The Sialic Acids

Microscale Quantification of the Inhibition of Neuraminidase Using Capillary Nanogel Electrophoresis

Neuraminidase inhibitors modulate infections that involve sialic acids, making quantitative analyses of this inhibitory effect important for selecting and designing potential therapeutics. An automated nanogel capillary electrophoresis system is developed that integrates a 5 nL enzyme inhibition reaction in line with a 5 min separation-based assay of the enzymatic product to quantify inhibition as the half maximal inhibitory concentration (IC50) and inhibitor constant (Ki). A neuraminidase enzyme from Clostridium perfringens is non-covalently immobilized in a thermally tunable nanogel positioned in the thermally controlled region of the capillary by increasing the capillary temperature to 37 °C. Aqueous inhibitor solutions are loaded into the capillary during the nanogel patterning step to surround the enzyme zone. The capillary electrophoresis separation provides a means to distinguish the de-sialylated product, enabling the use of sialyllactose which contains the trisaccharide motif observed on serine/threonine-linked (O-linked) glycans. A universal nanogel patterning scheme is developed that does not require pre-mixing of enzymes with inhibitors when an automated capillary electrophoresis instrument is used, thus reducing the consumption of enzymes and enabling adaption of the method to different inhibitors. The universal approach is successfully applied to two classical neuraminidase inhibitors with different electrophoretic mobilities. The IC50 and Ki values obtained for N-acetyl-2,3-dehydro-2-deoxyneuraminic acid (DANA) are 13 ± 3 and 5.0 ± 0.9 μM, respectively, and 28 ± 3 and 11 ± 1 μM, respectively, for Siastatin B. These values agree with literature reports and reflect the weaker inhibition anticipated for Siastatin B in comparison to DANA.

Role of MUC1 in lubrication of pleural mesothelial cells cultured on fibrine gel

To elucidate the role of sialomucin in friction reduction, we investigated the sliding friction of pleural mesothelial cells monolayers cultured on fibrine gel. These measurements were performed on normal (4/4 RM-4) and on tumor (CARM-L1 TG3) cell lines. The effect of treatment with neuraminidase, which removes sialic acid from sialomucin, and of dexamethasone, which has shown to increase sialomucin expression, were also assessed. Furthermore, the expression of the main form of cell-surface-associated mucin (MUC1) present in the mesothelium, was assessed by western blot and immunofluorescence, under different experimental conditions. Expression of MUC1 was not significantly different in the two cell lines. Moreover, dexamethasone did not increase the expression of MUC1. Coefficient of kinetic friction (μ) was significantly higher in tumor cells than in normal cells. Neuraminidase increased μ in both cell lines. These results suggest that sialomucin may play a role in reducing the friction of pleural mesothelial cells.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Microscale Measurements of Michaelis-Menten Constants of Neuraminidase with Nanogel Capillary Electrophoresis for the Determination of the Sialic Acid Linkage

Phospholipid nanogels enhance the stability and performance of the exoglycosidase enzyme neuraminidase and are used to create a fixed zone of enzyme within a capillary. With nanogels, there is no need to covalently immobilize the enzyme, as it is physically constrained. This enables rapid quantification of Michaelis-Menten constants (K_M) for different substrates and ultimately provides a means to quantify the linkage (i.e., 2-3 versus 2-6) of sialic acids. The fixed zone of enzyme is inexpensive and easily positioned in the capillary to support electrophoresis mediated microanalysis using neuraminidase to analyze sialic acid linkages. To circumvent the limitations of diffusion during static incubation, the incubation period is reproducibly achieved by varying the number of forward and reverse passes the substrate makes through the stationary fixed zone using in-capillary electrophoretic mixing. A K_M value of 3.3 ± 0.8 mM (V_max, 2100 ± 200 μM/min) was obtained for 3'-sialyllactose labeled with 2-aminobenzoic acid using neuraminidase from Clostridium perfringens that cleaves sialic acid monomers with an α2-3,6,8,9 linkage, which is similar to values reported in the literature that required benchtop analyses. The enzyme cleaves the 2-3 linkage faster than the 2-6, and a K_M of 2 ± 1 mM (V_max, 400 ± 100 μM/min) was obtained for the 6'-sialyllactose substrate. An alternative neuraminidase selective for 2-3 sialic acid linkages generated a K_M value of 3 ± 2 mM (V_max, 900 ± 300 μM/min) for 3'-sialyllactose. With a knowledge of V_max, the method was applied to a mixture of 2-3 and 2-6 sialyllactose as well as 2-3 and 2-6 sialylated triantennary glycan. Nanogel electrophoresis is an inexpensive, rapid, and simple alternative to current technologies used to distinguish the composition of 3' and 6' sialic acid linkages.

Effect of alpha 2,6 sialylation on integrin-mediated adhesion of breast cancer cells to fibronectin and collagen IV

AIMS

To determine the role of sialylation on α5β1 and α2β1 integrins in the regulation of adhesion between breast cancer cells and extracellular matrix (ECM).

MAIN METHODS

Static cell adhesion assays were performed to quantify avidity of breast cancer cells to ECM. The effects of sialidases on α2,6 sialylation was assessed by flow cytometry using biotin conjugated Sambucus nigra lectin. Lectin affinity assays were used to determine expression of α2,6 sialylated integrins. Cell migration and invasion were investigated by wound healing and transwell invasion assays.

KEY FINDINGS

α2, α5 and β1 integrins had considerable α2,6 sialylation on MDA-MB-231 cells, whereas signals from MCF-7 cells were undetectable. Cleavage of α2,6 sialylation increased adhesion of MDA-MB-231 cells to ECM, while adhesion of MCF-7 cells was unaffected, consistent with the latter's lack of endogenous α2,6 sialylated surface integrins. Neither surface expression of α2β1 and α5β1 integrins, nor activated β1 integrin, changed in MDA-MB-231 cells after sialidase treatment. However, sialidase treatment did not have significant impact on migration or invasion of MDA-MB-231 cells.

SIGNIFICANCE

Cell adhesion is an important early step of cancer metastasis, yet the roles of sialylation in regulating integrin-mediated breast cancer cell adhesion in comparison to migration and invasion are not well-understood. Our data suggest desialylation of α2,6-sialylated integrins increases adhesion, but not migration or invasion, of MDA-MB-231 cells to ECM without altering integrin expression. It should be considered that α2,6 sialylation may play different roles in regulating cell adhesion of different cancer cells when developing potential therapeutics targeting α2,6 sialylation.

Effects of gangliosides on the activity of the plasma membrane Ca2+-ATPase

Control of intracellular calcium concentrations ([Ca(2+)]i) is essential for neuronal function, and the plasma membrane Ca(2+)-ATPase (PMCA) is crucial for the maintenance of low [Ca(2+)]i. We previously reported on loss of PMCA activity in brain synaptic membranes during aging. Gangliosides are known to modulate Ca(2+) homeostasis and signal transduction in neurons. In the present study, we observed age-related changes in the ganglioside composition of synaptic plasma membranes. This led us to hypothesize that alterations in ganglioside species might contribute to the age-associated loss of PMCA activity. To probe the relationship between changes in endogenous ganglioside content or composition and PMCA activity in membranes of cortical neurons, we induced depletion of gangliosides by treating neurons with d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (d-PDMP). This caused a marked decrease in the activity of PMCA, which suggested a direct correlation between ganglioside content and PMCA activity. Neurons treated with neuraminidase exhibited an increase in GM1 content, a loss in poly-sialoganglioside content, and a decrease in PMCA activity that was greater than that produced by d-PDMP treatment. Thus, it appeared that poly-sialogangliosides had a stimulatory effect whereas mono-sialogangliosides had the opposite effect. Our observations add support to previous reports of PMCA regulation by gangliosides by demonstrating that manipulations of endogenous ganglioside content and species affect the activity of PMCA in neuronal membranes. Furthermore, our studies suggest that age-associated loss in PMCA activity may result in part from changes in the lipid environment of this Ca(2+) transporter.

Axonal fasciculation and the role of polysialic acid-neural cell adhesion molecule in rat cortical neurons

Axonal fasciculation is a mechanism deployed by growing axons to reach their targets during development of the nervous system. Published data have suggested the involvement of neuronal cell adhesion molecules (NCAM) in axonal fasciculation. We have characterized the formation of axonal fascicles in serum-free, primary cultures of cortical neurons from embryonic rat brains. Unlike the published data, axonal fascicles in our system have a unique morphology: they are waveform, are rarely thicker than 20 μm, and can reach up to several millimeters in length. We observed an age and time dependence in the formation of fascicles. They formed only in cultures from embryonic day 15-17 brain and only between 4 days in vitro (DIV) and 11 DIV. Electron microscopy showed that the fascicles consisted of mostly axonal processes. Immunocytochemical staining confirmed that the fascicles were positive for the 66-kDa neurofilament protein, NF66, but they contained few, if any, microtubule-associated protein-2-positive or glial fibrillary acidic protein-positive processes. Polysialic acids appeared to be critical in the formation of fascicles. Neuraminidase treatment prevented the formation of fascicles when added before 5 DIV. Addition of a specific inhibitor blocked the effect of neuraminidase. The cortical neurons in our model shared several important features with axon fasciculation in vivo and may provide a unique system for studying the molecular mechanisms involved in the formation of axonal tracts in the brain.

A surface-exposed neuraminidase affects complement resistance and virulence of the oral spirochaete Treponema denticola

Neuraminidases (sialidases) catalyse the removal of terminal sialic acid from glycoconjugates. Bacterial pathogens often utilize neuraminidases to scavenge host sialic acid, which can be utilized either as a nutrient or as a decorating molecule to disguise themselves from host immune attacks. Herein, a putative neuraminidase (TDE0471) was identified in Treponema denticola, an oral spirochaete associated with human periodontitis. TDE0471 is a cell surface-exposed exo-neuraminidase that removes sialic acid from human serum proteins; it is required for T.denticola to grow in a medium that mimics gingival crevice fluid, suggesting that the spirochaete may use sialic acid as a nutrient in vivo. TDE0471 protects T.denticola from serum killing by preventing the deposition of membrane attack complexes on the bacterial cell surface. Animal studies revealed that a TDE0471-deficient mutant is less virulent than its parental wild-type strain in BALB/C mice. However, it causes a level of tissue damage similar to the wild type in complement-deficient B6.129S4-C3(tm1) (Crr) /J mice albeit the damage caused by both bacterial strains is more severe in these transgenic mice. Based on these results, we propose that T.denticola has evolved a strategy to scavenge host sialic acid using its neuraminidase, which allows the spirochaete to acquire nutrients and evade complement killing.

An eight-segment swine influenza virus harboring H1 and H3 hemagglutinins is attenuated and protective against H1N1 and H3N2 subtypes in pigs

Swine influenza virus (SIV) infections continue to cause production losses in the agricultural industry in addition to being a human public health concern. The primary method of controlling SIV is through vaccination. The killed SIV vaccines currently in use must be closely matched to the challenge virus, and their protective efficacy is limited. Live attenuated influenza vaccines (LAIV) provide strong, long-lived cell-mediated and humoral immunity against different influenza virus subtypes with no need for antigen matching. Here we report the generation of a new potential LAIV, an eight-segment SIV harboring two different SIV hemagglutinins (HAs), H1 and H3, in the genetic background of H1N1 SIV. This mutant SIV was generated by fusing the H3 HA ectodomain from A/Swine/Texas/4199-2/98 (H3N2) to the cytoplasmic tail, transmembrane domain, and stalk region of neuraminidase (NA) from A/Swine/Saskatchewan/18789/02 (H1N1) SIV. While this H1-H3 chimeric SIV, when propagated in vitro in the presence of exogenous neuraminidase, showed kinetics and growth properties similar to those of the parental wild-type virus, in vivo it was highly attenuated in pigs, demonstrating a great potential for serving as a dual LAIV. Furthermore, vaccination with the H1-H3 virus elicited robust immune responses, which conferred complete protection against infections with both H1 and H3 SIV subtypes in pigs.

Catalytic preference of Salmonella typhimurium LT2 sialidase for N-acetylneuraminic acid residues over N-glycolylneuraminic acid residues

In a comparison of sialidase activities toward N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), we found that Salmonella typhimurium LT2 sialidase (STSA) hardly cleaved 4-methylumbelliferyl Neu5Gc (4MU-Neu5Gc). The k cat/K m value of STSA for 4MU-Neu5Gc was found to be 110 times lower than that for 4-methylumbelliferyl Neu5Ac (4MU-Neu5Ac). Additionally, STSA had remarkably weak ability to cleave α2-3-linked-Neu5Gc contained in gangliosides and equine erythrocytes. In silico analysis based on first-principle calculations with transition-state analogues suggested that the binding affinity of Neu5Gc2en is 14.3 kcal/mol more unstable than that of Neu5Ac2en. The results indicated that STSA preferentially cleaves Neu5Ac residues rather than Neu5Gc residues, which is important for anyone using this enzyme to cleave α2-3-linked sialic acids.

Terminal sialic acids are an important determinant of pulmonary endothelial barrier integrity

The surface of vascular endothelium bears a glycocalyx comprised, in part, of a complex mixture of oligosaccharide chains attached to cell-surface proteins and membrane lipids. Importantly, understanding of the structure and function of the endothelial glycocalyx is poorly understood. Preliminary studies have demonstrated structural differences in the glycocalyx of pulmonary artery endothelial cells compared with pulmonary microvascular endothelial cells. Herein we begin to probe in more detail structural and functional attributes of endothelial cell-surface carbohydrates. In this study we focus on the expression and function of sialic acids in pulmonary endothelium. We observed that, although pulmonary microvascular endothelial cells express similar amounts of total sialic acids as pulmonary artery endothelial cells, the nature of the sialic acid linkages differs between the two cell types such that pulmonary artery endothelial cells express both α(2,3)- and α(2,6)-linked sialic acids on the surface (i.e., surficially), whereas microvascular endothelial cells principally express α(2,3)-linked sialic acids. To determine whether sialic acids play a role in endothelial barrier function, cells were treated with neuraminidases to hydrolyze sialic acid moieties. Disruption of cell-cell and cell-matrix adhesions was observed following neuraminidase treatment, suggesting that terminal sialic acids promote endothelial barrier integrity. When we measured transendothelial resistance, differential responses of pulmonary artery and microvascular endothelial cells to neuraminidase from Clostridium perfringens suggest that the molecular architecture of the sialic acid glycomes differs between these two cell types. Collectively our observations reveal critical structural and functional differences of terminally linked sialic acids on the pulmonary endothelium.

Extracellular electrical fields direct wound healing and regeneration

Endogenous DC electric fields (EFs) are important, fundamental components of development, regeneration, and wound healing. The fields are the result of polarized ion transport and current flow through electrically conductive pathways. Nullification of endogenous EFs with pharmacological agents or applied EFs of opposite polarity disturbs the aforementioned processes, while enhancement increases the rate of wound closure and the extent of regeneration. EFs are applied to humans in the clinic, to provide an overwhelming signal for the enhancement of healing of chronic wounds. Although clinical trials, spanning a course of decades, have shown that applied EFs enhance healing of chronic wounds, the mechanisms by which cells sense and respond to these weak cues remains unknown. EFs are thought to influence many different processes in vivo. However, under more rigorously controlled conditions in vitro, applied EFs induce cellular polarity and direct migration and outgrowth. Here we review the generation of endogenous EFs, the results of their alteration, and the mechanisms by which cells may sense these weak fields. Understanding the mechanisms by which native and applied EFs direct development and repair will enable current and future therapeutic applications to be optimized.

Cationic amphipathic peptides accumulate sialylated proteins and lipids in the plasma membrane of eukaryotic host cells

Cationic antimicrobial peptides (CAMPs) selectively target bacterial membranes by electrostatic interactions with negatively charged lipids. It turned out that for inhibition of microbial growth a high CAMP membrane concentration is required, which can be realized by the incorporation of hydrophobic groups within the peptide. Increasing hydrophobicity, however, reduces the CAMP selectivity for bacterial over eukaryotic host membranes, thereby causing the risk of detrimental side-effects. In this study we addressed how cationic amphipathic peptides—in particular a CAMP with Lysine–Leucine–Lysine repeats (termed KLK)—affect the localization and dynamics of molecules in eukaryotic membranes. We found KLK to selectively inhibit the endocytosis of a subgroup of membrane proteins and lipids by electrostatically interacting with negatively charged sialic acid moieties. Ultrastructural characterization revealed the formation of membrane invaginations representing fission or fusion intermediates, in which the sialylated proteins and lipids were immobilized. Experiments on structurally different cationic amphipathic peptides (KLK, 6-MO-LF11-322 and NK14-2) indicated a cooperation of electrostatic and hydrophobic forces that selectively arrest sialylated membrane constituents.

BgaA acts as an adhesin to mediate attachment of some pneumococcal strains to human epithelial cells

Streptococcus pneumoniae colonization of the respiratory tract is an essential precursor for pneumococcal disease. To colonize efficiently, bacteria must adhere to the epithelial-cell surface. S. pneumoniae possesses surface-associated exoglycosidases that are capable of sequentially deglycosylating human glycans. Two exoglycosidases, neuraminidase (NanA) and β-galactosidase (BgaA), have previously been shown to contribute to S. pneumoniae adherence to human epithelial cells, as deletion of either of these genes results in reduced adherence. It has been suggested that these enzymes may modulate adherence by cleaving sugars to reveal a receptor on host cells. Pretreatment of epithelial cells with exogenous neuraminidase restores the adherence of a nanA mutant, whereas pretreatment with β-galactosidase does not restore the adherence of a bgaA mutant. These data suggest that BgaA may not function to reveal a receptor, and implicate an alternative role for BgaA in adherence. Here we demonstrate that β-galactosidase activity is not required for BgaA-mediated adherence. Addition of recombinant BgaA (rBgaA) to adherence assays and pretreatment of epithelial cells with rBgaA both significantly reduced the level of adherence of the parental strain, but not the BgaA mutant. One possible explanation of these data is that BgaA is acting as an adhesin and that rBgaA is binding to the receptor, preventing bacterial binding. A bead-binding assay demonstrated that BgaA can bind directly to human epithelial cells, supporting the hypothesis that BgaA is an adhesin. Preliminary characterization of the epithelial-cell receptor suggests that it is a glycan in the context of a glycosphingolipid. To further establish the relevance of this adherence mechanism, we demonstrated that BgaA-mediated adherence contributed to adherence of a recent clinical isolate to primary human epithelial cells. Together, these data suggest a novel role for BgaA as an adhesin and suggest that this mechanism could contribute to adherence of at least some pneumococcal strains in vivo.

Sialivac: an intranasal homologous inactivated split virus vaccine containing bacterial sialidase for the control of avian influenza in poultry

A simple, effective inactivated avian flu vaccine composed of three homologous highly pathogenic (HP) H5N1 strains combined with Clostridium perfringens type A 107 sialidase/neuramindase and chitosan as a trans epithelial carrier adjuvant applied intranasally to poultry is described. Poultry were vaccinated with an inactivated, solvent split, chitosan adjuvanted intranasal (IN) vaccine with and without C. perfringens sialidase and the resulting serum IgG antibody measured by haemagglutination inhibition (HI) and mucosal IgA by ELISA. The clinical effectiveness was demonstrated by disease intervention field trials, where the ability of an intranasal vaccine containing three homologous inactivated solvent split HP H5N1 strains, C. perfringens sialidase and chitosan was successful in controlling the disease in intensively reared commercial chickens. Evidence is presented by demonstrating effective intervention with IN vaccine during outbreaks in poultry previously vaccinated with commercial heterologous H5N2 intramuscular (IM) vaccine and reassorted H5N1 Re-1 vaccine which had failed to protect intensively reared birds. Intervention with the IN vaccine in such flocks completely halted the infection within 2-5 days. Survivors ceased to excrete live virus. Stimulation of the common mucosal immune system (CMIS) and the early production of secretory IgA and subsequently humoral IgG demonstrated by laboratory controlled experiments and field studies revealed the ability of intranasally vaccinated birds to resist lethal virus challenge. A strategy of mucosal immunisation is recommended to reduce the incidence of disease in intensively reared poultry and thus minimise the generation and transfer of mutated highly pathogenic subtypes to humans and other animals.

Axon regeneration inhibitors

OBJECTIVE

To increase awareness of the advancements in nerve regeneration.

METHODS

Review of the literature regarding inhibitors of nerve outgrowth and presentation of potential agents that reverse the inhibition, thereby promoting nerve regeneration.

RESULTS

The injured adult central nervous system (CNS) inhibits axon outgrowth, thereby limiting recovery from traumatic injury. Axon regeneration inhibitors (ARIs) that contribute to inhibition of recovery include myelin-associated glycoprotein, Nogo, oligodendrocyte-myelin glycoprotein and chondroitin sulfate proteoglycans. The ARIs bind to specific receptors on the axon growth cone to halt outgrowth; consequently, reversing or blocking the actions of ARIs may promote recovery after CNS injury. Sialidase, an enzyme that cleaves one class of axonal receptors for myelin-associated glycoprotein, enhances spinal axon outgrowth into implanted peripheral nerve grafts in a rat model of brachial plexus avulsion, a traumatic injury in which nerve roots are torn from the spinal cord.

CONCLUSION

Repair using peripheral nerve grafts is a promising restorative surgical treatment in humans, although functional improvement remains limited. Molecular therapies targeting ARIs may aid functional recovery after brachial plexus avulsion or other nervous system injuries and diseases.

Real-time multi-site multi-parametric monitoring of rat brain subjected to traumatic brain injury

INTRODUCTION

Traumatic brain injury (TBI) is one of the major causes of death in the world, with at least ten million serious traumatic brain injuries occurring annually; nevertheless, the pathophysiologic events taking place immediately after the injury are not yet fully known.

OBJECTIVE

To study the effects of TBI on brain hemodynamic, metabolic and ionic homeostasis using the multi-parametric monitoring system. This system enables real-time monitoring of cerebral blood flow (CBF), mitochondrial NADH redox state, extracellular levels of K+, H+, DC potential, ECoG and ICP.

METHODS

In order to find the best brain location for the monitoring device in relation to the fluid percussion injury site, we used the multi-site multi-parametric monitoring system. Two groups of rats were connected to four monitoring probes at four different locations near the injury site, two in each hemisphere. We monitored CBF, NADH redox state, tissue reflectance and DC steady potential in each of the four sites.

RESULTS

Under anoxia, the initial CBF decrease was followed by an increase, NADH level increased, the reflectance decreased and dc potential showed a biphasic response, in all 4 locations. However, following fluid percussion injury, there was a significant variability in the responses in each of the 4 monitored locations.

CONCLUSION

The advantage of the multi-parametric-monitoring approach for enhanced understanding of the injured brain was indicated. Moreover, we showed that contralateral monitoring of the injured brain gives good indication for the events taking place following fluid percussion brain injury.

A new approach for mapping sialylated N-glycosites in serum proteomes

A new approach for proteome-wide analysis of sialylated N-glycopeptides based on the diagonal chromatographic COFRADIC technology is presented here. The use of alpha(2-3,6,8,9) neuraminidase is central to isolate sialylated N-glycopeptides out of a complex peptide mixture. Two different COFRADIC techniques are introduced here, either without or with post-metabolic oxygen-18 labeling (direct versus indirect sorting), and when applied to immuno-depleted mouse serum, we herewith identified 93 sialylated glycosylation sites in 53 serum proteins.

Role of sialic acid in bovine sperm–zona pellucida binding

Sperm binding activity has been detected in zona pellucida (ZP) glycoproteins and it is generally accepted that this activity resides in the carbohydrate moieties. In the present study we aim to identify some of the specific carbohydrate molecules involved in the bovine sperm-ZP interaction. We performed sperm binding competition assays, in vitro fecundation (IVF) in combination with different lectins, antibodies and neuraminidase digestion, and chemical and cytochemical analysis of the bovine ZP. Both MAA lectin recognising alpha-2,3-linked sialic acid and neuraminidase from Salmonella typhimurium with catalytic activity for alpha-2,3-linked sialic acid, demonstrated a high inhibitory effect on the sperm-ZP binding and oocyte penetration. These results suggest that bovine sperm-ZP binding is mediated by alpha-2,3-linked sialic acid. Experiments with trisaccharides (sialyllactose, 3'-sialyllactosamine and 6'-sialyllactosamine) and glycoproteins (fetuin and asialofetuin) corroborated this and suggest that at least the sequence Neu5Ac(alpha2-3)Gal(beta1-4)GlcNAc is involved in the sperm-ZP interaction. Moreover, these results indicate the presence of a sperm plasma membrane specific protein for the sialic acid. Chemical analysis revealed that bovine ZP glycoproteins contain mainly Neu5Ac (84.5%) and Neu5GC (15.5%). These two types of sialic acid residues are probably linked to Galbeta1,4GlcNAc and GalNAc by alpha-2,3- and alpha-2,6-linkages, respectively, as demonstrated by lectin cytochemical analysis. The use of a neuraminidase inhibitor resulted in an increased number of spermatozoa bound to the ZP and penetrating the oocyte. From this last result we hypothesize that a neuraminidase from cortical granules would probably participate in the block to polyspermy by removing sialic acid from the ZP.

Enhancement of CD8 T-cell function through modifying surface glycoproteins in young and old mice

Previous work from our laboratory has shown that modifying cell surface glycosylation with either a Clostridium perfringens-derived sialidase (CP-Siase), or an O-linked glycoprotein endopeptidase (OSGE) can enhance the function of CD4 T cells from both young and old mice at multiple levels. Here we have re-assessed the effect of age on CD8 T-cell function, and examined the outcome of enzymatic treatment with CP-Siase and OSGE on its different aspects. Pre-treatment of CD8 T cells with either CP-Siase or OSGE led to a significant increase in anti-CD3-mediated Ca2+ response in both young and old mice. Pre-treated CD8 T cells from both age groups also displayed a significant increase in activation-induced CD69 and CD25 expression, and produced significantly higher amounts of interleukin-2 and interferon-gamma in comparison to their untreated counterparts. Furthermore, pretreatment with either enzyme enhanced granzyme B expression in CD8 T cells, and increased their cytolytic activity in vitro. These data support the notion that glycosylated surface proteins hinder CD8 T-cell activation and function in both young and old mice, and raise the possibility of significantly improving CD8 T cell function in older individuals through enzymatic alteration of surface glycoproteins.

Sialidase enhances spinal axon outgrowth in vivo

The adult CNS is an inhibitory environment for axon outgrowth, severely limiting recovery from traumatic injury. This limitation is due, in part, to endogenous axon regeneration inhibitors (ARIs) that accumulate at CNS injury sites. ARIs include myelin-associated glycoprotein, Nogo, oligodendrocyte-myelin glycoprotein, and chondroitin sulfate proteoglycans (CSPGs). Some ARIs bind to specific receptors on the axon growth cone to halt outgrowth. Reversing or blocking the actions of ARIs may promote recovery after CNS injury. We report that treatment with sialidase, an enzyme that cleaves one class of axonal receptors for myelin-associated glycoprotein, enhances spinal axon outgrowth into implanted peripheral nerve grafts in a rat model of brachial plexus avulsion, a traumatic injury in which nerve roots are torn from the spinal cord. Repair using peripheral nerve grafts is a promising restorative surgical treatment in humans, although functional improvement remains limited. To model brachial plexus avulsion in the rat, C8 nerve roots were cut flush to the spinal cord and a peroneal nerve graft was inserted into the lateral spinal cord at the lesion site. Infusion of Clostridium perfringens sialidase to the injury site markedly increased the number of spinal axons that grew into the graft (2.6-fold). Chondroitinase ABC, an enzyme that cleaves a different ARI (CSPGs), also enhanced axon outgrowth in this model. In contrast, phosphatidylinositol-specific phospholipase C, which cleaves oligodendrocyte-myelin glycoprotein and Nogo receptors, was without benefit. Molecular therapies targeting sialoglycoconjugates and CSPGs may aid functional recovery after brachial plexus avulsion or other nervous system injuries and diseases.

Use of conformationally restricted pyridinium alpha-D-N-acetylneuraminides to probe specificity in bacterial and viral sialidases

Investigations into subtle changes in the catalytic activity of sialidases have been performed using enzymes from several different origins, and their results have been compared. This work highlights the potential pitfalls encountered when extending conclusions derived from mechanistic studies on a single enzyme even to those with high-sequence homology. Specifically, a panel of 5 pyridinium N-acetylneuraminides were used as substrates in a study that revealed subtle differences in the catalytic mechanisms used by 4 different sialidase enzymes. The lowest reactivity towards the artificial (pyridinium) substrates was displayed by the Newcastle disease virus hemagglutinin-neuraminidase. Moreover, in reactions involving aryl N-acetylneuraminides, the activity of the Newcastle enzyme was competitively inhibited by the 3,4-dihydro-2H-pyrano[3,2-c]pyridinium compound with a Ki = 58 micromol/L. Alternatively, the 3 bacterial enzymes tested, from Salmonella typhimurium, Clostridium perfringens, and Vibrio cholerae, were catalytically active against all members of the panel of substrates. Based on the observed effect of leaving-group ability, it is proposed that the rate-determining step for kcat (and likely for kcat/Km as well) with each bacterial enzyme is as follows: sialylation, which is concerted with conformational change for V. cholerae; and conformational change for S. typhimurium and C. perfringens.

A clostridial endo-beta-galactosidase that cleaves both blood group A and B glycotopes: the first member of a new glycoside hydrolase family, GH98

We have isolated an endo-beta-galactosidase designated E-ABase from Clostridium perfringens ATCC 10543 capable of liberating both the A trisaccharide (A-Tri; GalNAcalpha1-->3(Fucalpha1-->2)Gal) and B trisaccharide (B-Tri; Galalpha1-->3(Fucalpha1-->2)Gal) from glycoconjugates containing blood group A and B glycotopes, respectively. We have subsequently cloned the gene (eabC) that encodes E-ABase from this organism. This gene was found to be identical to the CPE0329 gene of C. perfringens strain 13, whose product was labeled as a hypothetical protein (Shimizu, T., Ohtani, K., Hirakawa, H., Ohshima, K., Yamashita, A., Shiba, T., Ogasawara, N., Hattori, M., Kuhara, S., and Hayashi, H. (2002) Proc. Natl. Acad. Sci. U. S. A. 99, 996-1001). Since the amino acid sequence of E-ABase does not bear detectable similarity to any of the 97 existing families of glycoside hydrolases, we have proposed to assign this unusual enzyme to a new family, GH98. We also expressed eabC in Escherichia coli BL21(DE3) and obtained 27 mg of fully active recombinant E-ABase from 1 liter of culture. Recombinant E-ABase not only destroyed the blood group A and B antigenicity of human type A and B erythrocytes, but also released A-Tri and B-Tri from blood group A(+)- and B(+)- containing glycoconjugates. The structures of A-Tri and B-Tri liberated from A(+) porcine gastric mucin and B(+) human ovarian cyst glycoprotein were established by NMR spectroscopy. The unique specificity of E-ABase should make it useful for studying the structure and function of blood group A- and B-containing glycoconju-gates as well as for identifying other glycosidases belonging to the new GH98 family.

Asialoglycoprotein receptor facilitates hemolysis in patients with alcoholic liver cirrhosis

Hemolysis in patients with advanced alcoholic liver disease is a common clinical problem and indicates an unfavorable prognosis. In many cases, the etiology of the hemolysis remains unknown. We observed three patients with alcoholic liver disease, suffering from severe hemolytic anemia, requiring multiple blood transfusions. Steroid therapy was ineffective and two of the patients died. All patients had a soluble variant of the human asialoglycoprotein receptor (s-ASGP-R) in their serum, as well as high titers of autoantibodies against this receptor (anti-ASGP-R). Consecutively, examination of 60 patients with alcoholic liver disease revealed a high incidence for s-ASGP-R (36%) and anti-ASGP-R (27%) in patients with alcoholic liver cirrhosis (ALC) compared to patients with cirrhosis due to viral hepatitis. The potential etiology of hemolysis was studied in vitro on erythrocytes from patients with ALC and from healthy donors. Isolated ASGP-R but not anti-ASGP-R bound to the surface of erythrocytes preferentially of blood group A1 and caused dose-dependent agglutination and hemolysis, while this phenomenon was much lower using erythrocytes of the blood group B and almost absent with blood group O-erythrocytes. Furthermore, agglutination and hemolysis only occurred in erythrocytes from ALC-patients or after the pre-treatment of cells with neuraminidase. ASGP-R induced agglutination and hemolysis was blocked by the competitive ASGP-R inhibitor asialofetuin. In conclusion, our results indicate a new, non-immunological mechanism for hemolysis in patients with alcoholic liver disease, mediated through agglutination by a soluble variant of the human asialoglycoprotein receptor and mechanical shear stress.

An integrity assay for a meningococcal type B conjugate vaccine

The development of an analytical procedure for the evaluation of a conjugate vaccine's structural wholeness or integrity is described. The principle component of the vaccine was the N-propionylated group B meningococcal polysaccharide (NPr-GBMP) covalently attached to a carrier protein. The goal of the procedure was to determine whether any whole polysaccharide, oligosaccharide, or monosaccharide, from minute to moderate levels, became detached off the conjugate. Free saccharide was isolated from the formulation, which included an aluminum hydroxide adjuvant for analysis. Due to its linkage, the NPr-GBMP did not release sialic acid efficiently with acid hydrolysis to the extent necessary for accurate quantitation. To accomplish depolymerization, the NPr-GBMP was subjected to methanolysis, 3N hydrochloric acid in methanol for 16h at 80 degrees C. The main product of the methanolysis reaction was a de-N-acylated methyl glycoside of sialic acid. N-acetylneuraminic acid oligomers and colominic acid were used to confirm the methanolysis depolymerization efficiency of the alpha(2 --> 8) saccharides; with the treatment all oligomers produced a common methyl glycoside. For this determination anion exchange chromatography and size exclusion chromatography were both interfaced to an integrated pulsed amperometric detector. Sensitivity and linearity were demonstrated to be sufficient for the application with vaccine dose formulations with low total saccharide concentrations.

alpha 2,3-Sialylation of terminal GalNAc beta 1-3Gal determinants by ST3Gal II reveals the multifunctionality of the enzyme. The resulting Neu5Ac alpha 2-3GalNAc linkage is resistant to sialidases from Newcastle disease virus and Streptococcus pneumoniae

Enzymatic alpha 2,3-sialylation of GalNAc has not been described previously, although some glycoconjugates containing alpha 2,3-sialylated GalNAc residues have been reported. In the present experiments, recombinant soluble alpha 2,3-sialyltransferase ST3Gal II efficiently sialylated the X(2) pentasaccharide GalNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc, globo-N-tetraose GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc, and the disaccharide GalNAc beta 1-3Gal in vitro. The purified products were identified as Neu5Ac alpha 2-3GalNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc, Neu5Ac alpha 2-3GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc, and Neu5Ac alpha 2-3GalNAc beta 1-3Gal, respectively, by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, enzymatic degradations, and one- and two-dimensional NMR-spectroscopy. In particular, the presence of the Neu5Ac alpha 2-3GalNAc linkage was firmly established in all three products by a long range correlation between Neu5Ac C2 and GalNAc H3 in heteronuclear multiple bond correlation spectra. Collectively, the data describe the first successful sialyltransfer reactions to the 3-position of GalNAc in any acceptor. Previously, ST3Gal II has been shown to transfer to the Gal beta 1-3GalNAc determinant. Consequently, the present data show that the enzyme is multifunctional, and could be renamed ST3Gal(NAc) II. In contrast to ST3Gal II, ST3Gal III did not transfer to the X(2) pentasaccharide. The Neu5Ac alpha 2-3GalNAc linkage of sialyl X(2) was cleaved by sialidases from Arthrobacter ureafaciens and Clostridium perfringens, but resisted the action of sialidases from Newcastle disease virus and Streptococcus pneumoniae. Therefore, the latter two enzymes cannot be used to differentiate between Neu5Ac alpha 2-3GalNAc and Neu5Ac alpha 2-6GalNAc linkages, as has been assumed previously.

A novel endo-beta-galactosidase from Clostridium perfringens that liberates the disaccharide GlcNAcalpha 1-->Gal from glycans specifically expressed in the gastric gland mucous cell-type mucin

We found that commercially available sialidases prepared from Clostridium perfringens ATCC10543 were contaminated with an endoglycosidase capable of releasing the disaccharide GlcNAcalpha1-->4Gal from glycans expressed in the gastric gland mucous cell-type mucin. We have isolated this enzyme in electrophoretically homogeneous form from the culture supernatant of this organism by ammonium sulfate precipitation followed by affinity chromatography using a Sephacryl S-200 HR column. The enzyme was specifically retained by and eluted from the column with methyl-alpha-Glc. By NMR spectroscopy, the structure of the disaccharide released from porcine gastric mucin by this enzyme was established to be GlcNAcalpha1-->4Gal. The specificity of this enzyme as an endo-beta-galactosidase was established by analyzing the liberation of GlcNAcalpha1-->4Gal from GlcNAcalpha1-->4Galbeta1-->4GlcNAcbeta1-->6(GlcNAcalpha1--> 4Galbeta1-->3)GalNAc-ol by mass spectrometry. Because this novel endo-beta-galactosidase specifically releases the GlcNAcalpha1-->4Gal moiety from porcine gastric mucin, we propose to call this enzyme a GlcNAcalpha1-->4Gal-releasing endo-beta-galactosidase (Endo-beta-Gal(GnGa)). Endo-beta-Gal(GnGa) was found to remove the GlcNAcalpha1-->4Gal epitope expressed in gastric adenocarcinoma AGS cells transfected with alpha1,4-N-acetylglucosaminyltransferase cDNA. Endo-beta-Gal(GnGa) should become useful for studying the structure and function of glycoconjugates containing the terminal GlcNAcalpha1-->4Gal epitope.

Integrin expression and IgA nephropathy: in vitro modulation by IgA with altered glycosylation and macromolecular IgA

BACKGROUND

Signal transduction by mesangial cell (MC) integrins regulates cell growth and survival, extracellular matrix production, and organization. The aim of the study was to investigate human MC integrin modulation by differently glycosylated IgA and macromolecular IgA, which are thought to play a pathogenetic role in IgA nephropathy (IgAN).

METHODS

MCs were incubated with purified human polymeric IgA, heat-aggregated IgA, IgA glycoforms generated by enzymatic hydrolysis of saccharide residues and serum fractions from IgAN patients, and controls isolated by lectin affinity and containing IgA with peculiar glycan patterns. Integrins were quantitated by flow cytometry.

RESULTS

Cultured MCs highly expressed alphavbeta3 and some alpha3beta1; alphavbeta3 was up-regulated by matrix components (P < 0.02). In vitro desialylated and degalactosylated polymeric human IgA enhanced alphavbeta3 expression on cultured MCs (P < 0.001). Serum IgA glycoforms isolated from IgAN patients with high exposure of internal sugars, GalNAc, Neu5Ac2,6GalNAc, and Man enhanced alphav expression on cultured MCs more than healthy controls. CONCLUSIONS.: These data support the hypothesis that IgA glycation plays a role in modulating the cell-matrix interaction, and that this mechanism can be operating in IgAN.

Synthesis of ganglioside GM1 containing a thioglycosidic bond to its labeled ceramide(s). A facile synthesis starting from natural gangliosides

Capitalizing on the readily available ganglioside, GM1, we have devised a simple synthesis of labeled GM1 analogues with sulfur in place of oxygen in their linkage to the ceramide residue (SGM1). The sugar moiety of ganglioside GM1 was released by ozonolysis and subsequent alkaline fragmentation in good yield. During acetylation of the ganglioside sugar, the carboxyl group of the sialic acid residue lactonized with the 2-hydroxyl group of the inner galactose moiety (galactose II). The resulting sialoyl-II2-lactone of pentadeca-O-acetyl-monosialogangliotetraose could be readily transformed into the alpha-glycosyl bromide. Subsequent treatment of this glycosyl bromide with potassium thioacetate afforded the sialoyl-II2-lactone of tetradeca-O-acetyl-1-S-acetyl-1-thio-beta-monosialogangliotetra ose. The latter could be condensed with (2R, 3R, 4E)-3-O-benzoyl-2-dichloroacetamido-1-iodo-4-octadecen -3-ol in methanolic sodium acetate to afford a protected lyso-SGM1 derivative. One-step removal of the protecting groups under alkaline conditions gave beta-monosialogangliotetraosyl thiosphingosine. This lyso-SGM1 was converted into labeled analogues of SGM1 using the N-succinimidoyl derivative of radiocarbon-labeled octanoic and octadecanoic acid, respectively. Subsequent actions of GM1-beta-galactosidase, beta-hexosaminidase A, sialidase and again GM1-beta-galactosidase on these labeled analogues of SGM1 in the presence of taurodeoxycholate produced the respective analogues of GM2, GM3, lactosylceramide and glucosylceramide, respectively.

Catalysis by a new sialidase, deaminoneuraminic acid residue-cleaving enzyme (KDNase Sm), initially forms a less stable alpha-anomer of 3-deoxy-D-glycero-D-galacto-nonulosonic acid and is strongly inhibited by the transition state analogue, 2-deoxy-2, 3-didehydro-D-glycero-D-galacto-2-nonulopyranosonic acid, but not by 2-deoxy-2,3-didehydro-N-acetylneuraminic acid

Deaminoneuraminic acid residue-cleaving enzyme (KDNase Sm) is a new sialidase that has been induced and purified from Sphingobacterium multivorum. Catalysis by this new sialidase has been studied by enzyme kinetics and 1H NMR spectroscopy. Vmax/Km values determined for synthetic and natural substrates of KDNase Sm reveal that 4-methylumbelliferyl-KDN (KDNalpha2MeUmb, Vmax/Km = 0.033 min-1) is the best substrate for this sialidase, presumably because of its good leaving group properties. The transition state analogue, 2, 3-didehydro-2,3-dideoxy-D-galacto-D-glycero-nonulosonic acid, is a strong competitive inhibitor of KDNase Sm (Ki = 7.7 microM versus Km = 42 microM for KDNalpha2MeUmb). 2-Deoxy-2, 3-didehydro-N-acetylneuraminic acid and 2-deoxy-2, 3-didehydro-N-glycolylneuraminic acid are known to be strong competitive inhibitors for bacterial sialidases such as Arthrobacter ureafaciens sialidase; however, KDNase Sm activity is not significantly inhibited by these compounds. This observation suggests that the hydroxyl group at C-5 is important for recognition of the inhibitor by the enzyme. Reversible addition of water molecule (or hydroxide ion) to the reactive sialosyl cation, presumably formed at the catalytic site of KDNase Sm, eventually gives rise to two different adducts, the alpha- and beta-anomers of free 3-deoxy-D-glycero-D-galacto-nonulosonic acid. 1H NMR spectroscopic studies clearly demonstrate that the thermodynamically less stable alpha-form is preferentially formed as the first product of the cleavage reaction and that isomerization rapidly follows, leading to an equilibrium mixture of the two isomers, the beta-isomer being the major species at equilibrium. Therefore, we propose that KDNase Sm catalysis proceeds via a mechanism common to the known exosialidases, but the recognition of the substituent at C-5 by the enzyme differs.

Diversity in the properties of two sialidase isoenzymes produced by Clostridium perfringens spp

Clostridium perfringens produces two sialidases, one of which has a molecular mass of 71 kDa and is secreted, while the 'small', 43 kDa isoenzyme remains in the cells. The secreted, higher molecular mass sialidases of two different clostridial strains, DSM756T and A99, exhibit maximum activity at pH 5.5 and at 51 or 55 degrees C, respectively. The molecular mass of both enzymes is 71 kDa in SDS-PAGE and 63 kDa as determined by gel-filtration, which indicates the absence of subunits. Natural sialidase substrates are hydrolyzed at comparably high rates, e.g. the glycoproteins fetuin and bovine submandibular gland mucin, the homopolymer colominic acid, and the ganglioside mixture from bovine brain. The partially purified 'small' isoenzyme from C. perfringens A99 cells had similar properties to the corresponding recombinant sialidase isolated from the Escherichia coli host. It is located inside the clostridial and E. coli cells and exhibits maximum activity at pH 6.1 and 37 degrees C. A relative molecular mass of 32,000 was found with FPLC gel-filtration chromatography, while primary structure analysis yielded a value of 43,000. It differs a significantly from the 'large' isoenzyme by substrate specificity. Preferred substrates are oligosaccharides, while other, more complex sialoglycoconjugates are hydrolyzed only at very low rates. alpha 2,3-linkages are hydrolyzed much faster than alpha 2,6-bonds.

Differential glycosylation of auditory and vestibular hair bundle proteins revealed by peanut agglutinin

Up to four morphologically distinct types of cross-link are found between the stereocilia in the hair bundles of avian hair cells. These links are involved in mechanotransduction, force transmission across the bundle, and maintenance of hair bundle structure. They appear to be specialisations of the cell coat, but very little is known about their molecular composition. Chick inner ear tissues were therefore screened with a number of different lectins to find markers for specialisations of the hair bundle surface. One lectin, peanut agglutinin (PNA), which recognises the dissacharide Gal beta 1-3GalNAc, was found to be a fairly selective marker for vestibular hair bundles, but it does not stain the stereocilia of auditory hair cells. The staining patterns observed with PNA in the vestibular system closely resemble those seen with a monoclonal antibody (mab) directed against a 275 kD component of the hair cell's apical surface known as the hair-cell antigen (HCA). However, unlike PNA, the mab recognises both vestibular and auditory hair cells. A detailed comparison of the fluorescence staining patterns observed with PNA and the anti-HCA mab indicates that binding sites for both ligands spatially codistribute on the surface of vestibular hair cells. The lectin and the anti-HCA mab binding sites are both sensitive to trypsin treatment, and, with sections of the vestibular system, PNA pretreatment blocks subsequent anti-HCA mab staining. Immunoelectron microscopy of vestibular hair bundles shows that PNA and the anti-HCA mab both label a type of cross-link known as the shaft connector. This link type is present on both auditory and vestibular hair bundles but reacts with PNA only in the vestibular system. The lectin jacalin, which has greater specificity for Gal beta 1-3GalNAc than does PNA, also only labels vestibular and not auditory hair bundles. Although terminal sialic acid residues can block both PNA and jacalin binding, neuraminidase treatment does not unmask cryptic binding sites for these lectins on auditory hair cells but does reveal PNA and jacalin staining at a number of other locations in the inner ear. The results obtained with the lectins PNA and jacalin indicate that either the HCA or other components of the shaft links are differentially glycosylated in the vestibular and auditory epithelia of the bird. The functional significance for such a difference in glycosylation remains to be determined, but auditory and vestibular hair cells operate over different frequency ranges, and variations in glycosylation might confer different micromechanical properties on the hair bundles in these two systems.

Estimation of gold-labelled macromolecules attached to cell surfaces

A method for obtaining a semi-quantitative estimation of the amount of colloidal gold label attached to a cell surface is described. The X-ray emission, in a scanning electron microscope, from an even metal coating applied by diode sputter coating is used as an internal standard. The emission from the standard is used to correct for errors which would have arisen due to factors such as variable specimen surface topography. Examples of the semi-quantitative estimation of 10-nm gold-labelled wheat-germ agglutinin to L929 murine fibroblast cells are given.

Mitogenic effects of bacterial neuroaminidase and lactosylceramide on human cultured fibroblasts

Exogenously added bacterial neuraminidase and lactosylceramide both stimulated the growth of cultured human skin fibroblasts. Neuraminidase (100 units/ml) increased DNA synthesis 1.9-fold and cell density 1.4-fold after 24 and 48 h, respectively, in culture. Treated fibroblasts contained less ganglioside NeuAc alpha 2-3Gal beta 1-4GlcCer (GM3), presumably due to neuraminidase-catalyzed hydrolysis to lactosylceramide. Addition of lactosylceramide (100 microM) to the fibroblast culture medium also increased DNA synthesis threefold within 24 h and cell density twofold after 48 h. These findings are compatible with a mechanism by which the proliferation of human fibroblasts is regulated by the relative levels of GM3 and lactosylceramide in the plasma membrane.

Immobilized enzyme system for determination of sialic acid in serum or urine

An immobilized enzyme system has been developed and employed to determine the concentration of sialic acid (N-acetylneuraminic acid) in human serum and urine. Two enzyme pairs, neuramindiase-Neu-5-Ac lyase and pyruvate oxidase-peroxidase, have been respectively co-immobilized onto 1,12-aminododecane-agarose with glutaraldehyde. The relative specific activity of the co-immobilized neuraminidase and Neu-5-Ac lyase were 60% and 78%, and those of pyruvate oxidase and peroxidase were 50% and 95% of the corresponding soluble enzymes, respectively. The optimal reaction pH at 37 degrees C for each of the co-immobilized enzymes was about one pH unit higher than that of the corresponding soluble enzyme. The optimal reaction temperature of each enzyme was increased as a result of immobilization. The thermal stability at 45 degrees C of the immobilized neuraminidase, Neu-5-Ac lyase, pyruvate oxidase, and peroxidase were increased 80-, 83-, 115-, and 147-fold, respectively. Km and Vm of each immobilized and co-immobilized enzyme have also been determined. The system provided a convenient and rapid method to determine the concentration of total sialic acid without pretreatment of the sample. The results correlated satisfactorily with those obtained by using a soluble enzyme system. The co-immobilized enzymes were stable for at least 1 year of 500 tests when used repeatedly. The system is thus a reproducible and reliable novel assay method for sialic acid in the serum or urine sample.

Carbohydrate analysis of glycoproteins. A review

Many of the products prepared by biotechnological approaches, including recombinant genetic engineering, cell tissue culture, and monoclonal technologies, are glycoproteins. As little as five years ago, glycosylation was believed to play no significant role in the function of glycoproteins. Recent large scale testing of glycoprotein-based pharmaceuticals has indicated that both the extent and type of glycosylation can play a central role in glycoprotein activity. Although methods for compositional and sequence analysis of proteins and nucleic acids are generally available, similar methods have yet to be developed for carbohydrate oligomers and polymers. This review focuses on new, developing methods for the analysis and sequencing of the carbohydrate portion of glycoproteins. Included are: (1) the release of oligosaccharides and hydrolysis of carbohydrate chains using enzymatic and chemical methods; (2) fractionation by LPLC, electrophoresis, HPLC, and lectin affinity chromatography; (3) detection through the preparation of derivatives or by new electrochemical methods; (4) analysis by spectroscopic methods, including MS and high-field NMR; and (5) their sequencing through the use of multiple, well-integrated techniques. The ultimate goal of the analytical approaches discussed is to firmly establish structure and, thus, permit the study of structure-function relationships and eventually to allow the intelligent application of carbohydrate remodeling techniques in the preparation of new glycoproteins.

Bovine testicular beta-galactosidase: purification of enzyme fractions that exhibit high affinity for phosphomannosyl receptors

An improved method is described for the preparation of bovine testicular beta-galactosidase that allows the isolation of enzyme fractions that bind avidly to phosphomannosyl receptors. The procedure permits removal of a contaminating beta-hexosaminidase and yields nearly homogeneous beta-galactosidase. Enzyme eluted from DEAE-Sephacel was arbitrarily divided into pools that exhibited differing ability to bind phosphomannosyl receptors. A high binding fraction was rapidly assimilated by cultured cells and bound to both low and high molecular weight phosphomannosyl receptors. Carbohydrate analysis of the high binding fraction indicates an average content of one complex and one high mannose oligosaccharide chain per molecule and an average mannose 6-phosphate content of two residues per molecule. However, electrofocusing studies indicated that all the fractions were heterogeneous with respect to sialic acid and phosphate content. The purification procedure also provides highly purified beta-galactosidase suitable for removing beta-galactosidase residues from a variety of complex carbohydrates.

Curvature and composition-dependent lipid asymmetry in phosphatidylcholine vesicles containing phosphatidylethanolamine and gangliosides

The effect of curvature on transbilayer lipid asymmetry in vesicles is investigated using vesicles of different sizes (30-140 nm) prepared by sonication and polycarbonate filter extrusion techniques. The transbilayer distributions of phosphatidylethanolamine and gangliosides are measured using 2,4,6-trinitrobenzenesulphonic acid and Clostridium perfringens neuraminidase as non-penetrating probes, respectively. The distribution of phosphatidylethanolamine in a phosphatidylcholine/phosphatidylethanolamine (4:1, molar ratio) system is more or less symmetric and curvature seems to have little effect. However, the distribution of gangliosides in a phosphatidylcholine/ganglioside (10:1, molar ratio) system is asymmetric in favour of the outer layer in smaller vesicles, the asymmetry disappearing as the degree of curvature decreases. In a phosphatidylcholine/phosphatidylethanolamine/ganglioside (8:2:1, molar ratio) system, both phosphatidylethanolamine and gangliosides distribute asymmetrically, indicating a composition-dependent asymmetric distribution of phosphatidylethanolamine. In this system asymmetry also increases with increasing curvature. The asymmetric distribution of gangliosides in vesicles of low curvature may be due to their long headgroup and larger headgroup surface area in accordance with the theoretical predictions of Israelachvili et al. (Biochim. Biophys. Acta 470 (1977) 185-201).