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A discontinuous autoinhibitory module masks the A1 domain of von Willebrand factor.

ABSTRACT: Essentials The mechanism for the auto-inhibition of von Willebrand factor (VWF) remains unclear. Hydrogen exchange of two VWF A1 fragments with disparate activities was measured and compared. Discontinuous residues flanking A1 form a structural module that blocks A1 binding to the platelet. Our results suggest a potentially unified model of VWF activation. Click to hear an ISTH Academy presentation on the domain architecture of VWF and activation by elongational flow by Dr Springer SUMMARY: Background How von Willebrand factor (VWF) senses and responds to shear flow remains unclear. In the absence of shear flow, VWF or its fragments can be induced to bind spontaneously to platelet GPIb?. Objectives To elucidate the auto-inhibition mechanism of VWF. Methods Hydrogen-deuterium exchange (HDX) of two recombinant VWF fragments expressed from baby hamster kidney cells were measured and compared. Results The shortA1 protein contains VWF residues 1261-1472 and binds GPIb? with a significantly higher affinity than the longA1 protein that contains VWF residues 1238-1472. Both proteins contain the VWF A1 domain (residues 1272-1458). Many residues in longA1, particularly those in the N- and C-terminal sequences flanking the A1 domain, and in helix ?1, loops ?1?2 and ?3?2, demonstrated markedly reduced HDX compared with their counterparts in shortA1. The HDX-protected region in longA1 overlaps with the GPIb?-binding interface and is clustered with type 2B von Willebrand disease (VWD) mutations. Additional comparison with the HDX of denatured longA1 and ristocetin-bound longA1 indicates the N- and C-terminal sequences flanking the A1 domain form cooperatively an integrated autoinhibitory module (AIM) that interacts with the HDX-protected region. Binding of ristocetin to the C-terminal part of the AIM desorbs the AIM from A1 and enables longA1 binding to GPIb?. Conclusion The discontinuous AIM binds the A1 domain and prevents it from binding to GPIb?, which has significant implications for the pathogenesis of type 2B VWD and the shear-induced activation of VWF activity.

SUBMITTER: Deng W

PROVIDER: S-EPMC5585049 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature

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A discontinuous autoinhibitory module masks the A1 domain of von Willebrand factor.

Deng W W Wang Y Y Druzak S A SA Healey J F JF Syed A K AK Lollar P P Li R R

Journal of thrombosis and haemostasis : JTH 20170809 9

Essentials The mechanism for the auto-inhibition of von Willebrand factor (VWF) remains unclear. Hydrogen exchange of two VWF A1 fragments with disparate activities was measured and compared. Discontinuous residues flanking A1 form a structural module that blocks A1 binding to the platelet. Our results suggest a potentially unified model of VWF activation. Click to hear an ISTH Academy presentation on the domain architecture of VWF and activation by elongational flow by Dr Springer SUMMARY: Back ...[more]

PMID: 28692141

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Project description:Essentials The self-inhibitory mechanism of von Willebrand factor (VWF) remains unclear. Residues flanking the A1 domain of VWF form a discontinuous autoinhibitory module (AIM). rVWF1238-1493 exhibited greater thermostability and inactivity than its shorter counterparts. The cooperative coupling between the N- and C- AIM regions are required for inhibiting A1.SummaryBackground The hierarchical hemostasis response involves a self-inhibitory feature of von Willebrand factor (VWF) that has not been fully characterized. The residues flanking the A1 domain of VWF are important in this self-inhibition by forming an autoinhibitory module (AIM) that masks the A1 domain. Objectives To delimit the AIM sequence and to evaluate the cooperative interplay between the discontinuous AIM regions. Methods ELISA, flow cytometry, a thermal stability assay and hydrogen-deuterium exchange (HDX) mass spectrometry were used to characterize recombinant VWF A1 fragments varying in length. Results The longest A1 fragment (rVWF1238-1493 ) showed higher inactivity in binding the platelet receptor glycoprotein (GP) Ibα and greater thermostability than its shorter counterparts. The HDX results showed that most of the N-terminal residues and residues 1459-1478 at the C-terminus of rVWF1238-1493 have slower deuterium uptake than the residues in its denatured counterpart, implying that these residues may interact with the A1 domain. In contrast, residues 1479-1493 showed less difference from the denatured form, indicating that these residues are unlikely to be involved in binding the A1 domain. The A1 fragment that lacks either the entire C-terminal flanking region of the AIM (C-AIM), i.e. rVWF1238-1461 , or the entire N-terminal flanking region of the AIM (N-AIM), i.e. rVWF1271-1493 , showed high GPIbα-binding affinity and low thermostability, suggesting that removal of either N-terminal or C-terminal residues resulted in loss of AIM inhibition of the A1 domain. Conclusion The AIM is probably composed of residues 1238-1271 (N-AIM) and 1459-1478 (C-AIM). Neither the N-AIM nor the C-AIM alone could fully inhibit binding of the A1 domain to GPIbα.

Dataset Information

A discontinuous autoinhibitory module masks the A1 domain of von Willebrand factor.

Publications

A discontinuous autoinhibitory module masks the A1 domain of von Willebrand factor.

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