Subunit composition of oligomeric human von Willebrand factor

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Von Willebrand factor (vWf) is essential for primary hemostasis.
• The oligomerization of vWf is critical for its function but not fully understood.
• Endothelial cells synthesize and secrete vWf.

Purpose of the Study:

• To investigate the oligomerization process of human endothelial cell-synthesized vWf.
• To identify the molecular composition of high molecular weight (Mr) vWf oligomers.
• To elucidate the role of precursor subunits in vWf assembly.

Main Methods:

• Gel chromatography using Sephacryl S-500.
• Discontinuous agarose gel electrophoresis.
• Immunoprecipitation with a monoclonal anti-vWf-Sepharose adduct.
• Analysis of [35S]methionine-labeled cell lysates and culture media.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions.

Main Results:

• High Mr vWf oligomers were successfully recovered from endothelial cell lysates and culture media.
• These high Mr oligomers are composed of Mr 225,000 subunits.
• The precursor vWf subunit (provWf, Mr 240,000) was primarily observed as dimers, indicating limited further oligomerization.
• Oligomerization appears to involve mature vWf subunits rather than precursor subunits.

Conclusions:

• Von Willebrand factor (vWf) oligomerization is primarily mediated by mature vWf subunits.
• The conversion of provWf to mature vWf subunits, likely through proteolytic processing, facilitates vWf oligomerization.
• This processing step is essential for the formation of functional high Mr vWf oligomers.