N1421K mutation in the glycoprotein Ib binding domain impairs ristocetin‐ and botrocetin‐mediated binding of von Willebrand factor to platelets

Abstract

von Willebrand disease (VWD) is a common inheritable bleeding disorder caused by deficiency of von Willebrand Factor (VWF), which is involved in platelet adhesion and aggregation. We report a family consisting of three patients with VWD characterized by an apparently normal multimeric pattern, moderately decreased plasma factor VIII (FVIII) and VWF levels, and disproportionately low-plasma VWF:RCo levels. The patients were found to be heterozygous for the novel N1421K mutation, caused by a 4263C > G transversion in exon 28 of the VWF gene coding for the A1 domain. Botrocetin- and ristocetin-mediated binding of plasma VWF to GPIb were reduced in the patients. In vitro mutagenesis and expression in COS-7 cells confirmed the impairment of the mutant in botrocetin- and ristocetin-mediated VWF binding to GPIb. VWF collagen binding capacity was unaffected in plasma from the heterozygous individuals as well as in medium from transfected COS-7 cells. Our findings indicate that the N1421K substitution in the VWF affects the GPIb binding site or a recognition element by a conformational change of the A1 domain.

Mutant botrocetin‐2 inhibits von Willebrand factor‐induced platelet agglutination

“…It will also be interesting to clarify whether rBot2 can bind to the mutant VWFs found in VWD individuals, such as in those with type 2M VWD, which show a normal multimer pattern but reduced GPIb binding in the presence of ristocetin or botrocetin . Several mutations have been found in the VWFs from type 2M VWD individuals, such as missense (Ser1285Phe, Phe1369Ile, Asn1421Lys, and Ile1425Phe) or deletion (Arg1392–Gln1492) mutations . These mutations in the A1 domain affect the binding sites for ristocetin, botrocetin, and/or GPIb.…”