Delimiting the autoinhibitory module of von Willebrand factor
Author(s): ,
W. Deng
Affiliations:
Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Emory University School of Medicine, Atlanta, USA
Correspondence: Wei Deng, Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Emory University School of Medicine, 2015 Uppergate Drive NE, Room 410, Atlanta, GA 30322, USA|Tel.: +1 404 712 8537|E‐mail: wei.deng@emory.edu
,
K. M. Voos
Affiliations:
Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Emory University School of Medicine, Atlanta, USA
,
J. K. Colucci
Affiliations:
Department of Biochemistry, Emory University School of Medicine, Atlanta, USA
,
E. R. Legan
Affiliations:
Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Emory University School of Medicine, Atlanta, USA
,
E. A. Ortlund
Affiliations:
Department of Biochemistry, Emory University School of Medicine, Atlanta, USA
,
P. Lollar
Affiliations:
Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Emory University School of Medicine, Atlanta, USA
R. Li
Affiliations:
Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Emory University School of Medicine, Atlanta, USA
ISTH Academy. Deng W. Oct 4, 2018; 234170

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Background
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 (rVWF) 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 rVWF 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. rVWF, or the entire N‐terminal flanking region of the AIM (N‐AIM), i.e. rVWF, 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.
Keyword(s)
blood platelets, hemostasis, platelet GPIb–IX complex, tandem mass spectrometry, von Willebrand factor
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