Physiological and glycomic characterization of N-acetylglucosaminyltransferase-IVa and -IVb double deficient mice.

N-Acetylglucosaminyltransferase-IV (GnT-IV) has two isoenzymes, GnT-IVa and GnT-IVb, which initiate the GlcNAcbeta1-4 branch synthesis on the Manalpha1-3 arm of the N-glycan core thereby increasing N-glycan branch complexity and conferring endogenous lectin binding epitopes. To elucidate the physiological significance of GnT-IV, we engineered and characterized GnT-IVb-deficient mice and further generated GnT-IVa/-IVb double deficient mice. In wild-type mice, GnT-IVa expression is restricted to gastrointestinal tissues, whereas GnT-IVb is broadly expressed among organs.

Surfen, a small molecule antagonist of heparan sulfate.

In a search for small molecule antagonists of heparan sulfate, we examined the activity of bis-2-methyl-4-amino-quinolyl-6-carbamide, also known as surfen. Fluorescence-based titrations indicated that surfen bound to glycosaminoglycans, and the extent of binding increased according to charge density in the order heparin > dermatan sulfate > heparan sulfate > chondroitin sulfate. All charged groups in heparin (N-sulfates, O-sulfates, and carboxyl groups) contributed to binding, consistent with the idea that surfen interacted electrostatically.

The Ashwell receptor mitigates the lethal coagulopathy of sepsis.

The Ashwell receptor, the major lectin of hepatocytes, rapidly clears from blood circulation glycoproteins bearing glycan ligands that include galactose and N-acetylgalactosamine. This asialoglycoprotein receptor activity remains a key factor in the development and administration of glycoprotein pharmaceuticals, yet a biological purpose of the Ashwell receptor has remained elusive. We have identified endogenous ligands of the Ashwell receptor as glycoproteins and regulatory components in blood coagulation and thrombosis that include von Willebrand factor (vWF) and platelets.

Initiation of protein O glycosylation by the polypeptide GalNAcT-1 in vascular biology and humoral immunity.

Core-type protein O glycosylation is initiated by polypeptide N-acetylgalactosamine (GalNAc) transferase (ppGalNAcT) activity and produces the covalent linkage of serine and threonine residues of proteins. More than a dozen ppGalNAcTs operate within multicellular organisms, and they differ with respect to expression patterns and substrate selectivity. These distinctive features imply that each ppGalNAcT may differentially modulate regulatory processes in animal development, physiology, and perhaps disease.

Sialyltransferase ST3Gal-IV operates as a dominant modifier of hemostasis by concealing asialoglycoprotein receptor ligands.

A number of poorly characterized genetic modifiers contribute to the extensive variability of von Willebrand disease, the most prevalent bleeding disorder in humans. We find that a genetic lesion inactivating the murine ST3Gal-IV sialyltransferase causes a bleeding disorder associated with an autosomal dominant reduction in plasma von Willebrand factor (VWF) and an autosomal recessive thrombocytopenia. Although both ST3Gal-IV and ST6Gal-I sialyltransferases mask galactose linkages implicated as asialoglycoprotein receptor ligands, only ST3Gal-IV deficiency promotes asialoglycoprotein clearance mechanisms with a reduction in plasma levels of VWF and platelets.