Inhibition of glycoprotein biosynthesis of influenza virus by D-glucosamine and 2-deoxy-D-glucose

Glycolytic interference blocks influenza A virus propagation by impairing viral polymerase-driven synthesis of genomic vRNA

Influenza A virus (IAV), like any other virus, provokes considerable modifications of its host cell's metabolism. This includes a substantial increase in the uptake as well as the metabolization of glucose. Although it is known for quite some time that suppression of glucose metabolism restricts virus replication, the exact molecular impact on the viral life cycle remained enigmatic so far. Using 2-deoxy-d-glucose (2-DG) we examined how well inhibition of glycolysis is tolerated by host cells and which step of the IAV life cycle is affected. We observed that effects induced by 2-DG are reversible and that cells can cope with relatively high concentrations of the inhibitor by compensating the loss of glycolytic activity by upregulating other metabolic pathways. Moreover, mass spectrometry data provided information on various metabolic modifications induced by either the virus or agents interfering with glycolysis. In the presence of 2-DG viral titers were significantly reduced in a dose-dependent manner. The supplementation of direct or indirect glycolysis metabolites led to a partial or almost complete reversion of the inhibitory effect of 2-DG on viral growth and demonstrated that indeed the inhibition of glycolysis and not of N-linked glycosylation was responsible for the observed phenotype. Importantly, we could show via conventional and strand-specific qPCR that the treatment with 2-DG led to a prolonged phase of viral mRNA synthesis while the accumulation of genomic vRNA was strongly reduced. At the same time, minigenome assays showed no signs of a general reduction of replicative capacity of the viral polymerase. Therefore, our data suggest that the significant reduction in IAV replication by glycolytic interference occurs mainly due to an impairment of the dynamic regulation of the viral polymerase which conveys the transition of the enzyme's function from transcription to replication.

Glucosamine to gold nanoparticles binding studied using Raman spectroscopy

The binding of glucosamine to gold in water solutions of glucosamine hydrochloride mixed with clean colloidal gold nanoparticles obtained by laser ablation in liquid was studied using surface-enhanced Raman scattering (SERS), dynamic light scattering (DLS) and UV-VIS spectroscopy. The purpose of this study was to establish whether the binding of charged aminogroup to gold nanoparticles (AuNPs) is taking place, and if it does, how can it be identified by means of SERS. The average size of dried gold nanoparticles was (20 ± 4) nm determined by averaging the sizes observed in transmission electron microscopy micrographs, which is smaller than the average size of gold nanoparticles in water solution as determined by DLS: (52 ± 2) nm. Upon adding the glucosamine solutions to gold colloid, average hydrodynamic diameter of ions was slightly larger for 0.1 mM glucosamine solution (55 ± 2 nm), while it increased to (105 ± 22) nm in the case of 1 mM solution, and was (398 ± 54) nm when 10 mM glucosamine solution was added. Most prominent Raman bands observed both for 0.1 mM and 1 mM glucosamine solutions were located at 1165 cm^-1, 1532 and 1586 cm^-1 and assigned to C-N coupled with C-C stretching, and C-NH₃⁺ deformation angles bending. In SERS spectrum of 1 mM GlcN⁺ solution, two strong bands at 999 and 1075 cm^-1 were found and attributed to C-O_ring stretching coupled with C-NH₃⁺ bending (999 cm^-1) and to dominantly C-O stretching vibration. The differences in SERS spectra are attributed to different number of glucosamine molecules that attach to gold nanoparticles and their orientation with respect to the metal particle surface, partly due to presence of beta anomers protonated at anomeric oxygen position. The assignment of glucosamine bands was further corroborated by comparison with vibrational spectra of alpha and beta glucose and of polycrystalline powder of glucosamine hydrochloride. For all three substances comprehensive calculation of vibrational density of states was conducted using density functional theory. Benchmark bands for polycrystalline glucose anomers distinction are 846 and 915 cm^-1 for alpha glucose, and 902 cm^-1 for beta glucose. However, the bands observed in SERS spectra of 0.1 mM glucosamine solution at 831, 899, and 946 cm^-1 or in 1 mM solution at 934 cm^-1 cannot be easily identified as belonging either to alpha or beta glucosamine anomer, due to complexity of atomic motions involved. The identification of vibrational bands associated with -CNH₃⁺ group will aid SERS studies on amino acids, especially in cases when several atomic groups could possibly bind to AuNPs.

The Modulatory Roles of N-glycans in T-Cell-Mediated Autoimmune Diseases

Glycosylation is a ubiquitous posttranslational modification of proteins that occurs in the endoplasmic reticulum/Golgi. N-glycans and mucin-type O-glycans are achieved via a series of glycohydrolase- and glycosyltransferase-mediated reactions. Glycosylation modulates immune responses by regulating thymocyte development and T helper cell differentiation. Autoimmune diseases result from an abnormal immune response by self-antigens and subsequently lead to the destruction of the target tissues. The modification of N-glycans has been studied in several animal models of T-cell-mediated autoimmune diseases. This review summarizes and highlights the modulatory effects of N-glycosylation in several autoimmune diseases, including multiple sclerosis, systemic lupus erythematosus, inflammatory bowel disease, and type 1 diabetes mellitus.

Glucosamine Modulates T Cell Differentiation through Down-regulating N-Linked Glycosylation of CD25

Glucosamine has immunomodulatory effects on autoimmune diseases. However, the mechanism(s) through which glucosamine modulates different T cell subsets and diseases remain unclear. We demonstrate that glucosamine impedes Th1, Th2, and iTreg but promotes Th17 differentiation through down-regulating N-linked glycosylation of CD25 and subsequently inhibiting its downstream Stat5 signaling in a dose-dependent manner. The effect of glucosamine on T helper cell differentiation was similar to that induced by anti-IL-2 treatment, further supporting an IL-2 signaling-dependent modulation. Interestingly, excess glucose rescued this glucosamine-mediated regulation, suggesting a functional competition between glucose and glucosamine. High-dose glucosamine significantly decreased Glut1 N-glycosylation in Th1-polarized cells. This finding suggests that both down-regulated IL-2 signaling and Glut1-dependent glycolytic metabolism contribute to the inhibition of Th1 differentiation by glucosamine. Finally, glucosamine treatment inhibited Th1 cells in vivo, prolonged the survival of islet grafts in diabetic recipients, and exacerbated the severity of EAE. Taken together, our results indicate that glucosamine interferes with N-glycosylation of CD25, and thereby attenuates IL-2 downstream signaling. These effects suggest that glucosamine may be an important modulator of T cell differentiation and immune homeostasis.

Triggering unfolded protein response by 2-Deoxy-D-glucose inhibits porcine epidemic diarrhea virus propagation

The unfolded protein response (UPR) is cyto-protective machinery elicited towards an influx of large amount of protein synthesis in the endoplasmic reticulum (ER). Extensive studies suggest that the UPR can also be activated during virus infection. In the present studies, we first evaluated if porcine epidemic diarrhea virus (PEDV) infection activated the UPR pathways. Electron microscopy analysis demonstrated the morphology changes of ER post-PEDV infection. Western blot and real-time PCR identified the differences of UPR genes in response to PEDV infection. The results suggested that PEDV infection induced UPR in Vero cells. Meanwhile, we silenced the expression of PKR-like ER kinase (PERK) by shRNA, we found that the knockdown of PERK increased virus loads in the cells, which was consistent with the result on 4-phenylbutyrate (4-PBA) treatment. We next determined whether 2-Deoxy-d-glucose (2-DG), an ER stress inducer, possessed antiviral activity against PEDV infection. Plaque formation assay, RT-PCR and Western blot analysis suggested that 2-DG might inhibit virus infection by affecting viral protein translation during the early stage of virus infection. Interestingly, we also found that 2-DG treatment could affect virus assembly, which is similar to previous studies on influenza virus. All these results support the therapeutic potential of using 2-DG or glucose/mannose analogs to induce the UPR to block virus replication.

Membrane Glycoproteins of Enveloped Viruses

This chapter focuses on the recent information of the glycoprotein components of enveloped viruses and points out specific findings on viral envelopes. Although enveloped viruses of different major groups vary in size and shape, as well as in the molecular weight of their structural polypeptides, there are general similarities in the types of polypeptide components present in virions. The types of structural components found in viral membranes are summarized briefly in the chapter. All the enveloped viruses studied to date possess one or more glycoprotein species and lipid as a major structural component. The presence of carbohydrate covalently linked to proteins is demonstrated by the incorporation of a radioactive precursor, such as glucosamine or fucose, into viral polypeptides, which is resolved by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Enveloped viruses share many common features in the organization of their structural components, as indicated by several approaches, including electron microscopy, surface-labeling, and proteolytic digestion experiments, and the isolation of subviral components. The chapter summarizes the detailed structure of the glycoproteins of four virus groups: (1) influenza virus glycoproteins, (2) rhabdovirus G protein, (3) togavirus glycoprotein, and (4) paramyxovirus glycoproteins The information obtained includes the size and shape of viral glycoproteins, the number of polypeptide chains in the complete glycoprotein structure, and compositional data on the polypeptide and oligosaccharide portions of the molecules.

Approaches and strategies for the treatment of influenza virus infections

Influenza A and B viruses belong to the Orthomyxoviridae family of viruses. These viruses are responsible for severe morbidity and significant excess mortality each year. Infection with influenza viruses usually leads to respiratory involvement and can result in pneumonia and secondary bacterial infections. Vaccine approaches to the prophylaxis of influenza virus infections have been problematic owing to the ability of these viruses to undergo antigenic shift by exchanging genomic segments or by undergoing antigenic drift, consisting of point mutations in the haemagglutinin (HA) and neuraminidase (NA) genes as a result of an error-prone viral polymerase. Historically, antiviral approaches for the therapy of both influenza A and B viruses have been largely unsuccessful until the elucidation of the X-ray crystallographic structure of the viral NA, which has permitted structure-based drug design of inhibitors of this enzyme. In addition, recent advances in the elucidation of the structure and complex function of influenza HA have resulted in the discovery of a number of diverse compounds that target this viral protein. This review article will focus largely on newer antiviral agents including those that inhibit the influenza virus NA and HA. Other novel approaches that have entered clinical trials or been considered for their clinical utility will be mentioned.

The significance of carbohydrate trimming for the antigenicity of the Semliki Forest virus glycoprotein E2

Six groups, designated a-f, of noncompeting murine monoclonal antibodies to the envelope glycoprotein E2 of Semliki Forest virus (SFV) have been used to analyze antigenic changes caused by differences in the carbohydrate chain composition of the envelope glycoprotein E2 in the virion. Deletion of terminal sialic acids as observed in virus progeny from mosquito cells did not affect antigenic properties. Inhibition of the trimming pathway in infected chicken cells by the mannosidase I inhibitor dMM led to infectious virus particles containing mannose-rich oligosaccharides of the composition Man9(GlcNAc)2 in the envelope glycoproteins. This alteration had no effect on antigenicity. If inhibition was, however, performed with MdN which acts on alpha-glucosidase giving rise to virions with glycoproteins containing three additional glucose residues in the carbohydrate chains [Glc3Man7,8,9(GlcNAc)2], significant antigenic changes were observed. The six epitopes were differently affected by the underlying structural change and the pattern of exposition of epitopes was not identical with that observed after cleavage of intramolecular disulfide bonds. Concomitantly, the cleavage rate of gp62, the intracellular precursor molecule of the glycoproteins E2 and E3 of the virus particle, was reduced causing a reduction of virus yield. It is concluded that the existence of untrimmed carbohydrate chains is sufficient to allow SFV maturation. The trimming reactions improve this process in a matter suggesting that the carbohydrate chains influence intracellular traffic (addressing) of the respective glycoprotein.

Structural diversity of the major surface antigen of Plasmodium falciparum merozoites

The structures of the major merozoite surface antigen of Plasmodium falciparum and the gene encoding it were indistinguishable for the Wellcome strain and the Thai clone T9/94 but different for clones T9/96, T9/98, and T9/101. The central portion of the gene is subject to the greatest variation in structure. The protein from all five lines was found to be posttranslationally modified by covalent addition of both carbohydrate and fatty acid.

Structural diversity of the major surface antigen of Plasmodium falciparum merozoites

The structures of the major merozoite surface antigen of Plasmodium falciparum and the gene encoding it were indistinguishable for the Wellcome strain and the Thai clone T9/94 but different for clones T9/96, T9/98, and T9/101. The central portion of the gene is subject to the greatest variation in structure. The protein from all five lines was found to be posttranslationally modified by covalent addition of both carbohydrate and fatty acid.

Analysis of tyrosinases as asparagin-linked oligosaccharides by concanavalin A lectin chromatography: appearance of new segment of tyrosinases in melanoma cells following interrupted melanogenesis induced by glycosylation inhibitors

The structural alteration of carbohydrate moieties of tyrosinases associated with the depigmentation process induced by glycosylation inhibition has been investigated by using concanavalin A (Con A) affinity chromatography. Con A affinity chromatography of deoxycholate-solubilized large and small granule fractions shows that while all tyrosinases found in control B-16 cells exhibit affinity to Con A lectin, there is an emergence on non-Con A binding tyrosinases in the unpigmented cells induced by glycosylation inhibitors, such as tunicamycin and glucosamine. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, control tyrosinase activity forms 2 distinct bands consisting of T1 and T3. But tyrosinases from the unpigmented cells lose T3 tyrosinase and are resolved into a few different molecular weight components, one of which is Con A affinitive T1 tyrosinase and the others are non-Con A affinitive tyrosinases with smaller molecular weights than the T1 tyrosinase. These findings suggest that altered structures of carbohydrate moiety in tyrosinase molecules play a role in the induction of loss of membrane-binding capacity of tyrosinases, resulting in the loss of melanization in pigment cells.

Identification of a glycosidase activity with apparent specificity for 2-deoxy-D-glucose in glycosidic linkage

2-Deoxy-D-glucose (dGlc) is a carbohydrate with significant activity as an inhibitor of glucose metabolism and as a precursor in the synthesis of glycosylated macromolecules; several of the enzymes associated with its metabolism remain uncharacterized. In the present report, the partial purification and some of the properties of a mammalian enzyme that appears to be relatively specific for the hydrolysis of dGlc bound in glycosidic linkage is described. The physiological function of this enzymatic activity is unknown. In addition, dGlc has been shown to be taken up by HTC cells in culture and incorporated into macromolecular bound form, both as dGlc and as 2-deoxygalactose which is formed from dGlc.

Glucose requirement for induction by sodium butyrate of the glycoprotein hormone alpha subunit in HeLa cells

Butyric acid produces multiple effects on mammalian cells in culture, including alterations in morphology, depression of growth rate, increased histone acetylation, and modified production of various proteins and enzymes. The latter effect is exemplified by the induction in HeLa cells of the glycoprotein hormone alpha subunit by millimolar concentrations of the fatty acid. This report demonstrates that increased subunit accumulation in response to sodium butyrate is strikingly dependent on the presence of glucose (or mannose) in the growth medium. In contrast, basal levels of subunit synthesis are only marginally affected when the culture medium is supplemented with one of a variety of hexoses. An increase in the accumulation of HeLa alpha does not occur in medium containing pyruvate as the energy source, and sustained induction requires the simultaneous and continued presence of both glucose and butyrate. The effects of butyrate on HeLa cell morphology and subunit induction can be separated, since the latter is glucose-dependent while the former is not. Failure of butyrate to induce alpha in medium containing pyruvate does not result from restricted subunit secretion, since the levels of intracellular alpha are not increased disproportionately relative to those in the medium. The hexoses which support induction of HeLa alpha (glucose greater than or equal to mannose greater than galactose greater than fructose) are identical to those which have been shown previously to stimulate the glucosylation of lipid-linked oligosaccharides and enhance the synthesis of certain glycoproteins. Labeling of various glycosylation intermediates with [3H]mannose indicates that in glucose medium there is a decrease in the level of radioactivity associated with both dolicholpyrophosphoryl oligosaccharide and cellular glycoproteins and a concomitant increase in the fraction of label recovered in secreted glycoproteins. Butyrate also causes a decrease in [3H]mannose-labeled cellular glycoproteins and an increase in tritiated extracellular glycoproteins, particularly in glucose medium. Likewise, glucose stimulates the incorporation of [3H]glucosamine into immunoprecipitable alpha subunit relative to the bulk of HeLa-secreted glycoproteins, and this is further enhanced by butyrate. However, as demonstrated by lectin chromatography of conditioned media, a nonglycosylated subunit does not accumulate in pyruvate medium, either in the absence or presence of butyrate.(ABSTRACT TRUNCATED AT 400 WORDS)

A simple procedure for the analysis of the structural proteins of influenza and parainfluenza viruses involving adsorption to erythrocytes

A simple procedure for the analysis of the structural proteins of influenza and parainfluenza viruses utilizing adsorption to erythrocytes is described. The method involves virus growth in the presence of [35S]methionine, adsorption of clarified culture medium with a 0.5% suspension of either guinea-pig or chicken erythrocytes and analysis of the virus-erythrocyte aggregates by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). All of the structural proteins can be detected using this procedure, and the protein profiles of virus-adsorbed erythrocyte complexes compare extremely well with those of sucrose density gradient purified virus preparations.

Poliovirus and vesicular stomatitis virus replication in the presence of 6-diazo-5-oxo-L-norleucine or 2-deoxy-D-glucose

The effects of 6-diazo-5-oxo-L-norleucine (DON), 2-deoxy-D-glucose (DOG), and tunicamycin (TM) on the replication of poliovirus (PV) and vesicular stomatitis virus (VSV) were examined. During a 48-hr replication period, TM, DON, and DOG inhibit VSV plaque formation in HEp-2 cells by 99.9%, 99.8%, and 99.9% respectively. Inhibition of VSV by DON is reversed with glutamine. Although all three agents are known to affect glycoprotein synthesis, DON and DOG also inhibit plaque formation of viruses devoid of structural glycoproteins. Thus, plaque formation of PV types 1 and 3 and Coxsackie B3 virus is delayed in HEp-2 and Buffalo green monkey kidney cells during exposure to these agents. Since these viruses do not contain glycoproteins and since concentrations up to 10 micrograms TM/ml cause no significant inhibition of PV, DON and DOG are affecting another viral or cellular process. Inhibition of PV replication by DON is reversed by addition of 25 mM glutamine or marginally by exposure to a combination of 5 mM concentrations of cytidine, uridine, adenosine monophosphate, and guanosine monophosphate. Inhibition of PV replication by DOG is reversed with 5 mM uridine alone. During DON exposure of HEp-2 cells infected with PV, the amount of 3H-uridine incorporation at 5.5 hr postinfection (pi) is reduced to 53% of untreated controls, an amount 11% greater than incorporation in cultures infected with PV but not treated with DON. These data indicate that the inhibition of PV replication by DON or DOG occurs at the level of viral RNA synthesis, while the primary target of these agents during VSV replication is probably glycosylation.

Isolation and characterization of a variant of mouse plasmacytoma J558 synthesizing a 110,000-dalton immunoglobulin heavy chain and of secondary variants synthesizing either a 55,000-dalton or an 80,000-dalton immunoglobulin heavy chain: possible implications

A mutant has been isolated from the J558 (immunoglobulin A, lambda, anti-alpha 1 leads to 3 dextran) cell line which synthesizes a heavy-chain immunoglobulin twice the size of normal heavy chain. Secondary variants that synthesized heavy chains either 1.5 times as large as wild type or the same size as wild type were identified. All mutants were serologically immunoglobulin continued to bind antigen, and retained the individual idiotype of the parent. Northern blot analysis and in vitro synthesis studies showed that the large heavy chains were primary synthetic products and not the consequence of abnormal covalent bonds. Cleavage of genomic DNA with restriction endonucleases and molecular hybridization studies showed new fragments in the 2 X and 1.5 X mutants which disappeared in the 1 X revertant. These data cannot easily be reconciled with the mutants arising either by unequal recombination or gene conversion. Further molecular characterization of these mutants should give additional insight into immunoglobulin gene evolution.

Isolation and characterization of a variant of mouse plasmacytoma J558 synthesizing a 110,000-dalton immunoglobulin heavy chain and of secondary variants synthesizing either a 55,000-dalton or an 80,000-dalton immunoglobulin heavy chain: possible implications

A mutant has been isolated from the J558 (immunoglobulin A, lambda, anti-alpha 1 leads to 3 dextran) cell line which synthesizes a heavy-chain immunoglobulin twice the size of normal heavy chain. Secondary variants that synthesized heavy chains either 1.5 times as large as wild type or the same size as wild type were identified. All mutants were serologically immunoglobulin continued to bind antigen, and retained the individual idiotype of the parent. Northern blot analysis and in vitro synthesis studies showed that the large heavy chains were primary synthetic products and not the consequence of abnormal covalent bonds. Cleavage of genomic DNA with restriction endonucleases and molecular hybridization studies showed new fragments in the 2 X and 1.5 X mutants which disappeared in the 1 X revertant. These data cannot easily be reconciled with the mutants arising either by unequal recombination or gene conversion. Further molecular characterization of these mutants should give additional insight into immunoglobulin gene evolution.

The role of carbohydrate in determining the immunochemical properties of the hemagglutinin of influenza A virus

Most of the carbohydrate was removed from influenza virus MRC II (H3N2) and its purified hemagglutinin (HA) on treatment with glycosidases, including alpha-mannosidase, beta-N-acetylglucosaminidase, beta-galactosidase and alpha-fucosidase. The release of 50 per cent of the carbohydrate from intact virus particles significantly affected hemagglutinating activity. The ability of untreated and glycosidase-treated virus to inhibit the binding of antibodies directed against the hemagglutinin was almost indistinguishable by competitive radioimmunoassay (RIA). Up to 60 per cent of the carbohydrate from the purified HA of influenza virus could be removed. The antigenicity of glycosidase treated HA molecules decreased 8-fold compared to intact HAs as measured by competitive RIA. In addition, glycosidase digestion of 125I-labeled HA resulted in a decrease in its reactivity in direct RIA. We conclude that the carbohydrate portion of the HA of influenza virus is not of major importance in defining the antigenicity of HA.

Selective inhibition of herpes simplex virus glycoprotein synthesis by a benz-amidinohydrazone derivative

1H-benz[f]indene-1.3(2H)dione-bis-amidinohydrazone (benzhydrazone) inhibited incorporation of 14C-glucosamine, 14C-fucose and 14C-mannose into glycoproteins of HEp-2 cells infected with various strains of herpes simplex virus 1 (HSV-1) and impaired RNA and protein synthesis to a low extent. These biochemical effects are very similar to those induced by glycosylation inhibitors such as tunicamycin, D-glucosamine and 2-deoxy-D-glucose. In contrast to these inhibitors, benzhydrazone reduced HSV glycoprotein synthesis selectively since it did not significantly modify i) the saccharide uptake into glycoproteins of uninfected and of Sindbis virus-infected cells, ii) viral growth and cell fusion in paramyxovirus-infected cells, two activities which depend on viral glycoprotein synthesis. Benzhydrazone had only minor effects on the overall metabolism of uninfected cells, since it did not alter cell growth rate, and amino acid, uridine, and hexose incorporations were about 80% those of untreated cells.

Processing of influenza HA protein in MDCK cells: components with different mobilities in polyacrylamide gel electrophoresis and their precursor-product relationships

In influenza virus-infected MDCK cells labelled with 14C-chlorella hydrolysate or 35S-methionine a virus-specific protein component is revealed migrating slightly faster than HA protein in polyacrylamide gel electrophoresis. Under chase conditions the component disappears either completely or partially, with a concomitant intensification of the HA band. The rate and extent of this transition are strain-dependent. Both the HA band and the faster moving component are not revealed if the cells are labelled in the presence of 20 mM of D-glucosamine. In primary cell cultures of chick embryos a single HA band with a mobility similar to that of the faster moving component in MDCK cells has been observed. It is suggested that the transition of the label from the faster moving component to the HA band reflects the final step of HA processing specific for MDCK cells.

Structure of bromelain-released influenza virus haemagglutinin as revealed by electrophoresis, sedimentation and electron microscopy

Sigma bromelain (EC 3.4.22.4) was used to isolate the haemagglutinin (HA) from the MRC-11 (H3N2) and A/U.S.S.R./90/77 (H1N1) influenza A virus strains. Sedimentation analysis of bromelain-solubilized preparations revealed 9.5S and 5.5S protein components, the former being identified as the bromelain-released haemagglutinin (BHA). No residual neuraminidase (NA) activity was detected in the BHA isolated from the MRC-11 strain whereas up to 80 per cent of the enzymatically active NA was found to be preserved in the electrophoretically pure BHA isolated from the A/U.S.S.R./90/77 strain. Increased electrophoretic mobilities were exhibited by both the light and heavy chains of the BHA subunit. The difference observed in the molecular weights of the polypeptide fragments removed by bromelain from the light chains is interpreted in terms of the different depth of penetration of antigenically distinct HAs through the influenza virus lipid membrane. Splitting off of approximately 15 and 26 per cent of the sugars from the carbohydrate portions of the light and heavy chains respectively, was demonstrated. This suggested involvement of glycosidase impurities present in the bromelain preparation employed. The rod-shaped BHA molecules proved to be 110 +/- 5 Angstrom long and 40 +/- 5 Angstrom wide as measured by electron microscopy. It is proposed that the 45,000-molecular-weight polypeptide observed constantly in egg-grown influenza viruses is host actin.

Inhibition of T cell-mediated cytolysis by 2-deoxy-D-glucose:dissociation of the inhibitory effect from glycoprotein synthesis

Previous studies have established that T cell-mediated cytolysis can be reversibly inhibited by the hexose analogue 2-deoxy-D-glucose (2-DG) by a mechanism which is apparently unrelated to energy depletion. The possibility that the inhibitory effect of 2-DG on cytolysis was linked to its known inhibitory effect on glycoprotein synthesis was therefore investigated. In contrast to the results obtained with 2-DG, no inhibition of cytolysis was observed in the presence of tunicamycin, a potent and specific inhibitor of lipid carrier-dependent protein glycosylation. Furthermore, populations of cytolytic cells which had been pretreated with doses of tunicamycin sufficient to block the incorporation of mannose (or 2-DG) into glycoproteins were still fully susceptible to inhibition by 2-DG. Other known inhibitors of viral protein glycosylation, such as glucosamine and galactosamine, inhibited cytolysis only weakly under conditions where 2-DG was highly effective. Kinetic studies revealed that the inhibitory effect of 2-DG on cytolysis could be reversed within minutes by the addition of exogenous glucose. Furthermore, suggestive evidence was obtained that inhibition cytolysis by 2-DG was linked to a parallel inhibition of effector: target cell binding. Taken together, these results strongly suggest that the inhibitory effect of 2-DG on cytolysis can be dissociated from its effect on protein glycosylation. An alternative mechanism of action of 2-DG is suggested.

Formation of 2-deoxyglucose-containing lipid-linked oligosaccharides. Interference with glycosylation of glycoproteins

Crude membrane preparations from chick embryo cells catalyse the formation of dolichyl-di-N-acetylchitobiosyl diphosphate [Dol-PP-(GlcNAc)2] from uridine diphosphate N-acetylglucosamine (UDP-GlcNAc). The formation of this glycolipid was stimulated by exogenous dolichyl phosphate and inhibited by tunicamycin. Adding GDP-mannose to the cell-free system containing Dol-PP-(GlcNAc)2 by preincubation led to the formation of a lipid-linked oligosaccharide, containing 8--9 sugar residues. The formation of lipid-linked oligosaccharides was inhibited by GDP-2-deoxy-D-glucose (GDP-dGlc): in this case Dol-PP-(Glc-NAc)2-dGlc accumulated. Subsequent additions of mannosyl residues to this trisaccharide-lipid to form lipid-linked oligosaccharides were not possible. Concomitantly the glycosylation of proteins was blocked. Partially inhibitory conditions were obtained by adding both GDP-dGlc and GDP-Man with an excess of GDP-dGlc. Glycosylation of proteins was observed but the glycopeptides did not contain 2-deoxyglucosyl residues. Also in these cases 2-deoxyglucose-containing glycolipids accumulated. The main glycolipid formed under these conditions was Dol-PP-(GlcNAc)2-Man-dGlc. Lipid-linked oligosaccharides containing 2-deoxyglucose were formed under these conditions, although in small amounts, but were not transferred to protein. So the molecular basis of the inhibitory action of 2-deoxyglucose on glycosylation of protein is the incorporation of 2-deoxyglucosyl residues during early phases of the biosynthesis of the lipid-linked oligosaccharides.

Removal of carbohydrate from influenza A virus and its hemagglutinin and the effect on biological activities

Treatment of influenza virus and its purified hemagglutining with glycosidases from Diplococcus pneumoniae, which included beta-galactosidase, beta-N-acetylglucosminidase, and endoglycosidase D, released amino and neutral sugars from the virus and these as well as large oligosaccharides from the purified hemagglutinin. The released glucosamine-containing oligosaccharides were of one discrete size. Large oligosaccharides not removed by the glycosidases were found on the virus as well as the hemagglutinin. Some oligosaccharides on the virus were inaccessible to the enzymes, since they could be removed only from the purified hemagglutinin. Approximately 50% of the hemagglutinin carbohydrates could be removed without effect on hemagglutinating activity. Similarly, removal of 20 to 25% of the carbohydrates from intact virus particles did not alter infectivity.

Purification of the influenza hemagglutinin glycoprotein and characterization of its carbohydrate components

Hemagglutinin from influenza A/PR8 virus was purified after treatment of the virus with sodium deoxycholate followed by extraction with tri-n-butyl phosphate. This fully disrupted the virus while preserving hemagglutinating activity. The hemagglutinin was obtained in the form of small aggregates that could be separated from other viral components. Purified hemagglutinin was hydrolyzed to determine carbohydrate composition and digested with Pronase to analyze oligosaccharide structures. Sugars present in the hemagglutinin were galactose, mannose, fucose, and glucosamine in molar rates of about 6:11:2:5, and these comprised 16% of the hemagglutinin glycoprotein. Oligosaccharides obtained from virus included a major component of a molecular weight of 2,800, composed of glucosamine, galactose, mannose, and fucose, and a minor heterogenous component of a molecular weight of 1,500 to 2,000, containing predominantly mannose. The 2,800-molecular-weight oligosaccharide was a constituent of the hemagglutinin, and treatment of this large oligosaccharide with specific exo-glycosidases demonstrated the presence of terminal galactose and fucose and allowed the deduction of a general structure for this component.

Studies on antiviral glycosides. Synthesis and biological evaluation of various phenyl glycosides

A variety of analogues and derivatives of phenyl glycosides were synthesized for examination of their biological activities and of the relationship between structure and antiviral activity. For antiviral activity, a 6-deoxy-6-halogeno-D-glucose residue was most suitable for the carbohydrate moiety and p-alkylphenyl groups for the aglycone moiety. Based on these results, p-(sec-butyl)phenyl 6-chloro-6-deoxy-beta-D-glucopyranoside and p-(sec-butyl)phenyl 6-deoxy-6-iodo-beta-D-glucopyranoside were prepared, and the former compound was found to be the most potent antiviral substance, in this series, against influenza and Herpes simplex virus. The anomeric configuration of phenyl glycosides did not contribute to the antiviral activity.

Role of carbohydrates in protein secretion and turnover: effects of tunicamycin on the major cell surface glycoprotein of chick embryo fibroblasts

Using tunicamycin, we have investigated the role of glycosylation in the biosynthesis, processing and turnover of CSP, the major cell surface glycoprotein of chick embryo fibroblasts (CEF). This antibiotic specifically inhibits glycosylation mediated by dolichol pyrophosphate and consequently inhibits the glycosylation of asparaginyl residues of glycoproteins. Tunicamycin inhibited the incorporation of 3H-mannose into CSP by 92--98% and 14C-glucosamine by 84--96%, whereas total protein synthesis was decreased by only 15--45%. Tunicamycin treatment decreased total amounts of CSP by approximately 50--65%, with equal decreases in CSP occurring on the cell surface and in culture medium, whereas intracellular pools of CSP were not substantially affected. In contrast to CSP, three other membrane-associated proteins of apparent molecular weights 75,000, 95,000 and 150,000 daltons were found in increased amounts. Procollagen secretion was not inhibited by tunicamycin. Both procollagen and CSP secretion into culture medium were also not increased in AD6, a glycosylation-deficient, mutant mouse 3T3 cell line compared to wild-type cells. We examined the mechanism of the decrease in CSP after tunicamycin treatment. The rate of CSP biosynthesis as measured by pulse-labeling with 14C-leucine was not altered. Tunicamycin had only a slight effect on the initial times and rates of CSP appearance on the cell surface; some apparent intracellular redistribution of CSP was detected by immunofluorescence. The major effect of tunicamycin treatment was to accelerate the rate of degradation of CSP 2--3 fold. This increase is sufficient to account for the observed decreases after tunicamycin treatment. Our results suggest that carbohydrates may not be essential for CSP or procollagen synthesis, intracellular processing and secretion, but that carbohydrates may help stabilize CSP against proteolytic degradation.

Reversible changes in cytolytic T lymphocyte function induced by hyperthermia

The ability of cytolytic T lymphocytes (CTL) generated in vitro in mixed leucocyte cultures (MLC) to "repair" functional damage induced by moderate hyperthermia has been investigated. Repair of CTL function was assessed in a split dose system in which MLC cells were exposed to a total of 20 min at 43 degrees C delivered either as a single treatment or as two 10 min fractions separated by an interval at 37 degrees C. Significant repair was observed within 15 min at 37 degrees C in the split-dose protocol and maximum repair (corresponding to a 30-100-fold increase in lytic activity) was seen after 1.5-2 h. Repair was both temperature and energy dependent and was apparently related to a reversible lesion in the cytolytic mechanism itself. The effect of a number of metabolic inhibitors (and other agents) on repair was determined, but the precise nature of the heat-induced lesion could not be identified.