Basic Science ReviewA Tale of Three Proteins

by

Jack B. Alperin, MD, FACP

The Proteins Are…

• Von Willebrand Factor• Factor VIII• ADAMTS 13

von Willebrand Factor

Gene Location Chr. 12p 12.2 - 12.3Synthetic Site EndotheliumMol. Weight 0.5 - 20 MDFunction Essential for both 1st

and 2nd hemostasis

Factor VIII

Gene Location Chr. Xq28Cellular Origin Hepatic sinusoidal

endothelial cellsMol. Weight L 80 KD, H 90 - 200 KDFunction Coag. cascade leading to

a stable fibrin thrombus

ADAMTS 13*

Gene Location Chr. 9q 34Cellular Origin Hepatic stellate cellsMol. Weight 150 KDFunction VWF proteinase splits the amino bond at …

-842(Tyr) - 843(Meth)-

*a disintegrin and metalloproteinase with thrombospondin 1 motif 13

von Willebrand FactorRole in Primary Hemostasis• Platelet adhesion to collagen at

sites of vascular injury• Platelet aggregation at sites of

vascular injury

Role in Secondary Hemostasis• Binds and stabilizes factor VIII

in plasma• Transports factor VIII to sites of

vascular injury

von Willebrand Factor Monomer

NH2-SER-ARG-VAL-LYS-GLY-GLU-ARG-GLY-ASP-SER-LYS-COOH

1 272 449 728 911 1365 1744 1747 2050

Factor VIII GPIbCollagen

Collagen GPIIb/IIIa

Polymerization of VWFER

N C

S

S

N C{Dimer

Golgi

N C

N C

N C

N C

S

S

S

S

S

S} Multimer

Definitions

VWF:RCoA property of VWF that supports ristocetin- induced aggregation of normal platelets. Commonly called ristocetin cofactor activity.

VWF Multimer Analysis Multimers of different molecular weights found in plasma by chromatography and electrophoresis.

VWF:AgAn antigenic determinant on the VWF measured by an immunoassay using a heterologous or monoclonal antibody.

1.Normal

2.VWD Type 1

3.VWD Type 2a

4.Normal

X-ChromosomeSinusoidalLiver Cells

(2332 aa) F.VIII precursor

*(variable) F.VIII molecule

Chromosome 12Endothelial CellsMegakaryocytes

Pre-Pro-VWF (2813 aa)

VWF monomer (2050 aa)

VWF multimer (0.5-20 x106K)

(F.VIII) – (VWF) Complex

*light chain 80 x 103D heavy chain 90-200 x 103D

1ULVWF 2VWFCP VWFmultimers multimers

ENDOTHELIAL CELL

1. Ultra Large von Willebrand Factor Multimers

2. von Willebrand Factor Cleaving Proteinase or ADAMTS 13

von Willebrand Factor Cleaving Proteinase(ADAMTS13)

• Absent in inherited TTP• Inhibited by antibodies in acquired TTP• Recombinant form may be used to treat TTP• Destroys specific VWF mutations causing some forms

of VWD Type 1 and Type 2a• Variant may be a risk factor for myocardial infarction

The von Willebrand Factor Cleaving Proteinase(ADAMTS13)*

Gene location - Chr. 9q34, 29 exons

Synthesis - Stellate Cells in Liver Structure – 1427 aa, Mr 150 KD Half-life 2-4 Days Splits the amino bond between -842 (Tyr) - 843 (Meth)-

Most effective when substrate (VWF) is denatured by shear stress

*ADAMTS 13 - (a disintegrin and metalloproteinase with thrombospodin 1 motif 13)