Abstract Number: PB0252
Meeting: ISTH 2020 Congress
Background: The proteases factor XII (FXII) and its homolog hepatocyte growth factor activator (HGFA) contain non-catalytic heavy chains (HC) and catalytic light chains (LC). FXII-HC binds to negatively charged surfaces such as heparin or polyphosphate, enhancing FXII activation by kallikrein and autoactivation. HGFA activation by thrombin is also surface-dependent. In the absence of surface FXII-HC down-regulates FXII activation by kallikrein.
Aims: To compare FXII-HC and HGFA-HC in interactions with charged surfaces and protease activation.
Methods: Recombinant FXII, HGFA, a chimera containing HGFA-HC and FXII-LC (HGFAHCFXIILC), and a chimera containing FXII-HC and HGFA-LC (FXIIHCHGFALC) were prepared. Protein binding to heparin-Sepharose and protein activation were compared.
Results: The human FXII-HC carries a positive charge while FXII-LC is negatively charged. The situation is reversed in HGFA (HGFA-HC negatively charged; HGFA-LC positively charged). The order of protein affinity for heparin was FXIIHCHGFALC > FXII > HGFA. HGFAHCFXIILC did not bind heparin. These results are consistent with the charges on the different chains. Interestingly, while neither chimera autoactivated in the presence of polyphosphate, HGFAHCFXIILC autoactivated on a positively charged surface (polyethyleneimine). In the absence of surface, HGFAHCFXIILC activation by kallikrein and FXIIHCHGFALC by thrombin were substantially faster than FXII and HGFA activation by the respective proteases. Unlike FXII and HGFA activation, HGFAHCFXIILC and FXIIHCHGFALC activation were not enhanced by surface.
Conclusions: While FXII binds surfaces via positive charges on its HC, HGFA probably binds through positive charges on its LC. The capacity of HGFAHCFXIILC to autoactivate on polyethyleneimine emphasizes the importance of charge interactions in surface-dependent FXII activation. Enhanced activation of HGFAHCFXIILC and FXIIHCHGFALC relative to FXII and HGFA in the absence of surface indicates the HCs of both FXII and HGFA normally inhibit surface-independent activation, probably by masking the activation cleavage sites, and that this process is disrupted in the chimeras.
To cite this abstract in AMA style:Shamanaev A, Ivanov I, Sun M-, Gailani D. Importance of the Non-Catalytic Heavy Chains of the Homologs Factor XII and HGFA in Protease Function [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/importance-of-the-non-catalytic-heavy-chains-of-the-homologs-factor-xii-and-hgfa-in-protease-function/. Accessed May 6, 2021.
« Back to ISTH 2020 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/importance-of-the-non-catalytic-heavy-chains-of-the-homologs-factor-xii-and-hgfa-in-protease-function/