Initiation of poly-N-acetyllactosamine chain biosynthesis occurs preferentially on complex multiantennary asparagine-linked oligosaccharides

Pompe disease results in a Golgi-based glycosylation deficit in human induced pluripotent stem cell-derived cardiomyocytes

Infantile-onset Pompe disease is an autosomal recessive disorder caused by the complete loss of lysosomal glycogen-hydrolyzing enzyme acid α-glucosidase (GAA) activity, which results in lysosomal glycogen accumulation and prominent cardiac and skeletal muscle pathology. The mechanism by which loss of GAA activity causes cardiomyopathy is poorly understood. We reprogrammed fibroblasts from patients with infantile-onset Pompe disease to generate induced pluripotent stem (iPS) cells that were differentiated to cardiomyocytes (iPSC-CM). Pompe iPSC-CMs had undetectable GAA activity and pathognomonic glycogen-filled lysosomes. Nonetheless, Pompe and control iPSC-CMs exhibited comparable contractile properties in engineered cardiac tissue. Impaired autophagy has been implicated in Pompe skeletal muscle; however, control and Pompe iPSC-CMs had comparable clearance rates of LC3-II-detected autophagosomes. Unexpectedly, the lysosome-associated membrane proteins, LAMP1 and LAMP2, from Pompe iPSC-CMs demonstrated higher electrophoretic mobility compared with control iPSC-CMs. Brefeldin A induced disruption of the Golgi in control iPSC-CMs reproduced the higher mobility forms of the LAMPs, suggesting that Pompe iPSC-CMs produce LAMPs lacking appropriate glycosylation. Isoelectric focusing studies revealed that LAMP2 has a more alkaline pI in Pompe compared with control iPSC-CMs due largely to hyposialylation. MALDI-TOF-MS analysis of N-linked glycans demonstrated reduced diversity of multiantennary structures and the major presence of a trimannose complex glycan precursor in Pompe iPSC-CMs. These data suggest that Pompe cardiomyopathy has a glycan processing abnormality and thus shares features with hypertrophic cardiomyopathies observed in the congenital disorders of glycosylation.

Generation of antibodies recognizing an aberrant glycoform of human tissue inhibitor of metalloproteinase-1 (TIMP-1) using decoy immunization and phage display

Aberrant glycosylation of human tissue inhibitor of metalloproteinase-1 (TIMP-1) by N-acetylglucosaminyltransferase-V (GnT-V) was previously reported to be related to cancer progression. Here, we report on the antibodies recognizing the structural features initiated by an addition of N-linked β(1,6)-N-acetylglucosamine (GlcNAc) branch by GnT-V on TIMP-1. Two glycoforms of TIMP-1, TIMP1-L produced in Lec4 cells without GnT-V activity and TIMP1-B in GnT-V overexpressing transfectant cells, were purified from culture supernatant and used for generation of antibodies. TIMP1-L was injected in the left hind footpad of mice as decoy and TIMP1-B in the right hind footpad as immunogen. Phage-displayed scFv library was constructed from the B cells retrieved from the right popliteal lymph nodes and subjected to panning and screening. Phage ELISA of individual clones revealed the scFv clones with preferential binding activity to TIMP1-B, and they were converted into an scFv-Fc format for further characterization of binding specificity. Glycan binding assay of an antibody, 1-9F, revealed its differential specificity toward an extension of glycan structure initiated with β(1,6)-GlcNAc linkage and terminally decorated with a sialic acid. This study demonstrates feasibility of a new strategy combining decoy immunization with phage display for the efficient generation of antibodies tracking down structural features of different glycoforms.

Polylactosamine on glycoproteins influences basal levels of lymphocyte and macrophage activation

beta1,3-N-acetylglucosaminyltransferase 2 (beta3GnT2) is a polylactosamine synthase that synthesizes a backbone structure of carbohydrate structures onto glycoproteins. Here we generated beta3GnT2-deficient (beta3GnT2(-/-)) mice and showed that polylactosamine on N-glycans was markedly reduced in their immunological tissues. In WT mice, polylactosamine was present on CD28 and CD19, both known immune costimulatory molecules. However, polylactosamine levels on these molecules were reduced in beta3GnT2(-/-) mice. beta3GnT2(-/-) T cells lacking polylactosamine were more sensitive to the induction of intracellular calcium flux on stimulation with anti-CD3epsilon/CD28 and proliferated more strongly than T cells from WT mice. beta3GnT2(-/-) B cells also showed hyperproliferation on BCR stimulation. Macrophages from beta3GnT2(-/-) mice had higher cell surface CD14 levels and enhanced responses to endotoxin. These results indicate that polylactosamine on N-glycans is a putative immune regulatory factor presumably suppressing excessive responses during immune reactions.

Structural characterization of oligosaccharides in recombinant soluble human interferon receptor 2 using fluorophore-assisted carbohydrate electrophoresis

The N-linked oligosaccharide profiles (banding patterns in gels) and structures of recombinant soluble human interferon receptor 2 (r-shIFNAR2) were determined using fluorophore-assisted carbohydrate electrophoresis (FACE, Glyko, Novato, CA). The method involves releasing N-linked oligosaccharide moieties from a glycoprotein by digestion with peptide-N glycanase (PNGase F), labeling the released oligosaccharides with the fluorescent dye 8-aminonaphthalene-1,3,6-trisulfonate (ANTS), and separating the labeled oligosaccharides by gel electrophoresis. The isolated oligosaccharides in the bands from the profiling gels can then be sequenced using exoglycosidases to reveal the oligosaccharide structures. The oligosaccharide profile of r-shIFNAR2 consists of at least nine oligosaccharide bands. The relative amount of oligosaccharide in each band can vary, depending on the culture conditions of the source cells. FACE structural analysis shows that r-shIFNAR2 contains only core-fucosylated N-linked oligosaccharides, most of which are fully sialylated (approximately 92%). The major types and relative amounts of the oligosaccharides from a representative sample are: disialylated, galactosylated, biantennary (15%); trisialylated, galactosylated, triantennary (19%), tetrasialylated, galactosylated, tetraantennary (30%), and N-acetyllactosamine-containing higher-order oligosaccharides including tri-, tetra-, and pentaantennary (28%). The remaining oligosaccharides are not fully sialylated and/or not fully galactosylated di-, tri-, and tetraantennary structures (approximately 5%) and unidentified structures (approximately 3%). A method for determining the types and structures of the N-acetyllactosamine containing oligosaccharides is also reported in this study.

Hydrophobic glycosides of N-acetylglucosamine can act as primers for polylactosamine synthesis and can affect glycolipid synthesis in vivo

Several hydrophobic glycosides of N-acetylglucosamine (GlcNAc) served as primers for polylactosamine synthesis when added to Chinese hamster ovary (CHO) cells. The modified glycosides, containing one to six lactosamine repeats in linear array, were sialylated and secreted into the culture medium. The relative efficiencies of the glycosides to serve as primers were dependent on the nature of the aglycone and on the anomeric configuration of the GlcNAc residue. The same compounds were tested for their effects on glycolipid synthesis in CHO cells. All of the beta-glycosides significantly inhibited the synthesis of the lactoseries glycolipid GM3 whereas the alpha-glycoside was inactive. The compound GlcNAc alpha 1-O-benzyl- was the most efficient primer of polylactosamine synthesis and had no effect on glycolipid synthesis. This compound may have potential for the assay of the polylactosamine synthetic capacity of living cells.

Characterization and direct glycoform profiling of a hybrid plasminogen activator by matrix-assisted laser desorption and electrospray mass spectrometry: correlation with high-performance liquid chromatographic and nuclear magnetic resonance analyses of the released glycans

Mass spectrometric analysis of the recombinant hybrid plasminogen activator K2tu-PA at the native glycoprotein and corresponding protein level (high mass) is described. For gross structural characterization of the major glycotypes present, a combination of enzymatic degradation and matrix-assisted laser desorption mass spectrometric analysis of the products proved convenient. In this way, mono- and di-N-glycosylated one- and two-chain molecules, unresolved in the spectra of native material, were identified, with the one-chain type monoglycosylated at Asn247 representing the major component. Actual detection of resolved original glycoforms, or unresolved groups thereof when composed of isobaric species, and their assignments regarding antennicity and degree of sialylation were possible by electrospray mass spectrometry for the major monoglycosylated one-chain species. Desialation also allowed detection of the diglycosylated one-chain species as a minor constituent. The electrospray mass spectrometric results were correlated with structural and quantitative data available from a parallel high-performance liquid chromatographic and 1H nuclear magnetic resonance study performed at the glycan (low mass) level on liberated individual carbohydrate components. The results of the two studies showed full consistency in all respects amenable to evaluation, i.e. excellent agreement for the assignments of antennicity and degree of sialylation of the major glycan components, and good agreement for the determination of proportions in which these were present in the major monoglycosylated glycoprotein. This provided a sound basis for direct glycoform profiling by electrospray mass spectrometry. Typical applications to batch quality control and to structural characterization of non-standard material are shown.

Synthesis of a tetrasaccharide acceptor for use in the assay of UDP-GlcpNAc:beta-D-Galp-(1----4)-beta-D-GlcpNAc (GlcNAc to Gal) beta(1----3)-N-acetylglucosaminyltransferase activity and the pentasaccharide product that would be formed by its enzymic glycosylation

The tetrasaccharide beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----6)-alpha-D- Manp-(1----6)-beta-D-Manp-OR (2) and the pentasaccharide beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-beta-D- GlcpNAc-(1----6)-alpha-D-Manp-(1----6)-beta-D-Manp-OR (3), where R = (CH2)8COOMe, have been prepared by using combined chemical and enzymic procedures. Structure 2 is a substrate for UDP-GlcpNAc:beta-D-Galp-(1----4)- beta-D-GlcpNAc (GlcNAc to Gal) beta(1----3)-N-acetylglucosaminyltransferase, and 3 would be the product of its action. Antibodies raised against 3 are intended for use in an ELISA assay that would quantitate the enzymic conversion of immobilized 2 into 3.