title: Critical von Willebrand factor A1 domain residues influence type VI collagen binding.
abstract: BACKGROUND
  von Willebrand factor (VWF) binds to subendothelial collagen at sites of vascular injury. Laboratory testing for von Willebrand disease (VWD), however, does not always include collagen binding assays (VWF:CB) and standard VWF:CB assays use type I and/or type III collagen rather than type VI collagen.
  
  
  OBJECTIVE
  We report here on several mutations that exclusively alter binding to type VI collagen.
  
  
  METHODS
  Healthy controls and index cases from the Zimmerman Program for the Molecular and Clinical Biology of VWD were analyzed for VWF antigen (VWF:Ag), VWF ristocetin cofactor activity and VWF:CB with types I, III and VI collagen. VWF gene sequencing was performed for all subjects.
  
  
  RESULTS
  Two healthy controls and one type 1 VWD subject were heterozygous for an A1 domain sequence variation, R1399H, and displayed a selective decreased binding to type VI collagen but not types I and III. Expression of recombinant 1399H VWF resulted in absent binding to type VI collagen. Two other VWF A1 domain mutations, S1387I and Q1402P, displayed diminished binding to type VI collagen. An 11 amino acid deletion in the A1 domain also abrogated binding to type VI collagen.
  
  
  CONCLUSIONS
  VWF:CB may be useful in diagnosis of VWD, as a decreased VWF:CB/VWF:Ag ratio may reflect specific loss of collagen binding ability. Mutations that exclusively affect type VI collagen binding may be associated with bleeding, yet missed by current VWF testing.
authors.affiliation: Department of Pediatrics, Division of Hematology/Oncology, Medical College of Wisconsin, Milwaukee, WI 53201-2178, USA. vflood@mcw.edu
authors.forename: V H
authors.initials: VH
authors.lastname: Flood
authors.forename: J C
authors.initials: JC
authors.lastname: Gill
authors.forename: P A
authors.initials: PA
authors.lastname: Christopherson
authors.forename: D B
authors.initials: DB
authors.lastname: Bellissimo
authors.forename: K D
authors.initials: KD
authors.lastname: Friedman
authors.forename: S L
authors.initials: SL
authors.lastname: Haberichter
authors.forename: S R
authors.initials: SR
authors.lastname: Lentz
authors.forename: R R
authors.initials: RR
authors.lastname: Montgomery
mesh_terms: D016022:Case-Control Studies; D024142:Collagen Type VI / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008958:Models, Molecular; D009154:Mutation; D010375:Pedigree; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014841:von Willebrand Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D024142:Collagen Type VI; D011994:Recombinant Proteins; D014841:von Willebrand Factor