Structure-resolved dynamics of type 2M von Willebrand disease

Area of Science:

• Biochemistry
• Molecular Biology
• Hematology

Background:

• Genetically determined amino acid substitutions in the platelet adhesive A1 domain of von Willebrand factor (VWF) cause gain- (type 2B) or loss-of-function (type 2M) phenotypes of von Willebrand disease.
• Prior studies indicated that structural defects, including misfolding and hyperstabilization, alter the stability and folding of the A1 domain.

Purpose of the Study:

• To investigate the structure/function relationships of 15 additional type 2M variants and 2 polymorphisms in the VWF A1 domain.
• To fully understand the molecular mechanisms underlying the type 2M von Willebrand disease phenotype.

Main Methods:

• Circular dichroism, fluorescence, and calorimetry were used to assess protein structure and stability.
• Hydrogen-deuterium exchange mass spectrometry and surface plasmon resonance were employed to analyze protein dynamics and binding affinities.
• Platelet adhesion under shear flow was measured to evaluate functional consequences.

Main Results:

• Six variants were natively folded, with four exhibiting hyperstabilization.
• Nine variants showed disordered A1 domains, characterized by reduced α-helical structure and unfolding enthalpy.
• GPIbα binding affinity and platelet adhesion dynamics strongly correlated with helical structure, with localized structural perturbations significantly diminishing binding affinity and shear-dependent adhesion.

Conclusions:

• Hyperstabilized dynamics in the A1 domain can impair platelet attachment to VWF under flow.
• Variant-induced localized disorder in specific A1 domain regions leads to misfolding and abrogated platelet adhesion.
• These opposing conformational properties represent two distinct structural classes of VWF that drive the type 2M von Willebrand disease phenotype.