Structures and functions of the sugar chains of glycoproteins

A new beta-1,2-N-acetylglucosaminyltransferase that may play a role in the biosynthesis of mammalian O-mannosyl glycans

Recent studies have shown that O-mannosyl glycans are present in several mammalian glycoproteins. Although knowledge on the functional roles of these glycans is accumulating, their biosynthetic pathways are poorly understood. Here we report the identification and initial characterization of a novel enzyme capable of forming GlcNAc beta 1-2Man linkage, namely UDP-N-acetylglucosamine: O-linked mannose beta-1,2-N-acetylglucosaminyltransferase in the microsome fraction of newborn rat brains. The enzyme transfers GlcNAc to beta-linked mannose residues, and the formed linkage was confirmed to be beta 1-2 on the basis of diplococcal beta-N-acetylhexosaminidase susceptibility and by high-pH anion-exchange chromatography. Its activity is linearly dependent on time, protein concentration, and substrate concentration and is enhanced in the presence of manganese ion. Its activity is not due to UDP-N-acetylglucosamine: alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GnT-I) or UDP-N-acetylglucosamine: alpha-6-D-mannoside beta-1,2-D-acetylglucosaminyltransferase II (GnT-II), which acts on the early steps of N-glycan biosynthesis, because GnT-I or GnT-II expressed in yeast cells did not show any GlcNAc transfer activity against a synthetic mannosyl peptide. Taken together, the results suggest that the GlcNAc transferase activity described here is relevant to the O-mannosyl glycan pathway in mammals.

Site-directed mutagenesis of heparin-binding EGF-like growth factor (HB-EGF): analysis of O-glycosylation sites and properties

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a 22 kDa, O-glycosylated protein. HeLa cells infected with a recombinant vaccinia virus expressing human HB-EGF produced a secreted, bioactive protein, with Mr 22,000 that was decreased to 14,000 by treatment with O-glycanase. Site-directed mutagenesis of HB-EGF cDNA using oligonucleotide- and PCR-directed techniques was performed to change the potential glycosylation sites, Thr75 and Thr85, to alanine residues to prevent O-glycosylation. Purification and characterization of the mutant proteins demonstrated that: (i) both O-glycosylation sites of HB-EGF are utilized, (ii) HB-EGF secretion does not require O-glycosylation, (iii) removal of O-glycans does not affect proteolytic cleavage of the HB-EGF precursor, nor does it influence HB-EGF intracellular trafficking or subcellular localization, and (iv) HB-EGF produced by HeLa cells is heavily sialylated. Comparisons between glycosylation mutants and wild-type HB-EGF revealed no significant apparent differences in receptor binding activity.

Analytical Application of Oligopyrrole Macrocycles

Progress of modern analytical chemistry is closely related with advancement in other fields such as organic chemistry and biochemistry. Successful solution of current scientific problems is inconceivable without close cooperation of different chemical disciplines. As an example of such hot and very intricate theme research in the field of molecular recognition of biologically active compounds can serve, where numerous methods of analytical chemistry, organic chemistry and biochemistry can suitably be utilized, elaborated and brought into consonance. This multidisciplinary overlap logically leads to the advent of new scientific fields with their own tools, methodologies and subjects of exploration - bioanalytical chemistry and nanotechnology. This review covers different aspects of analytical application of oligopyrrole macrocycles (mainly porphyrins and sapphyrins). These compounds are widely used in analytical chemistry due to their outstanding optical properties. In our contribution oligopyrrole macrocycles are considered as signaling and structural parts of chemical receptors and selectors in various applications. Introduction of different moieties into meso-position of macrocyclic rings allows to obtain e.g., sterically well-organized receptors for recognition of biologically important analytes, new chromatographic materials, and powerful tools in electrochemical research. Finally, future trends in the field are outlined briefly.

Both cell-surface carbohydrates and protein tyrosine phosphatase are involved in the differentiation of astrocytes in vitro

Astrocytes are important in the development and maintenance of functions of the CNS, acting in cooperation with neurons and other glial cells. The glycans on astrocyte membrane are believed to play important roles in cell-cell communication. Plant lectins are useful probes, because the lectins can bind to certain cell surface receptors and elicit cellular responses that are normally activated by endogenous ligands for those receptors. In the present study, we investigated the effect of Datura stramonium agglutinin (DSA) on astrocytes and characterized several molecular events. The addition of DSA to a culture of flat, polygonal, immature astrocytes derived from the neonatal rat cerebellum caused the cells to become stellate in shape, similar to astrocytes observed in vivo, concomitant with an increase in expression of astrocyte-specific intermediate filament (glial fibrillary acidic protein [GFAP]) and inhibition of proliferation. These results indicate that DSA binds to astrocytes and triggers differentiation. We also found a decrease in the extent of tyrosine-phosphorylation of a 38-kDa protein. To elucidate the molecular events during astrocyte differentiation, we examined the effects of various signal transduction inhibitors on the transformation from the polygonal to stellate shape (stellation). Interestingly, only tyrosine phosphatase inhibitors, orthovanadate and phenylarsine oxide, showed an inhibitory effect. Our results suggest that DSA induced astrocyte differentiation acts via tyrosine dephosphorylation.

Preparation and structure determination of two sugar amino acids via corresponding hydantoin derivatives

(4R)-2,3-O-Isopropylidene-methylspiro[4,6-dideoxy-alpha-L-lyxo+ ++-hexopyranosid-4,5'-imidazolidin]-2',4'-dione and (4R)-2,3-O-isopropylidene-methylspiro[4,6-dideoxy-beta-D-ribo-h exopyranosid-4,5'-imidazolidin]-2',4'-dione were prepared under various reaction conditions starting from methyl 6-deoxy-2,3-O-isopropylidene-alpha-L-lyxo-hexopyranosid-4-++ +ulose. Corresponding alpha-amino acids methyl (4R)-4-amino-4-C-carboxy-4,6-dideoxy-alpha-L-lyxo-hexopyranosid e and methyl (4R)-4-amino-4-C-carboxy-4,6-dideoxy-beta-D-ribo-hexopyranoside were obtained from the above hydantoins by selective acid hydrolysis of the isopropylidene group, followed by basic hydrolysis of the hydantoin ring. The crystal structures of both hydantoin derivatives are also presented.

Genomic structure and promoter analysis of the human alpha1, 6-fucosyltransferase gene (FUT8)

GDP-L-Fuc:N-acetyl-beta-D-glucosaminide alpha1,6-fucosyltransferase (alpha1,6FucT) catalyzes the transfer of a fucosyl moiety from GDP-fucose to the asparagine-linked GlcNAc residue of complex N-glycans via alpha1,6-linkage. We have cloned the genomic DNA which encodes the human alpha1,6FucT gene ( FUT8 ) and analyzed its structure. It was found that the gene consists of at least nine exons spanning more than a 50 kbp genomic region, and the coding sequence is divided into eight exons. The translation initiation codon was located at exon 2, and thus exon 1 encodes only 5'-untranslated sequences. Transcription initiation site of FUT8 was determined by 5'-rapid amplification of the cDNA end and a primer-extension analysis using the total RNA isolated from SK-OV-3 cells, which have a high level of alpha1,6FucT activity. We then characterized the FUT8 promoter region by a reporter gene assay. The luciferase reporter assay indicated that the 5'-flanking region of exon 1, which covered about 1 kbp, conferred the promoter activity in SK-OV-3 cells. This region contains potential binding sites for some transcription factors, such as bHLH, cMyb, GATA-1, as well as a TATA-box, but not a CCAAT motif. 5'-Untranslated sequences found in ESTs and the cDNA for the FUT8 suggest the presence of an additional exon(s) at the upstream of the first exon identified in this study, and therefore, the transcription of the gene would be regulated by multiple promoters.

Glycocalyx modulation is a physiological means of regulating cell adhesion

Here we present experimental evidence that phagocytic cells use modulation of specific components of their glycocalyx to regulate their binding capacity. Particles coated with antibodies specific for the CD32 medium affinity IgG receptor were driven along human monocytic THP-1 cells (expressing CD32) in a flow chamber operated at low shear rate. Surprisingly, only minimal adhesion was observed. However, when cells were activated by exposure to fibronectin-coated surfaces and/or soluble γ interferon, adhesion efficiency was dramatically increased, whereas the apparent glycocalyx thickness displayed 20% decrease, and the surface density of CD43/leukosialin carbohydrate epitopes displayed 30–40% decrease on activated cells. The existence of a causal link between adhesion increase and glycocalyx alteration was strongly supported by the finding that (i) both phenomena displayed similar kinetics, (ii) an inverse relationship between THP-1 cell binding capacity and glycocalyx density was demonstrated at the individual cell level, and (iii) adhesion enhancement could not be ascribed to an increased binding site density or improved functional capacity of activated cells. Additional experiments revealed that cell-to-particle adhesion resulted in delayed (i.e. more than a few minutes) egress of CD43/leukosialin from contact areas. Since the time scale of particle attachment was less than a second, surface mobility should not affect the potential of CD43 to impair the initial step of adhesion. Finally, studies performed with fluorescent lectins suggested that THP-1 cell activation and increased adhesive potential were related to a decrease of O-glysosylation rather than N-glycosylation of surface glycoproteins.

Remodeling of sugar chain structures of human interferon-gamma

Natural human interferon (IFN)-gamma has mainly biantennary complex-type sugar chains and scarcely has multiantennary structures. We attempted to remodel the sugar chain structures using IFN-gamma as a model glycoprotein. To obtain the branching glycoforms of IFN-gamma, we introduced the genes for GnT-IV (UDP-N-acetylglucosamine:alpha-1,3-D-mannoside beta-1, 4-N-acetylglucosaminyltransferase) and/or GnT-V (UDP-N-acetylglucosamine:alpha-1,6-D-mannoside beta-1, 6-N-acetylglucosaminyltransferase) into Chinese hamster ovary (CHO) cells producing human IFN-gamma. The parental CHO cells produced IFN-gamma with biantennary sugar chains mainly. When the GnT-IV activity was increased, triantennary sugar chains with a branch produced by GnT-IV increased up to 66.9% of the total sugar chains. When the GnT-V activity was increased, triantennary sugar chains with a corresponding branch increased up to 55.7% of the total sugar chains. When the GnT-IV and -V activities were increased at a time, tetraantennary sugar chains increased up to 56.2% of the total sugar chains. The proportion of these multiantennary sugar chains corresponded to the intracellular activities of GnT-IV and -V. What is more, lectin blot and flow cytometric analysis indicated that the multi-branch structure of the sugar chains was increased not only on IFN-gamma, one of the secretory glycoproteins, but also on almost CHO cellular proteins by introducing either or both of the GnT genes. The results suggest that the branching structure of sugar chains of glycoproteins could be controlled by cellular GnT-IV and GnT-V activities. This technology can produce glycoforms out of natural occurrence, which should enlarge the potency of glycoprotein therapeutics.

Independent and hetero-oligomeric-dependent sperm binding to egg envelope glycoprotein ZPC in Xenopus laevis

Vitelline envelopes are composed of glycoproteins that participate in sperm-egg interactions during the initial stages of fertilization. In Xenopus laevis, the vitelline envelope is composed of at least 4 glycoproteins (ZPA, ZPB, ZPC, and ZPX). A sperm binding assay involving the covalent coupling of envelope glycoproteins to silanized glass slides was developed. In our assay, sperm bound to the egg envelopes derived from oviposited eggs but not activated eggs. The majority of the egg envelope ligand activity for sperm binding was derived from the complex N-linked oligosaccharides of ZPC. This sperm binding involved N-acetylglucosamine and fucose residues, as binding was abolished after treatment with cortical granule beta-N-acetylglucosaminidase and commercial beta-N-acetylglucosaminidases and was reduced by 44% after treatment with alpha-fucosidase. Although both the envelope glycoproteins ZPA and ZPC possessed independent ligand activity, ZPC was the major ligand for sperm binding (75%). Mixing of isolated ZPA, ZPB, and ZPC in a ratio of 1:4:4 (equal to that in the egg envelope) resulted in sperm binding that was greater than that of the sum of the separate components. The egg glycoproteins acted in synergy to increase sperm binding. Thus, ZPC possessed both independent and hetero-oligomeric-dependent ligand activities for sperm binding.

N-Linked glycans of proteins from mitral valves of normal pigs and pigs affected by endocardiosis

Endocardiosis, a degenerative and dystrophic process affecting cardiac valves and described in many mammalian species, is characterized by the accumulation of glycosaminoglycans, in particular hyaluronic acid, in the extracellular matrix. The glycoprotein patterns of pig mitral valves in normal animals and animals affected by endocardiosis were investigated. A different N-linked glycosylation pattern of glycoproteins was detected in affected valves compared with normal ones. In either normal or pathological species, the detected N-linked glycans were of the complex type. However, in samples from affected valves, sialic acid showed a prevalence of the alpha2,6 linkage to the galactosyl residue, whereas in normal samples the most frequent linkage was of the alpha2,3 type. In normal valves, the majority of complex oligosaccharides presented two outer branches with different degrees of fucosylation and sialylation, whereas in pathological samples we noted an increased number of glycans having up to four outer branches.

Changes in glycosylation of rat liver arylsulfatase B in relation to age

The aim of this study was to determine how glycosylation of the rat liver arylsulfatase B was influenced by the age of the animal. The enzyme was purified from a liver lysosomal fraction obtained from male Wistar rats aged 18 days of gestation, 1 week, and 1, 1.5, 3 and 18 months by an affinity chromatography. Examination of the carbohydrate structures was performed after electrophoresis and blotting, followed by a very sensitive detection system with a set of six highly specific digoxygenin-labelled lectins. After densitometric measurement of the intensity of a digoxigenin-labelled lectin binding to arylsulfatase B, it could be stated that, at least, changes in sialylation are related to the growth and development of rats. Sialylation increases while fucosylation slightly decreases with age of the animal.

The cytoplasmic, transmembrane, and stem regions of glycosyltransferases specify their in vivo functional sublocalization and stability in the Golgi

We provide evidence for the presence of targeting signals in the cytoplasmic, transmembrane, and stem (CTS) regions of Golgi glycosyltransferases that mediate sorting of their intracellular catalytic activity into different functional subcompartmental areas of the Golgi. We have constructed chimeras of human alpha1, 3-fucosyltransferase VI (FT6) by replacement of its CTS region with those of late and early acting Golgi glycosyltransferases and have stably coexpressed these constructs in BHK-21 cells together with the secretory reporter glycoprotein human beta-trace protein. The sialyl Lewis X:Lewis X ratios detected in beta-trace protein indicate that the CTS regions of the early acting GlcNAc-transferases I (GnT-I) and III (GnT-III) specify backward targeting of the FT6 catalytic domain, whereas the CTS region of the late acting human alpha1,3-fucosyltransferase VII (FT7) causes forward targeting of the FT6 in vivo activity in the biosynthetic glycosylation pathway. The analysis of the in vivo functional activity of nine different CTS chimeras toward beta-trace protein allowed for a mapping of the CTS donor glycosyltransferases within the Golgi/trans-Golgi network: GnT-I < (ST6Gal I, ST3Gal III) < GnT-III < ST8Sia IV < GalT-I < (FT3, FT6) < ST3Gal IV < FT7. The sensitivity or resistance of the donor glycosyltransferases toward intracellular proteolysis is transferred to the chimeric enzymes together with their CTS regions. Apparently, there are at least three different signals contained in the CTS regions of glycosyltransferases mediating: first, their Golgi retention; second, their targeting to specific in vivo functional areas; and third, their susceptibility toward intracellular proteolysis as a tool for the regulation of the intracellular turnover.

Fucose in N-glycans: from plant to man

Fucosylated oligosaccharides occur throughout nature and many of them play a variety of roles in biology, especially in a number of recognition processes. As reviewed here, much of the recent emphasis in the study of the oligosaccharides in mammals has been on their potential medical importance, particularly in inflammation and cancer. Indeed, changes in fucosylation patterns due to different levels of expression of various fucosyltransferases can be used for diagnoses of some diseases and monitoring the success of therapies. In contrast, there are generally at present only limited data on fucosylation in non-mammalian organisms. Here, the state of current knowledge on the fucosylation abilities of plants, insects, snails, lower eukaryotes and prokaryotes will be summarised.

O-mannosyl glycans in mammals

Most proteins within living organisms contain glycans. Glycan structures can modulate the biological properties and functions of glycoproteins. The major glycans of glycoproteins can be classified into two groups, N-glycans and O-glycans, according to their glycan-peptide linkage regions. Developments in glycobiology have revealed a new type of glycosidic linkage to the peptide portion, the O-mannosyl linkage, in mammals, while so far it had been thought to be specific to yeast. This review will give an outline of the O-mannosyl glycans of mammalian glycoproteins. Since one of the most well known O-mannosyl-modified mammalian glycoproteins is dystroglycan, the functional aspects of the O-mannosyl glycan of dystroglycan will be described to help understand this new glycobiological field.

Intracellular lectins associated with N-linked glycoprotein traffic

The vectorial intracellular transport of N-glycan-linked glycoproteins is indispensable for biological functions. In order to sort these glycoproteins to the correct destination, animal intracellular lectins play important roles as sorting receptors. The roles of such lectins in the biosynthetic pathway from the endoplasmic reticulum (ER) to the cell surface are addressed in this review. Calnexin and calreticulin function via specific carbohydrates in quality control of newly synthesized glycoproteins in the ER, and ERGIC-53 seems to function in the transport of glycoproteins from ER to the Golgi complex. In addition to the well-understood role of mannose 6-phosphate receptor in lysosomal protein sorting, the vesicular integral protein of 36 kDa (VIP36) functions as a sorting receptor by recognizing high-mannose type glycans containing alpha1-->2Man residues for transport from Golgi to the cell surface in polarized epithelial cells.

Recombinant glycoprotein product quality in proliferation-controlled BHK-21 cells

We analyzed product quality to determine the applicability of proliferation-controlled mammalian cells for recombinant pharmaceutical protein production. Baby hamster kidney (BHK)-21 cells were engineered to express a dicistronic, stabilized, self-selecting growth control system consisting of a beta-estradiol-activatable transcription factor IRF-1 fusion protein. IRF-1 activity led to a reduced growth rate, whereas productivity, protein integrity, and glycosylation pattern of the industrially relevant secreted pharmaceutical glycoprotein erythropoietin remained consistent, showing that this technique has the potential for improving the consistency of high-quality pharmaceutical products and thus warrants further development.

Sialoforms of dipeptidylpeptidase IV from rat kidney and liver

Dipeptidylpeptidase IV (DPP IV, CD26), a serine-type exo- and endopeptidase found in the cell surface membrane of many tissues, was employed as a model membrane glycoprotein to study the expression of sialoforms on cell surface glycoproteins. Native, enzymatically active DPP IV was purified from plasma membranes of kidney and liver by lectin affinity chromatography in conjunction with crown ether anion exchange chromatography. The enzyme was gradient-eluted in continuous fractions, all showing a single polypeptide band of about 100 kDa when separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing, denaturing conditions. Analysis of the purified DPP IV by isoelectric focusing (IEF) showed that it consists of several polypeptides of different isoelectric points (IP) ranging from 5.5 to 7.0. In vitro- desialylation of the enzyme and subsequent isoelectric focusing revealed that the differences in isoelectric points were due to differences in the degree of sialylation. Differences in the degree of sialylation between the fractions were also demonstrated by SDS-PAGE under nonreducing and nondenaturing conditions. Increased sialylation of the enzyme as demonstrated by isoelectric focusing resulted in increased migration velocity in nonreducing and nondenaturing SDS-polyacrylamide gels. In vitro -desialylation of the enzyme and its resialylation confirmed that sialylation was responsible for this extraordinary migration behavior. The native enzyme was predominantly sialylated via alpha 2, 6-linkage, as shown by lectin affinity blotting employing Sambucus nigra agglutinin (SNA) and Maackia amurensis agglutinin (MAA). These findings demonstrate that a distinct membrane glycoprotein may exist in various sialoforms, distinguished from each other by a different number of sialic acid residues. Moreover, these sialoforms can be individually purified by crown ether anion exchange chromatography.

Carbohydrate analysis of a chimeric recombinant monoclonal antibody by capillary electrophoresis with laser-induced fluorescence detection

A general method for the analysis of asparaginyl-linked (N-linked) carbohydrate moieties of an IgG1 monoclonal antibody is described here. The antibody, rituximab, is a mouse/human chimeric antibody to human CD20 antigen. The glycans present on rituximab are neutral complex biantennary oligosaccharides with zero, one, and two terminal galactose residues (G0, G1, and G2, respectively). To monitor the variation of the glycosylation during manufacture, the glycans were first enzymatically released from the antibody via digestion with peptide-N-glycosidase F, then derivatized with a charged fluorophore, 8-aminopyrene-1,3,6-trisulfonic acid and further separated by capillary electrophoresis with laser-induced fluorescence detection. All observed glycans were fully resolved, including the positional isomers of G1. The exact nature of the isomers in terms of the location of the terminal galactose was further characterized via multiple enzymatic digestion steps including mannosidase with activity toward specific Man(alpha 1,3) linkage. The optimization and several key parameters, i.e., enzymatic digestion and derivatization, in the assay development will be discussed. Moreover, to ensure that the assay can be used in routine lot release testing, the assay was validated and found to be accurate and precise. The analytical approach described is suitable for characterization as well as routine testing of the N-linked glycan content in any IgG1 monoclonal antibody and glycoproteins in general.

Glycosylation of natural human neutrophil gelatinase B and neutrophil gelatinase B-associated lipocalin

Gelatinase B is a matrix metalloproteinase (MMP-9) involved in tissue remodeling, development, cancer, and inflammation. Neutrophils produce three major forms of (pro)gelatinase B: 92 kDa monomers, homodimers, and complexes of gelatinase B covalently bound to neutrophil gelatinase B-associated lipocalin (NGAL). In contrast to the case for other proteinases, little information about the glycosylation of any natural human MMP is available. Here, both gelatinase B and NGAL were purified from human peripheral blood neutrophils, and the entire contents of the released N- and O-glycan pools were analyzed simultaneously using recently developed high-performance liquid chromatography-based technology. The results are discussed within the context of the domain structure of gelatinase B and a molecular model of NGAL based on data from this study and the three-dimensional nuclear magnetic resonance (NMR) structure of the protein. More than 95% of the N-linked glycans attached to both gelatinase B and NGAL were partially sialylated, core-fucosylated biantennary structures with and without outer arm fucose. The O-linked glycans, which were estimated to comprise approximately 85% of the total sugars on gelatinase B, mainly consisted of type 2 cores with Galbeta1,4GlcNAc (lactosamine) extensions, with or without sialic acid or outer arm fucose. This paper also contains the first report of O-linked glycans attached to NGAL. Although both proteins were isolated from neutrophils and contained O-linked glycans mainly with type 2 cores, the glycans attached to individual serine/threonine residue(s) in NGAL were significantly smaller than those on gelatinase B. In contrast to NGAL, gelatinase B contains a region rich in Ser, Thr, and Pro typical of O-glycosylated mucin-like domains.

Carbohydrate-deficient glycoprotein syndrome type IA (phosphomannomutase-deficiency)

The carbohydrate-deficient glycoprotein or CDG syndromes (OMIM 212065) are a recently delineated group of genetic, multisystem diseases with variable dysmorphic features. The known CDG syndromes are characterized by a partial deficiency of the N-linked glycans of secretory glycoproteins, lysosomal enzymes, and probably also membranous glycoproteins. Due to the deficiency of terminal N-acetylneuraminic acid or sialic acid, the glycan changes can be observed in serum transferrin or other glycoproteins using isoelectrofocusing with immunofixation as the most widely used diagnostic technique. Most patients show a serum sialotransferrin pattern characterized by increased di- and asialotransferrin bands (type I pattern). The majority of patients with type I are phosphomannomutase deficient (type IA), while in a few other patients, deficiencies of phosphomannose isomerase (type IB) or endoplasmic reticulum glucosyltransferase (type IC) have been demonstrated. This review is an update on CDG syndrome type IA.

Structural characterization of the oligosaccharide chains of native and crystallized boar seminal plasma spermadhesin PSP-I and PSP-II glycoforms

The PSP-I/PSP-II heterodimer is the major protein of boar seminal plasma. Both subunits are glycoproteins of the spermadhesin family and each contains a single N-glycosylation site. After enzymatic release of the oligosaccharides from isolated PSP-I and PSP-II, mainly neutral and monosialylated oligosaccharides, and small amounts of disialylated oligosaccharides, were recovered from both proteins. Twenty-two neutral oligosaccharides, 11 monosialylated glycans and three disialylated carbohydrate chains were characterized using mass spectrometric and NMR techniques. PSP-I and PSP-II share the same glycans but differ in their relative molar ratios. Most glycan structures are proximally alpha1-6-fucosylated, diantennary complex-type bearing nonsialylated or alpha2-6-sialylated N-acetyllactosamine or di-N-acetyllactosamine antennae. The majority of nonsialylated N-acetyllactosamine antennae bear terminal alpha1-3-linked Gal residues. In addition, the N-acetylglucosamine residue of nonsialylated N-acetyl and di-N-acetyllactosamine antennae can be modified by an alpha1-3-linked fucose residue. Structures of higher antennarity, as well as structures 3,6-branched at galactose residues, were found in smaller amounts. In one oligosaccharide, N-acetylneuraminic acid is substituted by N-glycolylneuraminic acid. Mass spectrometric analysis of PSP-I and PSP-II glycoforms isolated from crystallized PSP-I/PSP-II heterodimer showed the coexistence of major PSP-I and PSP-II glycoforms in the hexagonal crystals. Oligosaccharides with the NeuNAcalpha2-6GalNAcbeta1-4GlcNAc-R motif block adhesive and activation-related events mediated by CD22, suggesting a possible immunoregulatory activity for PSP-I/PSP-II.

Novel glycosylated forms of human plasma endostatin and circulating endostatin-related fragments of collagen XV

Circulating elongated forms of the angiogenesis inhibitor and potential anti-cancer drug endostatin were isolated from human blood filtrate. Immunoreactive endostatin was identified by a polyclonal rabbit antiserum raised against an N-terminal epitope of the polypeptide and purified by consecutive chromatographic steps and immunoblotting. N- and C-terminal sequence analyses of the isolated molecules revealed different forms of endostatin starting with V(117)HLRPAR. lacking the last and final three residues of the noncollagenous domain 1 (NC-1) of collagen XVIII, respectively. These polypetides are found to be O-glycosylated at T(125) (residue 9) with a glycan structure of the mucin type consisting of galactose N-acetylgalactosamine and N-acetylneuraminic acid residues. Carbohydrate analyses were performed via the semiquantitative HPLC-electrospray ionization mass spectrometry (ESMS) technique after exoglycosidase hydrolysis. Circulating endostatins are present as sialoglycoprotein (22 000 and 21 841 Da +/- 0.02%) and asialoglycoprotein structures (21 710 and 21 549 Da +/- 0.02%), while the two completely deglycosylated forms are obtained only after enzymatic incubation. The described glycosylated endostatins may represent intermediates in the proteolytic pathway of the NC-1 domain of collagen XVIII resulting in bioactive endostatins. Furthermore, immunoreactive endostatin-related C-terminal fragments of human collagen XV are found in the hemofiltrate. These polypeptides exhibit the N-terminal sequences P(66)HLLPPP. and Y(81)EKPALH. of the collagen XV NC-1 domain. ESMS and immunoblotting analyses reveal three glycosylated polypeptides with a molecular mass ranging from 16 to 21 kDa. Due to the high degree of homology between collagen XV and collagen XVIII as well as their analoqous proteolytic processing, functional similarities of collagen XVIII- and XV-related fragments should be revealed in future experiments.

N-linked oligosaccharides can protect target cells from the lysis mediated by NK cells but not by cytotoxic T lymphocytes: role of NKG2-A

We have previously shown that glycophorin A (GPA), inserted by electropulsation into the membrane of K562 cells, protected them from natural killer (NK) cell-mediated cytotoxicity and the unique N-linked oligosaccharide of GPA was essential for resistance to occur. The present study demonstrates that the protection level conferred by GPA is similar to the resistance induced by HLA-Cw3 expressed by transfected K562 cells. A monoclonal antibody against NKG2-A, an NK inhibitory receptor interacting with HLA class I antigens and belonging to the C-type lectin receptor, was able to restore the ability of NK cells to lyse K562 cells expressing HLA-Cw3 at the cell membrane but not electroinserted-GPA, suggesting that the N-linked oligosaccharide of GPA cannot be a ligand for NKG2-A. GPA was then electroinserted into the membrane of two lymphoblastoid B-cell lines: one was sensitive to NK cell-mediated lysis, the other was susceptible to cytotoxic CD8+ T-lymphocyte (CTL)-mediated cytotoxicity. The electroinserted GPA protected the target cells from NK-mediated cytotoxicity, whereas it did not modify the cell susceptibility to lysis by CTL. Endoglycosidase F treatment abolished the resistance towards NK cell-mediated lysis, suggesting that N-linked glycans could inhibit mechanisms used by NK cells to exert their cytotoxic function in agreement with our previous results.

Evolutionary considerations in relating oligosaccharide diversity to biological function

The oligosaccharide chains (glycans) attached to cell surface and extracellular proteins and lipids are known to mediate many important biological roles. However, for many glycans, there are still no evident functions that are of obvious benefit to the organism that synthesizes them. There is also no clear explanation for the extreme complexity and diversity of glycans that can be found on a given glycoconjugate or cell type. Based on the limited information available about the scope and distribution of this diversity among taxonomic groups, it is difficult to see clear trends or patterns consistent with different evolutionary lineages. It appears that closely related species may not necessarily share close similarities in their glycan diversity, and that more derived species may have simpler as well as more complex structures. Intraspecies diversity can also be quite extensive, often without obvious functional relevance. We suggest one general explanation for these observations, that glycan diversification in complex multicellular organisms is driven by evolutionary selection pressures of both endogenous and exogenous origin. We argue that exogenous selection pressures mediated by viral and microbial pathogens and parasites that recognize glycans have played a more prominent role, favoring intra- and interspecies diversity. This also makes it difficult to appreciate and elucidate the specific endogenous roles of the glycans within the organism that synthesizes them.

Isolation and characterisation of the cDNA encoding a glycosylated accessory protein of pea chloroplast DNA polymerase

The cDNA encoding p43, a DNA binding protein from pea chloroplasts (ct) that binds to cognate DNA polymerase and stimulates the polymerase activity, has been cloned and characterised. The characteristic sequence motifs of hydroxyproline-rich glyco-proteins (HRGP) are present in the cDNA corres-ponding to the N-terminal domain of the mature p43. The protein was found to be highly O-arabinosylated. Chemically deglycosylated p43 (i.e. p29) retains its binding to both DNA and pea ct-DNA polymerase but fails to stimulate the DNA polymerase activity. The mature p43 is synthesised as a pre-p43 protein containing a 59 amino acid long transit peptide which undergoes stromal cleavage as evidenced from the post-translational in vitro import of the precursor protein into the isolated intact pea chloroplasts. Surprisingly, p43 is found only in pea chloroplasts. The unique features present in the cloned cDNA indicate that p43 is a novel member of the HRGP family of proteins. Besides p43, no other DNA-polymerase accessory protein with O-glycosylation has been reported yet.

Interaction of Azospirillum lipoferum with wheat germ agglutinin stimulates nitrogen fixation

In vitro, the nitrogen fixation capability of A. lipoferum is efficiently increased in the presence of wheat germ agglutinin (WGA). A putative WGA-binding receptor, a 32-kDa protein, was detected in the cell capsule. The stimulatory effect required N-acetyl-D-glucosamine dimer (GlcNAcdi) terminated sugar side chains of the receptor and was dependent on the number of GlcNAcdi links involved in receptor-WGA interface. Binding to the primary sugar binding sites on WGA had a larger stimulatory effect than binding to the secondary sites. The WGA-receptor complex generated stimulus led to elevated transcription of the nifH and nifA genes and of the glnBA gene cluster but not of the glnA gene from its own promoter. There may well be a signalling cascade contributing to the regulation of nitrogen fixation.

The relevance of N-linked glycosylation to the binding of a ligand to guanylate cyclase C

The role of carbohydrate moieties at the N-linked glycosylation sites of guanylate cyclase C (GC-C), a receptor protein for guanylin, uroguanylin and heat-stable enterotoxin, in ligand binding and structural stability was examined using site-directed mutagenesis of the putative N-linked glycosylation sites in the extracellular domain (ECD) of porcine GC-C. For this purpose, eight mutant proteins of ECD (N9A, N20A, N56A, N172A, N261A, N284A, N334A and N379A) and six mutant proteins of the complete GC-C (N9A, S11A, N172A, T174A, N379A and T381A) were prepared, in which Ala replaced Asn, Ser and Thr at the N-linked glycosylation consensus sites. All the mutant proteins showed a ligand-binding affinity (K(d)) similar to those of the wild-type proteins, although the deletion of a carbohydrate moiety at each of the N-linked glycosylation sites affected the ligand-binding ability of ECD or GC-C to some degree. However, the mutant proteins of ECD (N379A) and GC-C (N379A and T381A) showed considerably decreased binding ability in the context of maximum capacity (B(max)) to a ligand, despite the fact that the expression levels of these mutant proteins were nearly the same as the wild-type proteins. Moreover, the mutant protein of ECD (N379A) was considerably less stable to a denaturant. These results clearly indicate a crucial role for the carbohydrate moiety at N379, which is located near the transmembrane region, in structural stability, the ability to bind to a ligand and the cyclase catalytic activity of GC-C, and provide a route for the elucidation of the mechanism of the interaction between GC-C and a ligand.

Dengue virus type 1 nonstructural glycoprotein NS1 is secreted from mammalian cells as a soluble hexamer in a glycosylation-dependent fashion

Nonstructural glycoprotein NS1, specified by dengue virus type 1 (Den-1), is secreted from infected green monkey kidney (Vero) cells in a major soluble form characterized by biochemical and biophysical means as a unique hexameric species. This noncovalently bound oligomer is formed by three dimeric subunits and has a molecular mass of 310 kDa and a Stokes radius of 64.4 A. During protein export, one of the two oligosaccharides of NS1 is processed into an endo-beta-N-acetylglucosaminidase F-resistant complex-type sugar while the other remains of the polymannose type, protected in the dimeric subunit from the action of maturation enzymes. Complete processing of the complex-type sugar appears to be required for efficient release of soluble NS1 into the culture fluid of infected cells, as suggested by the repressive effects of the N-glycan processing inhibitors swainsonine and deoxymannojyrimicin. These results, together with observations related to the absence of secretion of NS1 from Den-infected insect cells, suggest that maturation and secretion of hexameric NS1 depend on the glycosylation status of the host cell.

Identification and localisation of glycoconjugates in the olfactory mucosa of the armadillo Chaetophractus villosus

Conventional histochemistry and the binding patterns of 22 biotinylated lectins were examined for characterisation of glycoconjugates in the components of the olfactory mucosa of the armadillo Chaetophractus villosus. The mucous lining the olfactory epithelium showed binding sites for DSL, WGA, STL, LEL, PHA-E and JAC. Only the basilar processes of the supporting cells stained for Con-A and S-Con A. The olfactory receptor neurons stained with LEL, LCA, Con A, S-Con A, JAC and PNA. The layer of basal cells did not react with any of the lectins studied. Bowman's glands in the lamina propria showed subpopulations of acinar cells reacting with SBA, S-WGA, WGA, STL, Con A, PSA, PNA, SJA, VVA, JAC and S-Con A, but in our optical studies with lectins we were unable to differentiate between mucous and serous cells in the way that is possible on electron microscopy. The ducts of Bowman's glands were labelled with S-WGA, STL, LEL, PHA-E, BSL-I and JAC. This histochemical study on the glycoconjugates of the olfactory mucosa in the order Xenarthra provides a basis for further experimental investigations.

Oligosaccharides released by hydrazinolysis from Tamm-Horsfall protein of various human donors contain similar high-mannose glycans

As pathophysiological functions claimed for Tamm-Horsfall protein (THP) are related to its sugar moiety, we examined influence of pregnancy and various diseases on high-mannose chains. Hydrazinolysis was used to liberate oligosaccharides from THP polypeptide backbone. After HPLC separation of fluorescently labelled glycans similar profiles of neutral oligosaccharides were observed in THP of healthy subjects, pregnant women, patients with Bartter's syndrome, patients with acute lymphoblastic leukemia and a patient with carbohydrate deficient glycoprotein syndrome. THP contains Man-5, Man-6 and Man-7 glycans, with the preponderant amount of Man-6 glycan (about 7% of total THP oligosaccharides). No statistically significant differences were found in THP high-mannose glycans profiles between control subjects and pregnant women or patients. It is likely that neither pregnancy nor the pathological conditions examined affect high-mannose chains. In our opinion hydrazinolysis as a method of oligosaccharides liberation, in contrast to enzymatic deglycosylation, is more appropriate for analysis of the sugar moiety of THP.

Detection of novel carbohydrate binding activity of interleukin-1

Tamm-Horsfall glycoprotein (THGP) and the oligosaccharide fraction liberated from THGP by hydrazinolysis inhibited tetanus toxoid-induced T cell proliferation. Intact THGP showed approximately 100-fold more inhibitory activity than the free oligosaccharides. After fractionating the oligosaccharides by anion-exchange column chromatography, the inhibitory activity could be detected in a sialidase-resistant acidic oligosaccharide fraction (fraction AR). The inhibitory activity of fraction AR was not observed when the fraction was added to the T cell culture medium 24 h after the addition of tetanus toxoid. Increased concentration of interleukin (IL) 1beta and decreased concentration of IL-2 were observed in the T cell culture medium after the addition of fraction AR. The oligosaccharides in fraction AR also inhibited the growth of an IL-1-dependent cell line, D10-G4. These results strongly suggested that the oligosaccharides in fraction AR bind to IL-1beta and suppress its cytokine activity. IL-1beta actually bound to the fraction AR immobilized on an amino-bonded thin layer plate. Fractionation of the oligosaccharides indicated that only oligosaccharides containing an N-acetylgalactosamine residue and a sulfate residue bound specifically to IL-1beta. Removal of either the sulfate residue or the N-acetylgalactosamine residue from the oligosaccharides abolished both the proliferation-inhibition and IL-1beta binding activities. Since IL-1beta did not bind to thyroid-stimulating hormone, which has the sulfate group at C-4 of the N-acetylgalactosamine residue in its N-linked sugar chains, the binding of IL-1beta toward oligosaccharides in fraction AR was considered to be highly specific.

Bioaffinity based immobilization of enzymes

Procedures that utilize the affinities of biomolecules and ligands for the immobilization of enzymes are gaining increasing acceptance in the construction of sensitive enzyme-based analytical devices as well as for other applications. The strong affinity of polyclonal/monoclonal antibodies for specific enzymes and those of lectins for glycoenzymes bearing appropriate oligosaccharides have been generally employed for the purpose. Potential of affinity pairs like cellulose-cellulose binding domain bearing enzymes and immobilized metal ionsurface histidine bearing enzymes has also been recognised. The bioaffinity based immobilization procedures usually yield preparations exhibiting high catalytic activity and improved stability against denaturation. Bioaffinity based immobilizations are usually reversible facilitating the reuse of support matrix, orient the enzymes favourably and offer the possibility of enzyme immobilization directly from partially pure enzyme preparations or even cell lysates. Enzyme lacking innate ability to bind to various affinity supports can be made to bind to them by chemically or genetically linking the enzymes with appropriate polypeptides/domains like the cellulose binding domain, protein A, histidine-rich peptides, single chain antibodies, etc.

Genetic engineering of recombinant glycoproteins and the glycosylation pathway in mammalian host cells

The analysis of many natural glycoproteins and their recombinant counterparts from mammalian hosts has revealed that the basic oligosaccharide structures and the site occupancy of glycosylated polypeptides are primarily dictated by the protein conformation. The equipment of many frequently used host cells (e.g. BHK-21 and CHO-cells) with glycosyltransferases, nucleotide-sugar synthases and transporters appears to be sufficient to guarantee complex-type glycosylation of recombinant proteins with a high degree of terminal alpha2-3 sialylation even under high expression conditions. Some human tissue-specific terminal carbohydrate motifs are not synthesized by these cells since they lack the proper sugar-transferring enzymes (e.g. alpha1-3/4 fucosyltransferases, alpha2-6 sialyltransferases). Glycosylation engineering of these hosts by stable transfection with genes encoding terminal human glycosyltransferases allows to obtain products with tailored (human tissue-specific) glycosylation in high yields. Using site-directed mutagenesis, unglycosylated polypeptides can be successfully converted in N- and/or O-glycoproteins by transferring glycosylation domains (consisting of 7-17 amino acids) from donor glycoproteins to different loop regions of acceptor proteins. The genetic engineering of glycoproteins and of host cell lines are considered to provide a versatile tool to obtain therapeutic glyco-products with novel/improved in-vivo properties, e.g. by introduction of specific tissue-targeting signals by a rational design of terminal glycosylation motifs.

Structural analysis of glycoconjugates by on-target enzymatic digestion and MALDI-TOF-MS

Exoglycosidase digestion combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has been demonstrated to be an effective method for the structural characterization of glycoconjugates and oligosaccharides in picomolar amounts. A sample preparation method is described, in which 6-aza-2-thiothymine (ATT) in water is used as matrix and enzymes are dialyzed before use against a low concentration of volatile buffer such as ammonium acetate. Under these conditions, a series of sequential on-target exoglycosidase treatments was carried out in one single analyte spot in the presence of ATT matrix. Subsequent mass spectrometric analysis of the resulting products yielded information on both the completeness of the reaction and structural features of the glycoconjugates such as monosaccharide sequence, branching pattern, and anomeric configurations of the corresponding glycosidic linkages. The results show that all exoglycosidases used retain their activity in the presence of ATT matrix. Hence, structural analysis of carbohydrates or mixtures thereof can be performed very fast, without intermediate desalting steps or sample splitting. This approach is illustrated by the analysis of underivatized glycans, oligosaccharide derivatives, glycopeptides, and glycolipids. Depending on the analyte, amounts of sample required could be limited to a few picomoles.

Carbohydrate-deficient glycoprotein syndromes: inborn errors of protein glycosylation

The carbohydrate-deficient glycoprotein (CDG) syndromes (CDGS) are a series of autosomal recessive enzyme deficiencies which result in incomplete glycosylation of plasma proteins. CDGS types Ia and Ib have been related to deficiencies of phosphomannomutase and phosphomannose isomerase, respectively, while CDGS type II results from a deficiency of N-acetylglucosaminyltransferase II. Secondary CDG syndromes are associated with galactosaemia and hereditary fructose intolerance. The diagnosis of CDGS is most easily made by studying the glycoforms of suitable marker proteins using either electrophoresis or isoelectric focusing. This paper reviews the structure of the glycan chains of proteins and structural alterations in CDGS. It also outlines analytical techniques which are useful in the laboratory study of protein glycoforms and the diagnosis of CDGS.

Expression patterns of complex glycoconjugates and endogenous lectins during fetal development of the viscerocranium

Experimental evidence suggests that carbohydrates and their corresponding receptors (endogenous lectins) decode biological information. Therefore, the expression of complex oligosaccharides--the potential ligand part of this recognition system--during chondrogenesis and osteogenesis was determined in the viscerocranium of fetal rats by mapping the staining patterns of exogenous lectins. Results were compared with the expression of bone- and/or cartilage-specific core proteins and the binding profiles of neoglycoconjugates. These synthetic tools make possible the localization of sugar-ligand-binding sites. The spatial and temporal distribution patterns of glycoconjugates were highly dynamic and demonstrated a clear correlation with characteristic morphological modifications. The glycobiological characterization of precartilage mesenchymal cells revealed distinct differences compared to prospective bone anlagen. Especially the binding of the exogenous lectin from Griffonia simplicifolia II, that selectively visualized prechondral aggregations, reveals that regulation of early chondral growth is at least phenomenologically correlated with a relatively atypical oligosaccharide composition terminating with N-acetylglucosamine.

Anti-GM3 antibodies activate calcium inflow and inhibit platelet-derived growth factor beta receptors (PDGFbetar) in T51B rat liver epithelial cells

Glycolipids expressed in the plasma membrane regulate a variety of cellular processes including intracellular calcium dynamics. We used flow cytometry to characterize the glycoconjugates on the plasma membrane of T51B liver epithelial cells. Antibodies against glycolipids found to be present were tested for their ability elevate intracellular calcium. An antibody against GM3 (DH2) nearly doubles intracellular calcium while an antibody against type II chains (1B2) increases calcium to nearly four times the baseline level, similar to levels obtained with epidermal growth factor (EGF). The antibodies stimulated calcium inflow but did not trigger calcium release from internal stores. In addition DH2 but not 1B2 inhibited platelet-derived growth factor beta receptor (PDGFbetar) function. This is the first demonstration of activation of calcium inflow by agents that bind GM3 and type II chains. The ganglioside-mediated calcium inflow is likely to stimulate secretion by these liver cells.

Oligosaccharides of recombinant mouse gelatinase B variants

Gelatinase B (matrix metalloproteinase-9, MMP-9) contains three N-glycosylation sites and a Ser/Thr/Pro-rich type V collagen domain with repetitive attachment sites for O-linked sugars. Recombinant mouse gelatinase B was expressed in the yeast Pichia pastoris and the N-linked oligosaccharides of the truncated glycoprotein variants were analysed by in gel enzymatic release followed by mass spectrometry and normal phase HPLC. This technology, despite of the limiting amount of material, allowed the analysis of the formula of N- and O-linked sugars of the different glycoprotein variants. The 112/99- and 88-kDa gelatinase B forms each contained an oligomannose series (Man8GlcNAc2 to Man15GlcNAc2). Analysis of the hydrazine-released sugars showed that the O-linked oligosaccharides contained alpha1-2, alpha1-3 or alpha1-6 linked mannoses. These results were confirmed by lectin blot analysis of intact and glycosidase-treated enzyme variants.

Disaccharides permeases: constituents of xylanolytic and mannanolytic systems of Aureobasidium pullulans

Aureobasidium pullulans, a yeast-like microorganism was found to produce mannobiose permease and xylobiose permease, transporting beta-1,4-mannobiose or beta-1,4-xylobiose into the cells from extracellular media. Both permeases are induced by the same inducers as the corresponding hemicellulolytic enzyme systems. Mannobiose permease is induced by beta-1,4-mannobiose or is formed in the cells growing on mannan (inducers of beta-mannanolytic enzymes) and xylobiose permease is induced by d-xylose, beta-1,4-xylobiose or during the growth on xylan (inducers of xylanolytic enzymes). The permeases are energy dependent, synthesized de novo and their activities are inhibited by d-glucose. Since mannobiose permease transports beta-1,4-mannobiose, xylobiose permease appears to be less specific and transports beta-1,4-mannobiose, beta-1,4-xylobiose and methyl beta-d-xylopyranoside. Methyl beta-d-mannopyranoside or methyl beta-d-xylopyranoside serve as less efficient inducers of the corresponding permeases than beta-1,4-mannobiose or beta-1, 4-xylobiose.

Detection of O-mannosyl glycans in rabbit skeletal muscle alpha-dystroglycan

alpha-Dystroglycan, which is a cell surface component of dystroglycan complex, is known to bind laminin in basal lamina of muscle cells and Schwann cells. We found previously that a novel O-glycan, Siaalpha2-3Galbeta1-4GlcNAcbeta1-2Man, is the major oligosaccharide in bovine peripheral nerve alpha-dystroglycan, and that this structure might mediate the binding of laminin. In order to determine whether this structure is specific for peripheral nerve alpha-dystroglycan or present on different forms of alpha-dystroglycan, we analyzed the structures of the sialylated O-glycans of rabbit skeletal muscle alpha-dystroglycan. Their structures were elucidated to be a mixture of a core 1 O-glycan and the same O-mannosyl glycan that we found in bovine peripheral nerve. These results indicate that alpha-dystroglycan in different species and tissues share a common structure of its major O-linked acidic carbohydrate, suggesting its relevance to the basic functional role of alpha-dystroglycan.

The mannose 6-phosphate/insulin-like growth factor II receptor is a nanomolar affinity receptor for glycosylated human leukemia inhibitory factor

Comparison of the binding properties of non-glycosylated, glycosylated human leukemia inhibitory factor (LIF) and monoclonal antibodies (mAbs) directed at gp190/LIF-receptor beta subunit showed that most of the low affinity (nanomolar) receptors expressed by a variety of cell lines are not due to gp190. These receptors bind glycosylated LIF produced in Chinese hamster ovary cells (CHO LIF) (Kd = 6.9 nM) but not Escherichia coli-derived LIF or CHO LIF treated with endoglycosidase F. CHO LIF binding to these receptors is neither affected by anti-gp190 mAbs nor by anti-gp130 mAbs and is specifically inhibited by low concentrations of mannose 6-phosphate (Man-6-P) (IC50 = 40 microM), suggesting that they could be related to Man-6-P receptors. The identity of this LIF binding component with the Man-6-P/insulin-like growth factor-II receptor (Man-6-P/IGFII-R) was supported by several findings. (i) It has a molecular mass very similar to that of the Man-6-P/IGFII-R (270 kDa); (ii) the complex of LIF cross-linked to this receptor is immunoprecipitated by a polyclonal anti-Man-6-P/IGFII-R antibody; (iii) this antibody inhibits LIF and IGFII binding to the receptor with comparable efficiencies; (iv) soluble Man-6-P/IGFII-R purified from serum binds glycosylated LIF (Kd = 4.3 nM) but not E. coli LIF. The potential role of Man-6-P/IGFII-R in LIF processing and biological activity is discussed.