title: Calcium modulates force sensing by the von Willebrand factor A2 domain.
abstract: von Willebrand factor (VWF) multimers mediate primary adhesion and aggregation of platelets. VWF potency critically depends on multimer size, which is regulated by a feedback mechanism involving shear-induced unfolding of the VWF-A2 domain and cleavage by the metalloprotease ADAMTS-13. Here we report crystallographic and single-molecule optical tweezers data on VWF-A2 providing mechanistic insight into calcium-mediated stabilization of the native conformation that protects A2 from cleavage by ADAMTS-13. Unfolding of A2 requires higher forces when calcium is present and primarily proceeds through a mechanically stable intermediate with non-native calcium coordination. Calcium further accelerates refolding markedly, in particular, under applied load. We propose that calcium improves force sensing by allowing reversible force switching under physiologically relevant hydrodynamic conditions. Our data show for the first time the relevance of metal coordination for mechanical properties of a protein involved in mechanosensing.
authors.affiliation: Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Department of Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Arjen J
authors.initials: AJ
authors.lastname: Jakobi
authors.forename: Alireza
authors.initials: A
authors.lastname: Mashaghi
authors.forename: Sander J
authors.initials: SJ
authors.lastname: Tans
authors.forename: Eric G
authors.initials: EG
authors.lastname: Huizinga
mesh_terms: D051722:ADAM Proteins / Q000378:metabolism; D000071120:ADAMTS13 Protein; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D003461:Crystallography; D006801:Humans; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D052898:Optical Tweezers; D011487:Protein Conformation; D011489:Protein Denaturation; D055550:Protein Stability; D014841:von Willebrand Factor / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D014841:von Willebrand Factor; D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human; D002118:Calcium