Isolation and characterisation of glycopeptides from digests of human Tamm-Horsfall glycoprotein

Tamm-Horsfall Protein is a Potent Immunomodulatory Molecule and a Disease Biomarker in the Urinary System

Tamm–Horsfall protein (THP), or uromodulin (UMOD), is an 80–90-kDa phosphatidylinositol-anchored glycoprotein produced exclusively by the renal tubular cells in the thick ascending limb of the loop of Henle. Physiologically, THP is implicated in renal countercurrent gradient formation, sodium homeostasis, blood pressure regulation, and a defense molecule against infections in the urinary system. Investigations have also revealed that THP is an effective binding ligand for serum albumin, immunoglobulin G light chains, complement components C1 and C1q, interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF)-α, and interferon-γ through its carbohydrate side chains for maintaining circulatory and renal immune homeostasis. Thus, THP can be regarded as part of the innate immune system. UMOD mutations play crucial roles in congenital urolithiasis, hereditary hyperuricemia/gout, and medullary cystic kidney diseases. Recent investigations have focused on the immunomodulatory effects of THP on immune cells and on THP as a disease biomarker of acute and chronic kidney diseases. Our studies have suggested that normal urinary THP, through its epidermal growth factor (EGF)-like domains, binds to the surface-expressed EGF-like receptors, cathepsin G, or lactoferrin to enhance polymorphonuclear leukocyte phagocytosis, proinflammatory cytokine production by monocytes/macrophages, and lymphocyte proliferation by activating the Rho family and mitogen-activated protein kinase signaling pathways. Furthermore, our data support both an intact protein core structure and carbohydrate side chains are important for the different protein-binding capacities of THP. Prospectively, parts of the whole THP molecule may be used for anti-TNF-α therapy in inflammatory diseases, autoantibody-depleting therapy in autoimmune disorders, and immune intensification in immunocompromised hosts.

Tamm-Horsfall glycoprotein enhances PMN phagocytosis by binding to cell surface-expressed lactoferrin and cathepsin G that activates MAP kinase pathway

The molecular basis of polymorphonuclear neutrophil (PMN) phagocytosis-enhancing activity (PEA) by human purified urinary Tamm-Horsfall glyco- protein (THP) has not been elucidated. In this study, we found human THP bound to lactoferrin (LF) and cathepsin G (CG) expressed on the surface of PMN, identified by a proteomic study with MALDI-TOF- LC/LC/mass spectrometric analysis. Pre-incubation of 10% SDS-PAGE electrophoresed PMN lysates with monoclonal anti-LF or anti-CG antibody reduced the binding with THP. To elucidate the signaling pathway of THP on PMN activation, we found THP enhanced ERK1/2 phosphorylation, reduced p38 MAP kinase phosphorylation, but had no effect on DNA binding of the five NF-kB family members in PMN. To further clarify whether the carbohydrate-side chains or protein-core structure in THP molecule is responsible for THP-PEA, THP was cleaved by different degrading enzymes with carbohydrate specificity (neuraminidase and β-galactosidase), protein specificity (V8 protease and proteinase K) or glycoconjugate specificity (carboxylpeptidase Y and O-sialoglycoprotein endopeptidase). We clearly demonstrated that the intact protein-core structure in THP molecule was more important for THP-PEA than carbohydrate-side chains. Putting these results together, we conclude that THP adheres to surface-expressed LF and CG on PMN and transduces signaling via the MAP kinase pathway to enhance PMN phagocytosis.

Intact protein core structure is essential for protein-binding, mononuclear cell proliferating, and neutrophil phagocytosis-enhancing activities of normal human urinary Tamm-Horsfall glycoprotein

Tamm-Horsfall glycoprotein (THP) is synthesized in the particular sites of renal tubules acting as a defense molecule in the urinary system. In the present study, we found that THP contained high amount of Siaalpha(2,3)Gal/GalNAc, moderate amount of beta(1,4)GlcNAc oligomers and GlcNAc/branched mannose, and low amount of mannose residues, but no Siaalpha(2,6)Gal/GalNAc, in the side-chains of the molecule. THP exhibited high binding affinity with human TNF-alpha, IgG, C1q and BSA, moderate binding affinity with IL-8, and low binding affinity with IL-6 and IFN-gamma. For exploring the role of carbohydrate side-chains and protein core in the protein-binding and cell-stimulating activities, THP was enzyme-digested with carbohydrate-specific [neuraminidase (Nase), beta-galactosidase (Gase)], protein-specific [V8 protease (V8), proteinase K (PaseK)] and glycoconjugate-specific [carboxypeptidase Y (Case), O-sialoglycoprotein endopeptidase (Oase)] degrading enzymes. We found that THP digested with V8, Oase, and PaseK, significantly reduced its protein-binding, mononuclear cell proliferating, and neutrophil phagocytosis-enhancing activities. These results suggest that the intact protein core structure, but not carbohydrate side-chains, is essential for pleotropic functions of THP molecule.

Immunological evaluation of urinary trypsin inhibitors in blood and urine: role of N- & O-linked glycoproteins

Urinary trypsin inhibitors (uTi) suppress serine proteases during inflammation. After liberation from proinhibitors (P-alpha-I and I-alpha-I) by the white blood cell (WBC) response, uTi readily pass through the kidneys into urine. A key uTi, bikunin, is attached to O-linked and N-linked glycoconjugates. Recently, uTi inhibitors, called uristatins, were found to lack the O-linked glycoconjugates. Monoclonal antibodies were produced using purified uristatin and screened for binding differences to uristatin, bikunin, P-alpha-I, and I-alpha-I. Antibody-binding patterns were characterized using immunoaffinity binding onto protein-chip surfaces and analysis by Surface Enhanced Laser Desorption/Ionization mass spectrometry (SELDI), using specimens from patients and from purified uTi standards. Antibodies were developed and used in an enzyme-linked immunosorbent assay (ELISA) method for uTi measurement in urine and plasma specimens. ELISA was performed on specimens from normal, presumed healthy, controls and from patients who had been screened for inflammation using a high sensitivity C-reactive protein (CRP) test and a complete blood count (CBC). Polyclonal antibody against uTi showed cross-reactivity with the Tamm-Horsfall protein (THP) and with proinhibitors. Screening of anti-uTi monoclonal antibodies (Mab) revealed antibodies that did not cross-react with either of the above, thus providing a tool to measure both uristatin and bikunin in urine with Mab 3G5 and in plasma with Mab 5D11. The monoclonal antibody 5D11 cross-reacts with specific N-linked glycoconjugates of uristatin present in plasma. In ca 96% of healthy adults, uTi were present at <12 mg/l in urine and <4 mg/l in plasma. We also found that patients with an inflammation and a CRP of >2.0 mg/l had higher urinary concentrations of uTi than the control population in every subject. Free uristatin and bikunin pass readily into urine and are primarily bound to heavy chains that constitute the proinhibitor form in plasma.

In vitro sulfation of N-acetyllactosaminide by soluble recombinant human β-Gal-3′-sulfotransferase

Membrane-bound beta-Gal-3'-sulfotransferase (GP3ST) was expressed and used for in vitro sulfation of Tamm-Horsfall glycoprotein. Further, the regioselective transfer of sulfate to an N-acetyllactosamine derivative could be realised with soluble chimeric GP3ST, also in combination with Lac transglycosylation by means of beta-galactosidase. Two alternative straightforward chemical syntheses for the target compound could be elaborated.

Tamm-Horsfall glycoprotein: biology and clinical relevance

Tamm-Horsfall glycoprotein (THP) is the most abundant urinary protein in mammals. Urinary excretion occurs by proteolytic cleavage of the large ectodomain of the glycosyl phosphatidylinositol-anchored counterpart exposed at the luminal cell surface of the thick ascending limb of Henle's loop. We describe the physical-chemical structure of human THP and its biosynthesis and interaction with other proteins and leukocytes. The clinical relevance of THP reported here includes: (1) involvement in the pathogenesis of cast nephropathy, urolithiasis, and tubulointerstitial nephritis; (2) abnormalities in urinary excretion in renal diseases; and (3) the recent finding that familial juvenile hyperuricemic nephropathy and autosomal dominant medullary cystic kidney disease 2 arise from mutations of the THP gene. We critically examine the literature on the physiological role and mechanism(s) that promote urinary excretion of THP. Some lines of research deal with the in vitro immunoregulatory activity of THP, termed uromodulin when isolated from urine of pregnant women. However, an immunoregulatory function in vivo has not yet been established. In the most recent literature, there is renewed interest in the capacity of urinary THP to compete efficiently with urothelial cell receptors, such as uroplakins, in adhering to type 1 fimbriated Escherichia coli. This property supports the notion that abundant THP excretion in urine is promoted in the host by selective pressure to obtain an efficient defense against urinary tract infections caused by uropathogenic bacteria.

The patterns of the complex- and oligomannose-type glycans of uromodulin (Tamm-Horsfall glycoprotein) in the course of pregnancy

Uromodulin was isolated from urine of three pregnant women. Urine of each donor was collected at subsequent stages of their pregnancy and at one month after gestation. Each batch of uromodulin was enzymatically N-deglycosylated and the released N-glycans were isolated, quantified and profiled by high-pH anion-exchange chromatography. In the course of pregnancy no significant changes were detected in the negative charge distribution stemming from sialic acid and sulfate residues on the complex-type carbohydrate chains of uromodulin. Furthermore, no significant changes in the molar ratio between Man6GlcNAc2 and Man7GlcNAc2 were found in the course of pregnancy, only uromodulin from non-pregnant periods showed small differences.

Tamm-Horsfall protein binds to type 1 fimbriated Escherichia coli and prevents E. coli from binding to uroplakin Ia and Ib receptors

The adherence of uropathogenic Escherichia coli to the urothelial surface, a critical first step in the pathogenesis of urinary tract infection (UTI), is controlled by three key elements: E. coli adhesins, host receptors, and host defense mechanisms. Although much has been learned about E. coli adhesins and their urothelial receptors, little is known about the role of host defense in the adherence process. Here we show that Tamm-Horsfall protein (THP) is the principal urinary protein that binds specifically to type 1 fimbriated E. coli, the main cause of UTI. The binding was highly specific and saturable and could be inhibited by d-mannose and abolished by endoglycosidase H treatment of THP, suggesting that the binding is mediated by the high-mannose moieties of THP. It is species-conserved, occurring in both human and mouse THPs. In addition, the binding to THP was much greater with an E. coli strain bearing a phenotypic variant of the type 1 fimbrial FimH adhesin characteristic of those prevalent in UTI isolates compared with the one prevalent in isolates from the large intestine of healthy individuals. Finally, a physiological concentration of THP completely abolished the binding of type 1 fimbriated E. coli to uroplakins Ia and Ib, two putative urothelial receptors for type 1 fimbriae. These results establish, on a functional level, that THP contains conserved high-mannose moieties capable of specific interaction with type 1 fimbriae and strongly suggest that this major urinary glycoprotein is a key urinary anti-adherence factor serving to prevent type 1 fimbriated E. coli from binding to the urothelial receptors.

Role of polymeric Tamm-Horsfall protein in cast formation: oligosaccharide and tubular fluid ions

BACKGROUND

In acute tubular necrosis (ATN), distal tubules are obstructed by casts formed by tubular debris, cells, and Tamm-Horsfall protein (THP). Since there are Arginine-Glycine-Aspartate (RGD) and Leucine-Aspartate-Valine (LDV) adhesive sequences in human THP, there may be direct integrin-mediated binding of tubular cells to THP. Alternatively, polymerization of THP may result in entrapment of the cells in its gel.

METHODS

Adhesion of LLC-PK(1) cells to THP-coated wells was directly measured. THP concentrate was dissolved in solutions which mimic urine from ATN (ATN-S), distal convoluted tubule (DCT-S), collecting duct (CD-S), and monomeric buffer (M buffer). THP was also denatured by either boiling or N-glycanase digestion. Gel formation of THP was then measured. Inhibition of LLC-PK(1) cell adhesion to collagen type I was measured with each solution, as well as after the collagen was pretreated with either monomeric (mTHP) or polymeric (pTHP) THP. The effect of pTHP on the settling rate of LLC-PK(1) cells in suspension was also measured.

RESULTS

LLC-PK(1) cells did not directly adhere to THP, a finding against integrin-mediated binding as a mechanism for in vivo tubular cell/THP cast formation. The high electrolyte concentration of ATN-S and CD-S, however, was associated with pTHP gel formation. Moreover, cells suspended in pTHP remained in suspension. In cell adhesion studies, mTHP attenuated cell adhesion by binding to the matrix, whereas pTHP attenuated cell adhesion by trapping cells in its gel. An active process was involved since both pTHP gel formation and attenuation of cell adhesion were abolished by boiling or oligosaccharide removal with N-glycanase digestion.

CONCLUSIONS

With renal ischemia and proximal tubule cell shedding, ATN and collecting duct fluid composition enhance THP gel formation and thus favor tubular cast formation and obstruction. The present in vitro results indicate the importance of oligosaccharide residues in mediating the effect of the THP on gel formation and potential cast formation in ATN.

Pregnancy-associated changes in the glycosylation of tamm-horsfall glycoprotein. Expression of sialyl Lewis(x) sequences on core 2 type O-glycans derived from uromodulin

Tamm-Horsfall glycoprotein (THP) is a major glycoprotein associated with human urine that binds pro-inflammatory cytokines and also inhibits in vitro T cell proliferation induced by specific antigens. THP derived from human pregnancy urine (designated uromodulin) has previously been shown to be 13-fold more effective as an inhibitor of antigen-induced T cell proliferation than THP obtained from other sources. Structural analysis of human THP and uromodulin has for the first time revealed that these glycoproteins are O-glycosylated. THP from nonpregnant females and males expresses primarily core 1 type O-glycans terminated with either sialic acid or fucose but not the sialyl Lewis(x) epitope. By contrast, the O-glycans linked to uromodulin include unusual core 2 type glycans terminated with one, two, or three sialyl Lewis(x) sequences. The specific association of these unusual carbohydrate sequences with uromodulin could explain its enhanced immunomodulatory effects compared with THP obtained from males and nonpregnant females. Analysis of THP from one of the pregnant females 2 months postpartum showed a reversion of the O-glycan profile to that found for a non-pregnant female. These data suggest that the glycosylation state of uromodulin could be under the regulation of steroidal hormones produced during pregnancy. The significant physiological implications of these observations are discussed.

Glycosylation sites and site-specific glycosylation in human Tamm-Horsfall glycoprotein

The N-glycosylation sites of human Tamm-Horsfall glycoprotein from one healthy male donor have been characterized, based on an approach using endoproteinase Glu-C (V-8 protease, Staphylococcus aureus ) digestion and a combination of chromatographic techniques, automated Edman sequencing, and fast atom bombardment mass spectrometry. Seven out of the eight potential N-glycosylation sites, namely, Asn52, Asn56, Asn208, Asn251, Asn298, Asn372, and Asn489, turned out to be glycosylated, and the potential glycosylation site at Asn14, being close to the N-terminus, is not used. The carbohydrate microheterogeneity on three of the glycosylation sites was studied in more detail by high-pH anion-exchange chromatographic profiling and 500 MHz1H-NMR spectroscopy. Glycosylation site Asn489 contains mainly di- and tri-charged oligosaccharides which comprise, among others, the GalNAc4 S (beta1-4)GlcNAc terminal sequence. Only glycosylation site Asn251 bears oligomannose-type carbohydrate chains ranging from Man5GlcNAc2to Man8GlcNAc2, in addition to a small amount of complex-type structures. Profiling of the carbohydrate moieties of Asn208 indicates a large heterogeneity, similar to that established for native human Tamm-Horsfall glycoprotein, namely, multiply charged complex-type carbohydrate structures, terminated by sulfate groups, sialic acid residues, and/or the Sda-determinant.

Synthesis of the Sda determinant and two analogous tetrasaccharides

To contribute to the possibility of studying in greater detail the biological significance of Sda-containing glycans as occur in Tamm-Horsfall glycoprotein, the following three spacer-linked tetrasaccharides have been synthesized: the Sda determinant alpha-Neu p5Ac-(2-->3)-[beta- D-GalpNAc-(1-->4)]-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->O)(CH2)5NH 2 (1), the Gal-analogue alpha-Neup5Ac-(2-->3)-[beta-D-Galp-(1-->4)]-beta-D-Galp-(1-->4) -beta-D-GlcpNAc-(1-->O)(CH2)5NH2 (2), and the GlcNAc-analogue alpha-Neup5Ac-(2-->3)-[beta-D-GlcpNAc-(1-->4)]- beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->O)(CH2)5NH2 (3). The general trisaccharide acceptor 5-azidopentyl (methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy- D-glycero-alpha-D-galactonon-2-ulopyranosylonate)-(2-->3)-(2 ,6-di-O-benzyl- beta-D-galactopyranosyl)-(1-->4)-3,6-di-O- benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside was prepared, using methyl (phenyl 5- acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-D-galacto- non- 2-ulopyranosid)- onate as the sialyl donor. For the syntheses of 1, 2, and 3 the glycosyl donors 3,4,6-tri-O- acetyl-2-deoxy-2-phthalimido-alpha-D-galactopyranosyl bromide, 2,3,4,6-tetra-O-acetyl-alpha-D- galactopyranosyl bromide, and 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido -beta-D-glucopyranosyl trichloroacetimidate, respectively, proved to be the most suitable.

The Asn-linked carbohydrate chains of human Tamm-Horsfall glycoprotein of one male. Novel sulfated and novel N-acetylgalactosamine-containing N-linked carbohydrate chains

Human Tamm-Horsfall glycoprotein has been purified from the urine of one male. The Asn-linked carbohydrate chains were enzymically released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F, and separated from the remaining protein by gel-permeation chromatography on Bio-Gel P-100. Fractionation of the intact (sulfated) sialylated carbohydrate chains was achieved by a combination of three liquid-chromatographic techniques, namely, anion-exchange FPLC on Q-Sepharose, amine-adsorption HPLC on Lichrospher-NH2, and high-pH anion-exchange chromatography on CarboPac PA1. In total, more than 150 carbohydrate-containing fractions were obtained, some of which still contained mixtures of oligosaccharides. The primary structure of 30 N-glycans, including 10 novel oligosaccharides, were determined by one- and two-dimensional 1H-NMR spectroscopy at 500 MHz or 600 MHz. The types of compounds identified range from non-fucosylated, monosialylated, diantennary to fucosylated, tetrasialylated, tetraantennary carbohydrate chains, possessing the following terminal structural elements: [formula: see text]

Urinary Tamm-Horsfall glycoprotein concentrations in normal and urolithiasis-affected male cats determined by an ELISA

A precise and reproducible enzyme-linked immunosorbent assay (ELISA) which measures urinary cat Tamm-Horsfall glycoprotein (cTHP) was developed in order to investigate the possible role of cTHP in the pathogenesis of feline urolithiasis. Reproducible quantification required that the cTHP be disaggregated with 2M urea and 0.05% Tween 20. It was necessary to standardize rigidly the handling of the samples prior to analysis, since the apparent cTHP concentration varied depending on the preanalysis protocols. Using the sample handling protocol of freezing urine at -70 degrees C before dialysis, urinary cTHP was quantified in male cats with no history of urolithiasis ("normal" cats) and in male cats with a history of urolith formation ("urolithiasis" cats). The mean cTHP concentration in adult, male "normal" cats of 49.2 +/- 35.5 micrograms/ml (N = 23) was significantly lower than the mean cTHP concentration of 95.4 +/- 34.1 micrograms/ml (N = 9) in "urolithiasis" cats (p < 0.01, Students' T-test). These findings indicate a correlation between urolithiasis and high urine cTHP concentrations in male cats which warrants further investigation.

Pregnancy-associated changes in oligomannose oligosaccharides of human and bovine uromodulin (Tamm-Horsfall glycoprotein)

The urinary glycoprotein uromodulin (Tamm-Horsfall glycoprotein) exhibits a pregnancy-associated ability to inhibit antigen-specific T cell proliferation, and the activity is associated with a carbohydrate moiety [Muchmore and Decker (1985) Science 229:479-81; Hession et al., (1987) Science 237:1479-84; Muchmore, Shifrin and Decker (1987) J Immunol 138:2547-53]. We report here that the Man6(7)GlcNAc2-R glycopeptides derived from uromodulin inhibit antigen-specific T cell proliferation by 50% at 0.2-2 microM, and further studies, reported elsewhere, confirm that oligomannose glycopeptides from other sources are also inhibitory, with Man9GlcNAc2-R the most inhibitory of those tested [Muchmore et al., J Leukocyte Biol (in press)]. In this work, we have extended the observation of pregnancy-associated inhibitory activity to a second species, and have compared the oligomannose profile of Tamm-Horsfall glycoprotein (nonpregnant) with that of uromodulin (pregnant) derived from both human and bovine sources. Surprisingly, there was a pregnancy-associated decrease in the total content of oligomannose chains due predominantly to a reduction in Man5GlcNAc2-R and Man6GlcNAc2-R. Man7GlcNAc2-R, which did not decrease with pregnancy, comprised a significantly greater proportion of the total oligomannose chains in pregnant vs. nonpregnant samples from both species (human; 34.6% vs. 25.9%: bovine; 14.4% vs. 7.2%).

Activation of the inflammatory response of neutrophils by Tamm-Horsfall glycoprotein

The activation of human polymorphonuclear leukocytes (PMN) by particulate Tamm-Horsfall glycoprotein (THG) represents an interaction hitherto unrecognized. The potential pathophysiological effect of this phenomenon within the interstitium of the kidney is highlighted by the activation of the respiratory burst, as well as by comprehensive PMN degranulation. Products of the interaction are expressed in terms of phagocytosis, luminol-dependent chemiluminescence, granule marker enzyme release and arachidonic acid metabolism. Significant quantities of the primary, secondary and tertiary granule markers, myeloperoxidase, vitamin B12 binding protein and N-acetyl-beta-D-glucosaminidase, respectively, were secreted in a dose and time-dependent manner. Phagocytosis of the glycoprotein was accompanied by the generation of significant quantities of leukotriene B4. Furthermore, the ability of such a particulate ligand to activate the alternative pathway of complement clearly represents a capacity to augment the inflammatory response. Should the interaction of THG with PMN take place within the interstitium of the kidney, augmented by the deposition of complement proteins on the surface of insoluble aggregates, the resulting inflammatory response may lead to marked tissue damage and eventually result in interstitial fibrosis.

Characterization of N-acetyl-beta-D-galactosaminyltransferase from guinea-pig kidney involved in the biosynthesis of Sda antigen associated with Tamm-Horsfall glycoprotein

This study reports the catalytic activity of N-acetyl-beta-D-galactosaminyltransferase from guinea-pig kidney towards such non-glycoprotein acceptors as small oligosaccharides and glycolipids, having a carbohydrate structure similar to that of the Sda antigen associated with human Tamm-Horsfall glycoprotein. 3'-O-Sialyllactose, but not 6'-O-sialyllactose or lactose, was an effective acceptor of the glycosyltransferase. On the basis of enzymic and chemical treatment of the tetrasaccharide obtained by the transfer of [14C]GalNAc to 3'-O-sialyllactose, we propose that the glycosyltransferase attaches beta-D-GalNAc to O-4 of the galactose residue that is substituted at O-3 by sialic acid. The GM3 ganglioside, in which the identical carbohydrate moiety of 3'-O-sialyllactose is bound to a ceramide residue, did not serve as an acceptor of the kidney-N-acetyl-beta-D-galactosaminyltransferase and did not behave as a competitive inhibitor of the Tamm-Horsfall glycoprotein in the transferase assay. These results indicate that the hydrophobic moiety in the ganglioside hinders the action of N-acetylgalactosaminyltransferase. Study of the transferase activity towards a heterogeneous glycopeptide species prepared from a Sd(a-) Tamm-Horsfall glycoprotein indicated that guinea-pig kidney enzyme preferentially transferred [14C]GalNAc to the oligosaccharides having a tetraantennary branching-structure.

Structural analysis of the carbohydrate moieties of human Tamm-Horsfall glycoprotein

Glycopeptides present in a pronase digest of human Tamm-Horsfall glycoprotein were fractionated by chromatography on DEAE-Sephadex A25 in 0.1M acetic acid. The separated glycopeptides were characterised by 500-MHz 1H-n.m.r. spectroscopy, in conjunction with sugar and amino acid analysis, and they were shown to be of the N-glycosylic, N-acetyllactosamine type. Each fraction consisted mainly of a tetra-antennary entity having various degrees of complexity, with lesser amounts of the triantennary structure, and even smaller amounts of the diantennary type. There was extensive heterogeneity in non-reducing terminal groups in each of the glycopeptides, whereas the peptide portions were similar. The extent to which any one of the galactose residues in the N-acetyllactosamine units was substituted, and the type of substitution, differed. The substituents were alpha-NeuAc-(2----6), alpha-NeuAc-(2----3), and alpha-NeuAc-(2----3)[beta-GalNAc-(1----4)]. The carbohydrate moieties of the glycoprotein were heterogeneous also because of an uneven distribution of the fucose residues, which were attached to GlcNAc residues, both that linked to asparagine and one or more of those present in the N-acetyllactosamine units. The alpha-NeuAc-(2----3)[beta-GalNAc-(1----4)]-beta-Gal-(1---- sequence forms, at least in part, the Sda immunodeterminant. The pKa of the carboxyl group of the sialic acid residue in this entity is lower than that for molecules lacking Gal-NAc in this position. Thus, the difference in the number of Sda determinants carried by the glycopeptides enabled the latter to be fractionated on DEAE-Sephadex.

Infectivity and glycoprotein processing of herpes simplex virus type 1 grown in a ricin-resistant cell line deficient in N-acetylglucosaminyl transferase I

We report on the replication of herpes simplex virus type 1 (HSV-1) and viral glycoprotein processing in RicR14 cells, a mutant ricin-resistant cell line defective in N-acetylglucosaminyl transferase I activity. In these cells HSV-1(MP) and (F) replicated to yields very similar to those in parental BHK cells. The kinetics of HSV-1 adsorption in mutant and in parent cells was also essentially identical. Progeny virions from ricin-resistant and wild-type cells displayed comparable specific infectivities. However, in the mutant cells the efficiency of plating of progeny virus from both RicR14 and BHK cells was reduced. HSV-1(MP) failed to induce syncytia in RicR14 cells either in a plaque assay or after a high-multiplicity infection. Moreover, the fully glycosylated forms of glycoproteins (gB, gC, and gD) were totally absent, and only the partially glycosylated precursors (pgC, pgD. and a triplet in the gB-gA region) accumulated in HSV-1-infected ricin-resistant cells and in herpesvirions made in these cells. Consistent with these results analysis of pronase glycopeptides from cells labeled with [14C]glucosamine showed a strong decrease of sialylated complex-type oligosaccharides and a dramatic accumulation of the neutral mannose-rich chains. The latter chains predominate in partially glycosylated precursors, whereas the complex acidic chains predominate in the fully processed forms of HSV glycoproteins. These results taken together indicate that (i) host-cell N-acetylglucosaminyl transferase I participates in the processing of HSV glycoproteins; and (ii) infectivity of herpesvirions does not necessarily require the mature form of gB. The absence of HSV-1(MP)-induced fusion in RicR14 cells is discussed.

Studies on benzhydrazone, a specific inhibitor of herpesvirus glycoprotein synthesis. Size distribution of glycopeptides and endo-beta-N-acetylglucosaminidase-H treatment

Benzhydrazone is a bis-amidinohydrazone derivative which specifically hinders the formation of herpes simplex virus (HSV) glycoproteins. In this study we present some structural features of the oligosaccharide chains of herpesvirus glycoproteins synthesized in cells incubated with the inhibitor. Gel filtration analysis of glycopeptides, obtained through exhaustive pronase-digestion of infected cells after a long or a short labeling with 14C-glucosamine, showed that benzhydrazone reduced the appearance of glycopeptides of all the size-classes, including the mannose-rich glycopeptide with an approximate molecular weight of 1500. The same percent of label was released from both untreated and benzhydrazone-treated cells after digestion with endo-beta-N-acetylglucosaminidase H, an enzyme which cleaves between the N-acetylglucosamine residues in large high-mannose type oligosaccharides. This indicates that the relative amount of glycoproteins sensitive to this enzyme did not differ in the two kinds of samples. PAGE analysis confirmed that the same glycoproteins were digested in both samples. They were gA, pgC, and pgD, which therefore contain high-mannose type oligosaccharides. It is concluded that benzhydrazone hinders carbohydrate addition to herpesvirus proteins at an early step.