The LEC11 Chinese hamster ovary mutant synthesizes N-linked carbohydrates containing sialylated, fucosylated lactosamine units. Analysis by one- and two-dimensional 1H NMR spectroscopy

Sialyl Lewis(x) hybridized complement receptor type 1 moderates acid aspiration injury

The potentially enhanced anti-inflammatory effects of the sialyl Lewis(x) (sLe(x))-decorated version of soluble complement receptor type 1 (sCR1) in moderating acid aspiration injury are examined. HCl was instilled in tracheostomy tubes placed in mice, and extravasation of (125)I-labeled albumin in bronchoalveolar lavage (BAL) fluid was used to calculate the vascular permeability index (PI). Neutrophil counts in BAL fluid and immunohistochemistry were performed. PI was moderated by 82% after treatment with sCR1sLe(x) compared with 54% in sCR1-untreated mice (P < 0.05). Respective reductions in PI in mice treated 0.5 and 1 h after acid aspiration with sCR1sLe(x) of 70 and 57% were greater than the decreases in PI of 45 and 38% observed in respective sCR1-treated groups (P < 0.05). BAL fluid neutrophil counts in sCR1sLe(x)-treated mice were significantly less than those in sCR1-treated animals, which were similar to those in untreated mice. Immunohistochemistry stained for sCR1 only on the pulmonary vascular endothelium of sCR1sLe(x)- but not sCR1-treated mice. In conclusion, sCR1sLe(x) moderates permeability by antagonizing complement activation and neutrophil adhesion. Delayed complement and neutrophil antagonism significantly reduces injury.

Moderation of skeletal muscle reperfusion injury by a sLe(x)-glycosylated complement inhibitory protein

The role of the sialyl Lewis(x) (sLe(x))-decorated version of soluble complement receptor type 1 (sCR1) in moderating skeletal muscle reperfusion injury, by antagonizing neutrophil endothelial selectin interaction and complement activation, is examined. Mice underwent 2 h of hindlimb ischemia and 3 h of reperfusion. Permeability index (PI) was assessed by extravasation of 125I-labeled albumin. Neutrophil depletion and complement inhibition with sCR1 reduced permeability by 72% (PI 0.81 +/- 0.10) compared with a 42% decrease (PI 1.53 +/- 0.08) observed in neutropenic mice, indicating that part of the complement-mediated injury is neutrophil independent. sCR1sLe(x) treatment reduced PI by 70% (PI 0.86 +/- 0.06), an additional 20% decrease compared with sCR1 treatment (PI 1.32 +/- 0.08). Treatment with sCR1sLe(x) 0.5 and 1 h after reperfusion reduced permeability by 63% (PI 0.09 +/- 0.07) and 52% (PI 1.24 +/- 0.09), respectively, compared with the respective decreases of 41% (PI 1.41 +/- 0.10) and 32% (PI 1.61 +/- 0.07) after sCR1 treatment. Muscle immunohistochemistry stained for sCR1 only on the vascular endothelium of sCR1sLe(x)-treated mice. In conclusion, sCR1sLe(x) is more effective than sCR1 in moderating skeletal muscle reperfusion injury.

The yeast ALG11 gene specifies addition of the terminal alpha 1,2-Man to the Man5GlcNAc2-PP-dolichol N-glycosylation intermediate formed on the cytosolic side of the endoplasmic reticulum

The initial steps in N-linked glycosylation involve the synthesis of a lipid-linked core oligosaccharide followed by the transfer of the core glycan to nascent polypeptides in the endoplasmic reticulum (ER). Here, we describe alg11, a new yeast glycosylation mutant that is defective in the last step of the synthesis of the Man(5)GlcNAc(2)-PP-dolichol core oligosaccharide on the cytosolic face of the ER. A deletion of the ALG11 gene leads to poor growth and temperature-sensitive lethality. In an alg11 lesion, both Man(3)GlcNAc(2)-PP-dolichol and Man(4)GlcNAc(2)-PP-dolichol are translocated into the ER lumen as substrates for the Man-P-dolichol-dependent sugar transferases in this compartment. This leads to a unique family of oligosaccharide structures lacking one or both of the lower arm alpha1,2-linked Man residues. The former are elongated to mannan, whereas the latter are poor substrates for outerchain initiation by Ochlp (Nakayama, K.-I., Nakanishi-Shindo, Y., Tanaka, A., Haga-Toda, Y., and Jigami, Y. (1997) FEBS Lett. 412, 547-550) and accumulate largely as truncated biosynthetic end products. The ALG11 gene is predicted to encode a 63.1-kDa membrane protein that by indirect immunofluorescence resides in the ER. The Alg11 protein is highly conserved, with homologs in fission yeast, worms, flies, and plants. In addition to these Alg11-related proteins, Alg11p is also similar to Alg2p, a protein that regulates the addition of the third mannose to the core oligosaccharide. All of these Alg11-related proteins share a 23-amino acid sequence that is found in over 60 proteins from bacteria to man whose function is in sugar metabolism, implicating this sequence as a potential sugar nucleotide binding motif.

The accumulation of Man(6)GlcNAc(2)-PP-dolichol in the Saccharomyces cerevisiae Deltaalg9 mutant reveals a regulatory role for the Alg3p alpha1,3-Man middle-arm addition in downstream oligosaccharide-lipid and glycoprotein glycan processing

N-Glycans in nearly all eukaryotes are derived by transfer of a precursor Glc(3)Man(9)GlcNAc(2) from dolichol (Dol) to consensus Asn residues in nascent proteins in the endoplasmic reticulum. The Saccharomyces cerevisiae alg (asparagine-linked glycosylation) mutants fail to synthesize oligosaccharide-lipid properly, and the alg9 mutant, accumulates Man(6)GlcNAc(2)-PP-Dol. High-field (1)H NMR and methylation analyses of Man(6)GlcNAc(2) released with peptide-N-glycosidase F from invertase secreted by Deltaalg9 yeast showed its structure to be Manalpha1,2Manalpha1,2Manalpha1, 3(Manalpha1,3Manalpha1,6)-Manbeta1,4GlcNAcbeta1, 4GlcNAcalpha/beta, confirming the addition of the alpha1,3-linked Man to Man(5)GlcNAc(2)-PP-Dol prior to the addition of the final upper-arm alpha1,6-linked Man. This Man(6)GlcNAc(2) is the endoglycosidase H-sensitive product of the Alg3p step. The Deltaalg9 Hex(7-10)GlcNAc(2) elongation intermediates were released from invertase and similarly analyzed. When compared with alg3 sec18 and wild-type core mannans, Deltaalg9 N-glycans reveal a regulatory role for the Alg3p-dependent alpha1,3-linked Man in subsequent oligosaccharide-lipid and glycoprotein glycan maturation. The presence of this Man appears to provide structural information potentiating the downstream action of the endoplasmic reticulum glucosyltransferases Alg6p, Alg8p and Alg10p, glucosidases Gls1p and Gls2p, and the Golgi Och1p outerchain alpha1,6-Man branch-initiating mannosyltransferase.

Endothelial Targeting and Enhanced Antiinflammatory Effects of Complement Inhibitors Possessing Sialyl Lewisx Moieties

The complement inhibitor soluble complement receptor type 1 (sCR1) and a truncated form of sCR1, sCR1[desLHR-A], have been generated with expression of the selectin-reactive oligosaccharide moiety, sialyl Lewisx (sLex), as N-linked oligosaccharide adducts. These modified proteins, sCR1sLex and sCR1[desLHR-A]sLex, were assessed in the L-selectin- and P-selectin-dependent rat model of lung injury following systemic activation of complement by cobra venom factor and in the L-selectin-, P-selectin-, and E-selectin-dependent model of lung injury following intrapulmonary deposition of IgG immune complexes. In the cobra venom factor model, sCR1sLex and sCR1[desLHR-A]sLex caused substantially greater reductions in neutrophil accumulation and in albumin extravasation in lung when compared with the non-sLex-decorated forms. In this model, increased lung vascular binding of sCR1sLex and sCR1[desLHR-A]sLex occurred in a P-selectin-dependent manner, in contrast to the absence of any increased binding of sCR1 or sCR1[desLHR-A]. In the IgG immune complex model, sCR1[desLHR-A]sLex possessed greater protective effects relative to sCR1[desLHR-A], based on albumin extravasation and neutrophil accumulation. Enhanced protective effects correlated with greater lung vascular binding of sCR1[desLHR-A]sLex as compared with the non-sLex-decorated form. In TNF-α-activated HUVEC, substantial in vitro binding occurred with sCR1[desLHR-A]sLex (but not with sCR1[desLHR-A]). This endothelial cell binding was blocked by anti-E-selectin but not by anti-P-selectin. These data suggest that sLex-decorated complement inhibitors have enhanced antiinflammatory effects and appear to have enhanced ability to localize to the activated vascular endothelium.

Expression of N-linked sialyl Le(x) determinants and O-glycans in the carbohydrate moiety of human amniotic fluid transferrin during pregnancy

Transferrin, a glycoprotein involved in iron transport in body fluids, was isolated from amniotic fluid of a hydramniospatient by sequential anion-exchange chromatography and gel filtration. The N-glycans of human amniotic fluid transferrin (hAFT) were enzymatically liberated by PNGase-F digestion, isolated by gel filtration and fractionated by (high-pH) anion-exchange chromatography. After alkaline borohydride treatment of native hAFT, the released O-glycans were isolated by gel filtration and fractionated by anion-exchange chroma-tography. Structure elucidation of 14 N- and 2 O-glycans was performed by 500 or 600 MHz1H-NMR spectroscopy. Besides conventional N-glycans established earlier for human serum transferrin (hST), new (alpha1-3)-fucosylated N-glycans were found, representing sialyl Le(x) elements. Furthermore, as compared to hST, a higher degree of (alpha1-6)-fucosylation and an increase in branching from di- to triantennary compounds has been detected. The presence of O-glycans is demonstrated for the first time in transferrin.

The E-selectin ligand-1 is selectively activated in Chinese hamster ovary cells by the alpha(1,3)-fucosyltransferases IV and VII

The E-selectin ligand-1 (ESL-1) has recently been identified as the major ligand on mouse neutrophils using a recombinant antibody-like form of E-selectin as affinity probe. The remarkable selectivity with which ESL-1 can be affinity-isolated is unexplained. Since ESL-1 is endogenously expressed in Chinese hamster ovary (CHO) cells in a non-E-selectin binding form, which can become activated upon transfection of a fucosyltransferase (FucT), we analyzed various CHO cell clones, each overexpressing one of seven different fucosyltransferases, by affinity isolation experiments with E-selectin-IgG. Two of the cell lines were the regulatory CHO mutants LEC11 and LEC12, each overexpressing a different hamster FucT, while the five other clones were stably transfected with human FucTIII to -VII. A large panel of glycoproteins was affinity-isolated with E-selectin-IgG from LEC11 cells and FucTIII transfectants, demonstrating that many different glycoproteins can acquire ligand activity upon alpha(1,3)-fucosylation. In contrast, ESL-1 was almost exclusively isolated as the dominant glycoprotein ligand from LEC12 cells as well as from FucTIV and FucTVII transfectants and less selectively from FucTV and FucTVI transfectants. The selective generation of ligand activity correlated with the selective generation of the HECA452-reactive carbohydrate epitope, which is known to bind to E-selectin. These data suggest that, dependent on the type of fucosyltransferase, ESL-1 is a strongly preferred target molecule for the generation of E-selectin-binding carbohydrate modifications.

ELAM-1 mediates cell adhesion by recognition of a carbohydrate ligand, sialyl-Lex

Recruitment of neutrophils to sites of inflammation is mediated in part by endothelial leukocyte adhesion molecule-1 (ELAM-1), which is expressed on activated endothelial cells of the blood vessel walls. ELAM-1 is a member of the LEC-CAM or selectin family of adhesion molecules that contain a lectin motif thought to recognize carbohydrate ligands. In this report, cell adhesion by ELAM-1 is shown to be mediated by a carbohydrate ligand, sialyl-Lewis X (SLex; NeuAc alpha 2,3Gal beta 1,4(Fuc alpha 1,3)-GlcNAc-), a terminal structure found on cell-surface glycoprotein and glycolipid carbohydrate groups of neutrophils.

Identification of mutations in the COL4A5 collagen gene in Alport syndrome

X-linked Alport syndrome is a hereditary glomerulonephritis in which progressive loss of kidney function is often accompanied by progressive loss of hearing. Ultrastructural defects in glomerular basement membranes (GBM) of Alport syndrome patients implicate an altered structural protein as the cause of nephritis. The product of COL4A5, the alpha 5(IV) collagen chain, is a specific component of GBM within the kidney, and the gene maps to the same X chromosomal region as does Alport syndrome. Three structural aberrations were found in COL4A5, in intragenic deletion, a Pst I site variant, and an uncharacterized abnormality, which appear to cause nephritis and deafness, with allele-specific severity, in three Alport syndrome kindreds in Utah.

Separation of fucosylated oligosaccharides using high-pH anion-exchange chromatography with pulsed-amperometric detection

Fucosylated oligosaccharides of the beta Gal(1----4)GlcNAc-, beta Gal(1----4)Glc-, and beta Gal(1----3)GlcNAc-series were chromatographed on a high-performance anion-exchange pellicular resin under alkaline conditions (pH congruent to 13). Fucosylation of either lactose, lactosamine (Type II chains), or lacto-N-biose (Type I chains) oligosaccharides markedly decreased the retention time (10-38 min) of the non-fucosylated form. The magnitude of the reduction was related to whether fucose replaced Gal [alpha Fuc(1----3)----GlcNAc], whether fucose was alpha-(1----2)-linked to Gal at the end of a chain, or whether fucose was linked in a subterminal position [alpha(1----3) or alpha (1----4)] to Gal or GlcNAc. The results suggest that the decreases in retention times of fucosylated oligosaccharides (10-38 min) is not attributable to the absence of a 6-OH in Fuc but instead to steric and substitution effects which affect the interaction of the most readily ionizable groups of Fuc (2-OH), Gal (2-OH), and GLcNAc (3-OH) with the stationary phase. We show that high-pH anion-exchange chromatography can effectively separate 1----2, 1----3, and 1----4 fucose positional isomers in a single chromatographic step.