title: Covalent regulation of ULVWF string formation and elongation on endothelial cells under flow conditions.
abstract: OBJECTIVE
  The adhesion ligand von Willebrand factor (VWF) is a multimeric glycoprotein that mediates platelet adhesion to exposed subendothelium. On endothelial cells, freshly released ultra-large (UL) VWF multimers form long string-like structures to which platelets adhere.
  
  
  METHODS
  The formation and elongation of ULVWF strings were studied in the presence of the thiol-blocking N-ethylmaleimide (NEM). The presence of thiols in ULVWF and plasma VWF multimers was determined by maleimide-PEO(2)-Biotin labeling and thiol-chromatography. Finally, covalent re-multimerization of ULVWF was examined in a cell- and enzyme-free system.
  
  
  RESULTS
  We found that purified plasma VWF multimers adhere to and elongate ULVWF strings under flow conditions. The formation and propagation of ULVWF strings were dose-dependently reduced by blocking thiols on VWF with NEM, indicating that ULVWF strings are formed by the covalent association of perfused VWF to ULVWF anchored to endothelial cells. The association is made possible by the presence of free thiols in VWF multimers and by the ability of (UL) VWF to covalently re-multimerize.
  
  
  CONCLUSIONS
  The data provide a mechanism by which the thrombogenic ULVWF strings are formed and elongated on endothelial cells. This mechanism suggests that the thiol-disulfide state of ULVWF regulates the adhesion properties of strings on endothelial cells.
authors.affiliation: Section of Thrombosis Research, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: H
authors.initials: H
authors.lastname: Choi
authors.forename: Z
authors.initials: Z
authors.lastname: Zhou
authors.forename: L
authors.initials: L
authors.lastname: Nolasco
authors.forename: H J
authors.initials: HJ
authors.lastname: Pownall
authors.forename: J
authors.initials: J
authors.lastname: Voorberg
authors.forename: J L
authors.initials: JL
authors.lastname: Moake
authors.forename: J-F
authors.initials: JF
authors.lastname: Dong
mesh_terms: D002448:Cell Adhesion; D019281:Dimerization; D004220:Disulfides; D042783:Endothelial Cells / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology; D006801:Humans; D010084:Oxidation-Reduction; D010477:Perfusion; D013314:Stress, Mechanical; D013438:Sulfhydryl Compounds; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D004220:Disulfides; D013438:Sulfhydryl Compounds; D014841:von Willebrand Factor