilase from medicinal leech — Marin E et al. (2023)
• Das Genom des medizinischen Blutegels (Whitmania pigra) und eine vergleichende Genomstudie zur Erforschung bioaktiver Inhaltsstoffe — Tong L et al. (2022)
• Das ZNS des medizinischen Blutegels als Modell für Exosomen-Studien zum Wechselspiel zwischen Mikroglia und Neuronen — Raffo-Romero A et al. (2018)
• Transcriptomic profiling and the first spatial expression analysis of candidate genes in the salivary gland of the East Asian medicinal leech, Hirudo nipponia — Kim J et al. (2024)

Alle von der ASH analysierten Studien →