title: pH-Dependent Interactions in Dimers Govern the Mechanics and Structure of von Willebrand Factor.
abstract: Von Willebrand factor (VWF) is a multimeric plasma glycoprotein that is activated for hemostasis by increased hydrodynamic forces at sites of vascular injury. Here, we present data from atomic force microscopy-based single-molecule force measurements, atomic force microscopy imaging, and small-angle x-ray scattering to show that the structure and mechanics of VWF are governed by multiple pH-dependent interactions with opposite trends within dimeric subunits. In particular, the recently discovered strong intermonomer interaction, which induces a firmly closed conformation of dimers and crucially involves the D4 domain, was observed with highest frequency at pH 7.4, but was essentially absent at pH values below 6.8. However, below pH 6.8, the ratio of compact dimers increased with decreasing pH, in line with a previous transmission electron microscopy study. These findings indicated that the compactness of dimers at pH values below 6.8 is promoted by other interactions that possess low mechanical resistance compared with the strong intermonomer interaction. By investigating deletion constructs, we found that compactness under acidic conditions is primarily mediated by the D4 domain, i.e., remarkably by the same domain that also mediates the strong intermonomer interaction. As our data suggest that VWF has the highest mechanical resistance at physiological pH, local deviations from physiological pH (e.g., at sites of vascular injury) may represent a means to enhance VWF's hemostatic activity where needed.
authors.affiliation: Department of Physics and Center for Nanoscience, LMU Munich, Munich, Germany. Electronic address: jochen.mueller@physik.uni-muenchen.de.
authors.forename: Jochen P
authors.initials: JP
authors.lastname: Müller
authors.affiliation: Department of Physics and Center for Nanoscience, LMU Munich, Munich, Germany.
authors.forename: Achim
authors.initials: A
authors.lastname: Löf
authors.affiliation: Department of Physics and Center for Nanoscience, LMU Munich, Munich, Germany.
authors.forename: Salomé
authors.initials: S
authors.lastname: Mielke
authors.affiliation: Department of Pediatric Hematology and Oncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Obser
authors.affiliation: Department of Physics and Center for Nanoscience, LMU Munich, Munich, Germany.
authors.forename: Linda K
authors.initials: LK
authors.lastname: Bruetzel
authors.affiliation: Department of Physics and Center for Nanoscience, LMU Munich, Munich, Germany; Department of Chemistry, Division of Molecular Imaging and Photonics, KU Leuven-University of Leuven, Leuven, Belgium.
authors.forename: Willem
authors.initials: W
authors.lastname: Vanderlinden
authors.affiliation: Department of Physics and Center for Nanoscience, LMU Munich, Munich, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Lipfert
authors.affiliation: Department of Pediatric Hematology and Oncology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Schneppenheim
authors.affiliation: Department of Physics and Center for Nanoscience, LMU Munich, Munich, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Benoit
mesh_terms: D000595:Amino Acid Sequence; D001696:Biomechanical Phenomena; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D055595:Mechanical Phenomena; D055503:Protein Multimerization / Q000187:drug effects; D020836:Protein Structure, Quaternary; D014841:von Willebrand Factor / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D007093:Imidazoles; D014841:von Willebrand Factor; C029899:imidazole