Agata Anna Nowak

The plasma von Willebrand factor O-glycome comprises a surprising variety of structures including ABH antigens and disialosyl motifs.

Summary.  Background: von Willebrand factor (VWF) is a key component for maintenance of normal hemostasis. Its glycan moieties, accounting for about 20% of its molecular weight, have been shown to affect many of its properties. Previous studies reported correlations between VWF secretion, half‐life and the nature or presence of its N‐glycans, and more importantly between VWF plasma level and the type of N‐linked ABH antigens. Despite the presence of 10 predicted O‐glycosylation sites, the O‐glycome remains poorly characterized, impairing the complete elucidation of its influence on VWF functions. So far only a single glycan structure, a disialyl core 1 glycan, has been identified. Objectives: To define an exhaustive profile of the VWF O‐glycan structures to help the understanding of their role in VWF regulation and properties. Methods: Plasma‐derived VWF O‐linked sugars were isolated and analyzed using state‐of‐the‐art mass spectrometry methodologies. Results and conclusions: We provide here a detailed analysis of the human plasma‐derived VWF O‐glycome. Eighteen O‐glycan structures including both core 1 and core 2 structures are now demonstrated to be present on VWF. Amongst the newly determined structures are unusual tetra‐sialylated core 1 O‐glycans and ABH antigen‐containing core 2 O‐glycans. In conjunction with current models explaining VWF activity, knowledge of the complete O‐glycome will facilitate research aimed at providing a better understanding of the influence of glycosylation on VWF functions.

Mapping the N-glycome of human von Willebrand factor.

vWF (von Willebrand factor) is a key component for maintenance of normal haemostasis, acting as the carrier protein of the coagulant Factor VIII and mediating platelet adhesion at sites of vascular injury. There is ample evidence that vWF glycan moieties are crucial determinants of its expression and function. Of particular clinical interest, ABH antigens influence vWF plasma levels according to the blood group of individuals, although the molecular mechanism underlying this phenomenon remains incompletely understood. The present paper reports analyses of the human plasma vWF N-glycan population using advanced MS. Glycomics analyses revealed approximately 100 distinct N-glycan compositions and identified a variety of structural features, including lactosaminic extensions, ABH antigens and sulfated antennae, as well as bisecting and terminal GlcNAc residues. We estimate that some 300 N-glycan structures are carried by human vWF. Glycoproteomics analyses mapped ten of the consensus sites known to carry N-glycans. Glycan populations were found to be distinct, although many structural features were shared across all sites. Notably, the H antigen is not restricted to particular N-glycosylation sites. Also, the Asn(2635) site, previously designated as unoccupied, was found to be highly glycosylated. The delineation of such varied glycan populations in conjunction with current models explaining vWF activity will facilitate research aimed at providing a better understanding of the influence of glycosylation on vWF function.

Characterisation of von Willebrand factor A1 domain mutants I1416N and I1416T: correlation of clinical phenotype with flow‐based platelet adhesion

Summary.  Background:  Type 2M von Willebrand disease (VWD) results from mutations in the A1 domain of von Willebrand factor (VWF) that reduce its platelet‐binding function. However, currently employed VWF functional static assays may not distinguish between clinical phenotype.

ADAMTS-13 glycans and conformation-dependent activity

Essentials The impact of N‐linked glycosylation on ADAMTS‐13 function has not been fully explored. The activity of glycan modified ADAMTS‐13 was investigated under static and shear stress conditions. Terminal sialic acid on the metalloprotease domain glycans are important for ADAMTS‐13 activity. The CUB domain glycans modulate ADAMTS‐13 activity.