The glycan-specific sulfotransferase (R77W)GalNAc-4-ST1 putatively responsible for peeling skin syndrome has normal properties consistent with a simple sequence polymorphisim.

Expanded access to DNA sequencing now fosters ready detection of site-specific human genome alterations whose actual significance requires in-depth functional study to rule in or out disease-causing mutations. This is a particular concern for genomic sequence differences in glycosyltransferases, whose implications are often difficult to assess. A recent whole-exome sequencing study identifies (c.

Functional Consequences of Mannose and Asialoglycoprotein Receptor Ablation.

The mannose receptor (ManR, Mrc1) and asialoglycoprotein receptor (ASGR, Asgr1 and Asgr2) are highly abundant endocytic receptors expressed by sinusoidal endothelial cells and parenchymal cells in the liver, respectively. We genetically manipulated either receptor individually or in combination, revealing phenotypic changes in female and male mice associated with changes in circulating levels of many glycoproteins. Both receptors rise and fall in response to progesterone during pregnancy.

Modulation of mannose and asialoglycoprotein receptor expression determines glycoprotein hormone half-life at critical points in the reproductive cycle.

The rate at which glycoproteins are cleared from the circulation has a critical impact on their biologic activity in vivo. We have shown that clearance rates for glycoproteins such as luteinizing hormone (LH) that undergo regulated release into the circulation determine their potency. Two highly abundant, carbohydrate-specific, endocytic receptors, the asialoglycoprotein receptor (ASGR) and the mannose receptor (ManR) are expressed in the liver by parenchymal and sinusoidal endothelial cells, respectively.

Peptide-specific transfer of N-acetylgalactosamine to O-linked glycans by the glycosyltransferases β1,4-N-acetylgalactosaminyl transferase 3 (β4GalNAc-T3) and β4GalNAc-T4.

N- and O-linked oligosaccharides on pro-opiomelanocortin both bear the unique terminal sequence SO(4)-4-GalNAcβ1,4GlcNAcβ. We previously demonstrated that protein-specific transfer of GalNAc to N-linked oligosaccharides on glycoprotein substrates is dependent on the presence of both an oligosaccharide acceptor and a peptide recognition motif consisting of a cluster of basic amino acids. We characterized how two β1,4-N-acetylgalactosaminyltransferases, β4GalNAc-T3 and β4GalNAc-T4, require the presence of both the peptide recognition motif and the N-linked oligosaccharide acceptors to transfer GalNAc in β1,4-linkage to GlcNAc in vivo and in vitro.

Molecular basis for protein-specific transfer of N-acetylgalactosamine to N-linked glycans by the glycosyltransferases β1,4-N-acetylgalactosaminyl transferase 3 (β4GalNAc-T3) and β4GalNAc-T4.

Two closely related β1,4-N-acetylgalactosaminyltransferases, β4GalNAc-T3 and β4GalNAc-T4, are thought to account for the protein-specific addition of β1,4-linked GalNAc to Asn-linked oligosaccharides on a number of glycoproteins including the glycoprotein hormone luteinizing hormone and carbonic anhydrase-6 (CA6). We have utilized soluble, secreted forms of β4GalNAc-T3 and β4GalNAc-T4 to define the basis for protein-specific GalNAc transfer in vitro to chimeric substrates consisting of Gaussia luciferase followed by a glycoprotein substrate. Transfer of GalNAc by β4GalNAc-T3 and β4GalNAc-T4 to terminal GlcNAc is divalent cation-dependent.

Ablation of GalNAc-4-sulfotransferase-1 enhances reproduction by altering the carbohydrate structures of luteinizing hormone in mice.

Luteinizing hormone (LH), produced in the anterior lobe of the pituitary, is a member of the hypothalamic-pituitary-gonad axis that is required for production of the sex hormones estradiol, progesterone, and testosterone. Perturbations in levels of hormones associated with this axis can result in defects in sexual development and maturity. LH bears unique N-linked carbohydrate units that terminate with a sulfated N-acetylgalactosamine structure (GalNAc-4-SO(4)) that mediates its clearance from the blood.

A necessary and sufficient determinant for protein-selective glycosylation in vivo.

A limited number of glycoproteins including luteinizing hormone and carbonic anhydrase-VI (CA6) bear N-linked oligosaccharides that are modified with beta1,4-linked N-acetylgalactosamine (GalNAc). The selective addition of GalNAc to these glycoproteins requires that the beta1,4-N-acetylgalactosaminyltransferase (betaGT) recognize both the oligosaccharide acceptor and a peptide recognition determinant on the substrate glycoprotein. We report here that two recently cloned betaGTs, betaGT3 and betaGT4, that are able to transfer GalNAc to GlcNAc in beta1,4-linkage display the necessary glycoprotein specificity in vivo.

N-linked oligosaccharides on the low density lipoprotein receptor homolog SorLA/LR11 are modified with terminal GalNAc-4-SO4 in kidney and brain.

Sorting protein-related receptor (SorLA/LR11) is a highly conserved mosaic receptor that is expressed by cells in a number of different tissues including principal cells of the collecting ducts in the kidney and neurons in the central and peripheral nervous systems. SorLA/LR11 has features that indicate it serves as a sorting receptor shuttling between the plasma membrane, endosomes, and the Golgi. We have found that a fraction of SorLA/LR11 that is synthesized in the kidney and the brain bears N-linked oligosaccharides that are modified with terminal beta1,4-linked GalNAc-4-SO(4).

Neuronal-specific synthesis and glycosylation of tenascin-R.

Tenascin-R (TN-R) is a member of the tenascin family of multidomain matrix glycoproteins that is expressed exclusively in the central nervous system by oligodendrocytes and small neurons during postnatal development and in the adult. TN-R contributes to the regulation of axon extension and regeneration, neurite formation and synaptogenesis, and neuronal growth and migration. TN-R can be modified with three distinct sulfated oligosaccharide structures: HNK-1 (SO(4)-3-GlcUAbeta1,3Galbeta1,4GlcNAc), GalNAc-4-SO(4), and chondroitin sulfate.

Spatial and temporal regulation of tenascin-R glycosylation in the cerebellum.

The cellular adhesion molecule tenascin-R is a multifunctional extracellular matrix component expressed exclusively in the central nervous system. The expression of tenascin-R by oligodendrocytes and small interneurons in the hippocampus and cerebellum is highly regulated during development of these regions. This complex glycoprotein displays both adhesive and anti-adhesive properties that contribute to the formation and maintenance of synapses.