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Von Willebrand Factor A2 Domain

VWF A2 Domain PDB ID:3GXB (Zhang et al.)

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This is the crystal structure of the VWF A2 domain, PDB ID 3GXB, elucidated by Zhang, et al.[1] Von Willebrand factor (VWF) is a large multimeric glycoprotein with a critical role in maintaining hemostasis. VWF serves as the carrier protein for the plasma coagulation protein factor VIII (FVIII) and promotes platelet adhesion and aggregation at the sites of vascular damage.[2] The hemostatic potential of VWF greatly increases with the multimer size, which is tightly regulated in vivo by the metalloprotease ADAMTS13.[3][4][5]

ADAMTS13 is the thirteenth member of the A disintegrin-like and metalloprotease with thrombospondin type 1 motif family of proteases. ADAMTS13 cleaves VWF between and maintains plasma VWF within a normal molecular weight range by cleaving high molecular weight (HMW) multimers soon after they are secreted into the plasma, preventing spontaneous platelet agglutination. [3][4][5]

The is not stabilized by disulfide bonds within VWF, unlike A1 and A3. In addition, the A2 domain lacks the highly conserved α4 helix, which has been replaced with the flexible and dynamic .[1] This leads to low resistance to unfolding, giving the A2 domain the function of a shear bolt. A shear bolt breaks above a designed force threshold, to protect other parts of a machine from accidental damage. Similarly, the A2 domain unfolds when present in VWF multimers that experience high tensile force and is cleaved by ADAMTS13, resulting in down regulation of the hemostatic activity.[6] VWF will only be exposed to peak shear forces intermittently in the arterioles in normal circulation, but when tethered, VWF will undergo longer, higher shear rates, causing the A2 domain to unfold and allowing ADAMTS13 access to the A2 domain’s central cleavage site.[1] These shear forces will increase at sites of vascular damage with a growing thrombus that narrows vessel diameter. ADAMTS13 serves to halt the growth of the thrombus to prevent vessel occlusion, as has been demonstrated in vitro.[7] The minimal substrate for ADAMTS13 cleavage is the A2 domain’s D1596-R1668, .[8] Several exosites in ADAMTS13 interact with the VWF A2 domain to contribute to substrate specificity and enhance cleavage efficiency. The TSP1 spacer domain in ADAMTS13 interacts with VWF residues between Gln1624 and Arg1668.[9] The exosite binding was further refined to identify three additional exosites, the first involving VWF1596-1623, the second VWF1642-1652, and the third VWF1653-1668, that are exposed when the VWF A2 domain is unfolded.[10]

Type 2A group II von Willebrand disease mutations have increased susceptability to ADAMTS13-mediated proteolysis. These are located in the A2 domain. These include R1597W[11].

is a type 1 von Willebrand disease mutation that has also demonstrated increased ADAMTS13-mediated proteolysis.[11][12] Atoms within 5 angstroms are highlighted. The red circles represent the oxygens in free water molecules around Y1584.

The A2 domain has several naturally occuring single nucleotide polymorphisms that alter the amino acid sequence, and also alter ADAMTS13 mediated cleavage. These include Q/H1571, P/T1601, and .[11][12]

References:

  1. ↑ 1.0 1.1 1.2 Zhang Q, Zhou YF, Zhang CZ, Zhang X, Lu C, Springer TA. Structural specializations of A2, a force-sensing domain in the ultralarge vascular protein von Willebrand factor. Proc Natl Acad Sci U S A. 2009 Jun 9;106(23):9226-31. Epub 2009 May 21. PMID:19470641
  2. ↑ Sadler JE. Biochemistry and genetics of von Willebrand factor. Annu Rev Biochem. 1998;67:395-424. PMID:9759493 doi:10.1146/annurev.biochem.67.1.395
  3. ↑ 3.0 3.1 Furlan M. Von Willebrand factor: molecular size and functional activity. Ann Hematol. 1996 Jun;72(6):341-8. PMID:8767102
  4. ↑ 4.0 4.1 Plaimauer B, Zimmermann K, Volkel D, Antoine G, Kerschbaumer R, Jenab P, Furlan M, Gerritsen H, Lammle B, Schwarz HP, Scheiflinger F. Cloning, expression, and functional characterization of the von Willebrand factor-cleaving protease (ADAMTS13). Blood. 2002 Nov 15;100(10):3626-32. Epub 2002 Jul 12. PMID:12393399 doi:10.1182/blood-2002-05-1397
  5. ↑ 5.0 5.1 Zheng X, Chung D, Takayama TK, Majerus EM, Sadler JE, Fujikawa K. Structure of von Willebrand factor-cleaving protease (ADAMTS13), a metalloprotease involved in thrombotic thrombocytopenic purpura. J Biol Chem. 2001 Nov 2;276(44):41059-63. Epub 2001 Sep 13. PMID:11557746 doi:10.1074/jbc.C100515200
  6. ↑ Zhang X, Halvorsen K, Zhang CZ, Wong WP, Springer TA. Mechanoenzymatic cleavage of the ultralarge vascular protein von Willebrand factor. Science. 2009 Jun 5;324(5932):1330-4. PMID:19498171 doi:324/5932/1330
  7. ↑ Shida Y, Nishio K, Sugimoto M, Mizuno T, Hamada M, Kato S, Matsumoto M, Okuchi K, Fujimura Y, Yoshioka A. Functional imaging of shear-dependent activity of ADAMTS13 in regulating mural thrombus growth under whole blood flow conditions. Blood. 2008 Feb 1;111(3):1295-8. Epub 2007 Oct 10. PMID:17928530 doi:10.1182/blood-2007-09-110700
  8. ↑ Kokame K, Matsumoto M, Fujimura Y, Miyata T. VWF73, a region from D1596 to R1668 of von Willebrand factor, provides a minimal substrate for ADAMTS-13. Blood. 2004 Jan 15;103(2):607-12. Epub 2003 Sep 25. PMID:14512308 doi:10.1182/blood-2003-08-2861
  9. ↑ Gao W, Anderson PJ, Sadler JE. Extensive contacts between ADAMTS13 exosites and von Willebrand factor domain A2 contribute to substrate specificity. Blood. 2008 Sep 1;112(5):1713-9. Epub 2008 May 20. PMID:18492952 doi:10.1182/blood-2008-04-148759
  10. ↑ Akiyama M, Takeda S, Kokame K, Takagi J, Miyata T. Crystal structures of the noncatalytic domains of ADAMTS13 reveal multiple discontinuous exosites for von Willebrand factor. Proc Natl Acad Sci U S A. 2009 Nov 17;106(46):19274-9. Epub 2009 Oct 30. PMID:19880749
  11. ↑ 11.0 11.1 11.2 http://www.vwf.group.shef.ac.uk/ ISTH-SSC VWF Online Database.
  12. ↑ 12.0 12.1 Pruss CM, Notley CR, Hegadorn CA, O'Brien LA, Lillicrap D. ADAMTS13 cleavage efficiency is altered by mutagenic and, to a lesser extent, polymorphic sequence changes in the A1 and A2 domains of von Willebrand factor. Br J Haematol. 2008 Nov;143(4):552-8. PMID:18986390 doi:10.1111/j.1365-2141.2008.07266.x

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