title: A new mutation, S1285F, within the A1 loop of von Willebrand factor induces a conformational change in A1 loop with abnormal binding to platelet GPIb and botrocetin causing type 2M von Willebrand disease.
abstract: We report the identification of a new mutation in exon 28 of the von Willebrand factor (VWF) gene in two related patients with type 2M von Willebrand disease (VWD). The molecular abnormality changes the Ser 1285 to Phe within the A1 loop of VWF. The S1285F mutation was reproduced by site-directed mutagenesis on the full-length VWF cDNA. The mutated recombinant VWF (rVWF), F1285rVWF, and the hybrid, S/F1285rVWF, were expressed in COS-7 cells. F1285rVWF exhibited a slight decrease of high-molecular-weight multimers and markedly reduced ristocetin- or botrocetin-induced binding of VWF to platelets in association with a decreased binding to botrocetin. The hybrid S/F1285rVWF showed a normal multimeric profile and bound to platelets in a similar way to the patients' plasma VWF, in the presence of ristocetin or botrocetin. Thus, the new S1285F mutation within the A1 loop was responsible for the type 2M VWD observed in these patients, and was involved in the binding of VWF to botrocetin and to platelet glycoprotein Ib (GPIb). Three anti-VWF monoclonal antibodies, with conformational epitopes within the A1 loop but distinct GPIb binding inhibitory properties, showed a different interaction with F1285rVWF. These results indicate that the S1285F substitution alters the folding of the A1 loop and prevents the correct exposure of the VWF binding sites to botrocetin and GPIb.
authors.affiliation: INSERM U143, Bicêtre, Lille, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Stepanian
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Ribba
authors.forename: Jean-Maurice
authors.initials: JM
authors.lastname: Lavergne
authors.forename: Edith
authors.initials: E
authors.lastname: Fressinaud
authors.forename: Irene
authors.initials: I
authors.lastname: Juhan-Vague
authors.forename: Claudine
authors.initials: C
authors.lastname: Mazurier
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Girma
authors.forename: Dominique
authors.initials: D
authors.lastname: Meyer
mesh_terms: D000328:Adult; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D001792:Blood Platelets / Q000378:metabolism; D019556:COS Cells; D003435:Crotalid Venoms / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008297:Male; D009154:Mutation; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D012310:Ristocetin / Q000378:metabolism; D014842:von Willebrand Diseases / Q000235:genetics*; D014841:von Willebrand Factor / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D003435:Crotalid Venoms; D019038:Platelet Glycoprotein GPIb-IX Complex; D011994:Recombinant Proteins; D014841:von Willebrand Factor; D012310:Ristocetin; C030961:botrocetin