Comprehensive serum N-glycan profiling identifies a biomarker panel for early diagnosis of non-small-cell lung cancer

Aberrant serum N-glycan profiles have been observed in multiple cancers including non-small-cell lung cancer (NSCLC), yet the potential of N-glycans in the early diagnosis of NSCLC remains to be determined. In this study, serum N-glycan profiles of 275 NSCLC patients and 309 healthy controls were characterized by MALDI-TOF-MS. The levels of serum N-glycans and N-glycosylation patterns were compared between NSCLC and control groups. In addition, a panel of N-glycan biomarkers for NSCLC diagnosis was established and validated using machine learning algorithms. As a result, a total of 54 N-glycan structures were identified in human serum. Compared with healthy controls, 29 serum N-glycans were increased or decreased in NSCLC patients. N-glycan abundance in different histological types or clinical stages of NSCLC presented differentiated changes. Furthermore, an optimal biomarker panel of eight N-glycans was constructed based on logistic regression, with an AUC of 0.86 in the validation set. Notably, this model also showed a desirable capacity in distinguishing early-stage patients from healthy controls (AUC = 0.88). In conclusion, our work highlights the abnormal N-glycan profiles in NSCLC and provides supports potential application of N-glycan biomarker panel in clinical NSCLC detection.     

The bisecting GlcNAc in cell growth control and tumor progression

The bisecting GlcNAc is transferred to the core mannose residue of complex or hybrid N-glycans on glycoproteins by the β1,4-N-acetylglucosaminyltransferase III (GlcNAcT-III) or MGAT3. The addition of the bisecting GlcNAc confers unique lectin recognition properties to N-glycans. Thus, LEC10 gain-of-function Chinese hamster ovary (CHO) cells selected for the acquisition of ricin resistance, carry N-glycans with a bisecting GlcNAc, which enhances the binding of the erythroagglutinin E-PHA, but reduces the binding of ricin and galectins-1, -3 and -8. The altered interaction with galactose-binding lectins suggests that the bisecting GlcNAc affects N-glycan conformation. LEC10 mutants expressing polyoma middle T antigen (PyMT) exhibit reduced growth factor signaling. Furthermore, PyMT-induced mammary tumors lacking MGAT3, progress more rapidly than tumors with the bisecting GlcNAc on N-glycans of cell surface glycoproteins. In recent years, evidence for a new paradigm of cell growth control has emerged involving regulation of cell surface residency of growth factor and cytokine receptors via interactions and cross-linking of their branched N-glycans with a lattice of galectin(s). Specific cross-linking of glycoprotein receptors in the lattice regulates their endocytosis, leading to effects on growth factor-induced signaling. This review will describe evidence that the bisecting GlcNAc of N-glycans regulates cellular signaling and tumor progression, apparently through modulating N-glycan/galectin interactions.     

Serum DSG2 as a potential biomarker for diagnosis of esophageal squamous cell carcinoma and esophagogastric junction adenocarcinoma

Background: Exploration of serum biomarkers for early detection of upper gastrointestinal cancer is required. Here, we aimed to evaluate the diagnostic potential of serum desmoglein-2 (DSG2) in patients with esophageal squamous cell carcinoma (ESCC) and esophagogastric junction adenocarcinoma (EJA).Methods: Serum DSG2 levels were measured by enzyme-linked immunosorbent assay (ELISA) in 459 participants including 151 patients with ESCC, 96 with EJA, and 212 healthy controls. Receiver operating characteristic (ROC) curves were used to evaluate diagnostic accuracy.Results: Levels of serum DSG2 were significantly higher in patients with ESCC and EJA than those in healthy controls (P<0.001). Detection of serum DSG2 demonstrated an area under the ROC curve (AUC) value of 0.724, sensitivity of 38.1%, and specificity of 84.8% for the diagnosis of ESCC in the training cohort, and AUC 0.736, sensitivity 58.2%, and specificity 84.7% in the validation cohort. For diagnosis of EJA, measurement of DSG2 provided a sensitivity of 29.2%, a specificity of 90.2%, and AUC of 0.698. Similar results were observed for the diagnosis of early-stage ESCC (AUC 0.715 and 0.722, sensitivity 36.3 and 50%, and specificity 84.8 and 84.7%, for training and validation cohorts, respectively) and early-stage EJA (AUC 0.704, sensitivity 44.4%, and specificity 86.9%). Analysis of clinical data indicated that DSG2 levels were significantly associated with patient age and histological grade in ESCC (P<0.05).Conclusion: Serum DSG2 may be a diagnostic biomarker for ESCC and EJA.     

Substitutions in the N-glycan core as regulators of biorecognition: the case of core-fucose and bisecting GlcNAc moieties

Core fucosylation and the bisecting N-acetylglucosamine residue are prominent natural substitutions of the N-glycan core. To address the issue of whether these two substituents can modulate ligand properties of complex-type biantennary N-glycans, we performed chemoenzymatic synthesis of the respective galactosylated and alpha2,3/6-sialylated N-glycans. Neoglycoproteins were then produced to determine these glycans' reactivities with sugar receptors in solid-phase assays and with tumor cells in vitro as well as their in vivo biodistribution profiles in mice. Slight protein-type-dependent changes were noted in lectin binding, including adhesion/growth-regulatory galectins as study objects, when the data were related to properties of N-glycans without or with only one core substituent. Monitoring binding in vitro revealed cell-type-dependent changes. They delimited the ligand activity of this glycan type from that of chains with un- and monosubstituted cores. A markedly prolonged serum half-life was conferred to the neoglycoprotein by the galactose-terminated N-glycan, which together with increased organ retention of all three neoglycoproteins underscores the conspicuous relevance for glycoengineering of pharmaproteins. The predominant presentation of the two branches in the disubstituted N-glycan as extended (alpha1,3-antenna) and backfolded (alpha1,6-antenna) forms, revealed by molecular dynamics simulations, can underlie the measured characteristics. These results obtained by a combined strategy further support the concept of viewing N-glycan core substitutions as non-random additions which exert a modulatory role on ligand properties. Moreover, our data inspire us to devise new, non-natural modifications to realize the full potential of glycoengineering for diagnostic and therapeutic purposes.     

N-glycans in liver-secreted and immunoglogulin-derived protein fractions

N-glycosylation of proteins provides a rich source of information on liver disease progression because majority of serum glycoproteins, with the exception of immunoglobulins, are secreted by the liver. In this report, we present results of an optimized workflow for MALDI-TOF analysis of permethylated N-glycans detached from serum proteins and separated into liver secreted and immunoglobulin fractions. We have compared relative intensities of N-glycans in 23 healthy controls and 23 cirrhosis patients. We were able to detect 82 N-glycans associated primarily with liver secreted glycoproteins, 54 N-glycans in the protein G bound fraction and 52 N-glycans in the fraction bound to protein A. The N-glycan composition of the fractions differed substantially, independent of liver disease. The relative abundance of approximately 53% N-glycans in all fractions was significantly altered in the cirrhotic liver. The removal of immunoglobulins allowed detection of an increase in a series of high mannose and hybrid N-glycans associated with the liver secreted protein fraction.     

beta1,4-N-Acetylglucosaminyltransferase III potentiates beta1 integrin-mediated neuritogenesis induced by serum deprivation in Neuro2a cells

Aspects of the biological significance of the bisecting N-acetylglucosamine (GlcNAc) structure on N-glycans introduced by beta1,4-N-acetylglucosaminyltransferase III (GnT-III) in Neuro2a cell differentiation are demonstrated. The overexpression of GnT-III in the cells led to the induction of axon-like processes with numerous neurites and swellings, in which beta1 integrin was localized, under conditions of serum starvation. This enhancement in neuritogenesis was suppressed by either the addition of a bisecting GlcNAc-containing N-glycan or erythroagglutinating phytohemagglutinin (E(4)-PHA), which preferentially recognizes the bisecting GlcNAc. GnT-III-promoted neuritogenesis was also significantly perturbed by treatment with a functional blocking anti-beta1 integrin antibody. In fact, beta1 integrin was found to be one of the target proteins of GnT-III, as confirmed by a pull-down assay with E(4)-PHA. These data suggest that N-glycans with a bisecting GlcNAc on target molecules, such as beta1 integrin, play important roles in the regulation of neuritogenesis.     

Analysis of N-glycan in serum glycoproteins from db/db mice and humans with type 2 diabetes

Glycosylation has an important role in regulating properties of proteins and is associated with many diseases. To examine the alteration of serum N-glycans in type 2 diabetes, we used the db/db mouse model. Serum N-glycans were fluorescence labeled and applied to HPLC. There were reproducible differences in N-glycan profiles between the db/db mouse model and the db/+ control. The structures of the oligosaccharides, which had changed in their amounts, were analyzed by a two-dimensional mapping method, matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, and exoglycosidase digestion. Those analyses revealed an increase in the N-glycans possessing alpha1,6-fucose in the serum of db/db mice. The level of alpha1,6-fucosyltransferase mRNA was increased in the liver of the db/db mice. The ratio of a biantennary N-glycan with alpha1,6-fucose to that without alpha1,6-fucose in the liver tissue of the db/db mouse was increased relative to the db/+ control. Next, we analyzed the serum N-glycan profile in human subjects with type 2 diabetes and found an increased amount of a biantennary N-glycan that had an alpha1,6-fucose with a bisecting N-acetylglucosamine. In conclusion, the increase in alpha1,6-fucosylation is a striking change in the serum N-glycans of the db/db mice, whereas the change in the fucosylation in humans with type 2 diabetes was small, albeit statistically significant. It is likely that the change is caused, at least partially, by the increase in the alpha1,6-fucosyltransferase mRNA level in the liver. The increased alpha1,6-fucosylation may affect protein properties associated with the pathophysiology of type 2 diabetes.     

Evidence for a site-specific fucosylation of N-linked oligosaccharide of immunoglobulin A1 from normal human serum

Glycopeptides containing the N-linked oligosaccharide from human serum IgA1 were analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS). Two glycopeptides, GP1 and GP2, prepared from the endoproteinase Asp-N digest of the IgA1 heavy chain, were derived from the CH2 domain (N-glycan site at Asn263) and the tailpiece portion (N-glycan site at Asn459), respectively. The structure of the attached sugar chain was deduced from the mass number of the glycopeptide and confirmed by a two-dimensional mapping technique for a pyridylaminated oligosaccharide. GP1 was composed of two major components having a fully galactosylated bianntena sugar chain with or without a bisecting N-acetylglucosamine (GlcNAc) residue. On the other hand, the GP2 fraction corresponded to the glycopeptides having a fully galactosylated and fucosylated bianntena sugar chain partly bearing a bisecting GlcNAc residue. Thus, the site-specific fucosylation of the N-linked oligosaccharide on the tailpiece of the 1 chain became evident for normal human serum IgA1.     

Analysis of IgA1 N-glycosylation and its contribution to FcalphaRI binding

The IgA isotype of human antibodies triggers inflammatory responses via the IgA-specific receptor FcalphaRI (CD89). Structural studies have suggested that IgA1 N-glycans could modulate the interaction with FcalphaRI. We have carried out detailed biophysical analyses of three IgA1 samples purified from human serum and recombinant IgA1-Fc and compared their binding to FcalphaRI. Analytical ultracentrifugation revealed wide variation in the distribution of polymeric species between IgA1 samples, and Fourier transform ion cyclotron resonance mass spectrometry showed overlapping but distinct populations of N-glycan species between IgA1 samples. Kinetic and equilibrium data from surface plasmon resonance experiments revealed that variation in the IgA1 C H2 N-glycans had no effect on the kinetics or affinity constants for binding to FcalphaRI. Indeed, complete enzymatic removal of the IgA1 N-glycans yielded superimposable binding curves. These findings have implications for renal diseases such as IgA nephropathy.     

Serum proteomic profiling for the early diagnosis of colorectal cancer

No ideal serum biomarker currently exists for the early diagnosis of colorectal cancer (CRC). Magnetic bead‐based fractionation coupled with MALDI‐TOF MS was used to screen serum samples from CRC patients, healthy controls, and other cancer patients. A diagnostic model with five proteomic features (m/z 1778.97, 1866.16, 1934.65, 2022.46, and 4588.53) was generated using Fisher algorithm with best performance. The Fisher‐based model could discriminate CRC patients from the controls with 100% (46/46) sensitivity and 100% (35/35) specificity in the training set, 95.6% (43/45) sensitivity and 83.3% (35/42) specificity in the test set. We further validated the model with 94.4% (254/269) sensitivity and 75.5% (83/110) specificity in the external independent group. In other cancers group, the Fisher‐based model classified 25 of 46 samples (54.3%) as positive and the other 21 as negative. With FT‐ICR‐MS, the proteomic features of m/z 1778.97, 1866.16, 1934.65, and 2022.46, of which intensities decreased significantly in CRC, were identified as fragments of complement C3f. Therefore, the Fisher‐based model containing five proteomic features was able to effectively differentiate CRC patients from healthy controls and other cancers with a high sensitivity and specificity, and may be CRC‐specific. Serum complement C3f, which was significantly decreased in CRC group, may be relevant to the incidence of CRC. J. Cell. Biochem. 114: 448–455, 2013. © 2012 Wiley Periodicals, Inc.     

CSF N-Glycan Profiles to Investigate Biomarkers in Brain Developmental Disorders: Application to Leukodystrophies Related to eIF2B Mutations

Background

Primary or secondary abnormalities of glycosylation have been reported in various brain diseases. Decreased asialotransferrin to sialotransferrin ratio in cerebrospinal fluid (CSF) is a diagnostic marker of leukodystrophies related to mutations of genes encoding translation initiation factor, EIF2B. We investigated the CSF glycome of eIF2B-mutated patients and age-matched normal individuals in order to further characterize the glycosylation defect for possible use as a biomarker.

Methodology/Principal Findings

We conducted a differential N-glycan analysis using MALDI-TOF/MS of permethylated N-glycans in CSF and plasma of controls and eIF2B-mutated patients. We found in control CSF that tri-antennary/bisecting and high mannose structures were highly represented in samples obtained between 1 to 5 years of age, whereas fucosylated, sialylated structures were predominant at later age. In CSF, but not in plasma, of eIF2B-mutated patient samples, we found increased relative intensity of bi-antennary structures and decreased tri-antennary/bisecting structures in N-glycan profiles. Four of these structures appeared to be biomarker candidates of glycomic profiles of eIF2B-related disorders.

Conclusion

Our results suggest a dynamic development of normal CSF N-glycan profiles from high mannose type structures to complex sialylated structures that could be correlated with postnatal brain maturation. CSF N-glycome analysis shows relevant quantitative changes associated with eIF2B related disorders. This approach could be applied to other neurological disorders involving developmental gliogenesis/synaptogenesis abnormalities.     

Serum miR-518e-5p is a potential biomarker for secondary imatinib-resistant gastrointestinal stromal tumor

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumor of the intestinal tract. Imatinib is used as first-line therapy for GIST patients; however, secondary imatinib resistance poses a significant clinical challenge. Here, we analyzed serum miRNA expression profiles to identify specific serum miRNAs that could be used as early diagnostic markers. Candidate miRNAs were validated using Taqman quantitative PCR with serum samples from secondary imatinib-resistant GIST patients (n?=?39), imatinib-sensitive GIST patients (n?=?37), and healthy controls (n?=?28). Serum miR-518e-5p and miR-548e levels were higher in secondary imatinib-resistant GIST than imatinib-sensitive GIST patients or healthy controls (P?<?0.0001). However, ROC analysis indicated that only miR-518e-5p could distinguish imatinib-resistant GIST. To discriminate imatinib-resistant from imatinib-sensitive GIST patients, the AUC for serum miR-518e-5p was 0.9938, with 99.8% sensitivity and 82.1% specificity. Serum miR-518e-5p could also discriminate imatinib-resistant GIST patients from healthy controls with 99.9% sensitivity and 97.4% specificity. These data indicate that serum miR-518e-5p is a potentially promising non-invasive biomarker for early detection and diagnosis of secondary imatinib-resistant GIST.     

A specific serum IgA antibody discriminates pneumonia from colonization state in patients with Pseudomonas aeruginosa in sputum culture

We attempted to develop a new specific antibody detection method for discriminating infection state from colonization state in hospitalized immunocompromised patients with a positive sputum culture for Pseudomonas aeruginosa. Serum samples from 65 patients with P. aeruginosa in sputum culture (total PA patients), including 24 patients with P. aeruginosa-related pulmonary infections (PA infection group) and 21 patients without pulmonary infections (PA colonization group), as well as samples from 20 patients positive for other bacteria in blood culture (non-PA infection group) and 38 healthy controls were examined and compared for IgG and IgA anti-P. aeruginosa antibodies by a newly developed enzyme-linked immunosorbent assay (ELISA). Both IgG and IgA antibody ELISA showed satisfactory reproducibility with low coefficient of variation (CV) percent, and western blotting analysis showed two protein bands as the corresponding antigens common to both antibodies. The serum levels of both antibodies in all the PA patients were higher than those in the healthy controls with high significance (p < 0.0001). The PA infection group showed significantly higher mean levels of both IgG and IgA class antibodies than the PA colonization group, non-PA infection group and healthy controls (each, p < 0.0001). In receiver operating characteristic (ROC) curves analysis to differentiate between total PA infections and the PA colonization group, the area under curve (AUC) of the IgA antibody (0.848) was significantly larger than the AUC of the IgG antibody (0.677) (p = 0.019). At the optimal IgA antibody cutoff value for differentiation of 1.37 units/mL, the sensitivity and specificity of IgA anti-P. aeruginosa ELISA were 83.3% and 85.7%, respectively. These findings suggest that IgA antibody ELISA, rather than IgG antibody ELISA, may be useful for differentiating P. aeruginosa-related pneumonia from latent colonization in immunocompromised patients with a positive sputum culture.     

腺苷脱氨酶及同工酶对自身免疫病诊断和病情监测的作用

摘要 目的：检测腺苷脱氨酶(ADA)及其同工酶在自身免疫病患者血清中的变化,探讨其诊断和病情监测作用。方法：收集70例系统性红斑狼疮（SLE）、114例类风湿性关节炎(RA)、55例强直性脊柱炎(AS)、及其年龄性别对应的健康血清标本。测定血清总ADA（tADA）、ADA1及ADA2活性。ROC曲线分析其诊断价值。结果：与健康对照相比,ADA活性在SLE患者血清中显著升高[tADA：15（12,20）vs 8（7,10）U/L;ADA1：3.5（2,5）vs 3（2,3）U/L;ADA2：11（8,15）vs 6（5,7）U/L;P<0.01）]。与健康对照相比,RA患者血清中tADA和ADA1活性无显著变化(P>0.05),ADA2活性水平升高[8（5.25,10）vs 7（5,9）U/L,P<0.05）];与健康对照相比,AS患者血清中tADA和ADA1活性无显著变化(P>0.05),ADA2活性升高[7（5,9）vs 6（5,7）U/L,P<0.05）]。ROC分析显示tADA及ADA2对SLE具有较好诊断价值（tADA：88.6%特异性、77.1%敏感性;ADA2：92.9%特异性、68.6%敏感性）。ADA活性对RA及AS患者无诊断价值。spearman相关性分析显示,tADA活性与SLE患者疾病活动度有一定正相关性（r=0.303,P=0.011)。结论：血清tADA活性检测可作为SLE辅助诊断和病情监测指标。     

N-glycans of SREC-I (scavenger receptor expressed by endothelial cells): essential role for ligand binding, trafficking and stability

Scavenger receptor expressed by endothelial cells (SREC-I) mediates the endocytosis of chemically modified lipoproteins such as acetylated low-density lipoprotein (Ac-LDL) and oxidized LDL and is implicated in atherogenesis. We produced recombinant SREC-I in Chinese hamster ovary-K1 cells and identified three potential glycosylation sites, Asn(289), Asn(382) and Asn(393), which were all glycosylated. To determine the function of N-glycans in SREC-I, we characterized SREC-I mutant proteins by intracellular distribution and the cellular incorporation rate of Ac-LDL. N382Q/N393Q and N289Q/N382Q/N393Q were sequestered in the endoplasmic reticulum, resulting in a severe reduction in the cellular incorporation of Ac-LDL. N382Q showed a normal cell surface residency and an enhanced affinity for Ac-LDL, resulting in an elevated Ac-LDL cellular incorporation. These results indicate that the N-glycan of Asn(393) regulates the intracellular sorting of SREC-I and that the N-glycan of Asn(382) controls ligand-binding affinity. Furthermore, we detected an enhanced trypsin sensitivity of the N289Q. Glycan structure analyses revealed that the core-fucosylated bi-antennary is the common major structure at all glycosylation sites. In addition, tri- and tetra-antennary were detected as minor constituents at Asn(289). A bisecting GlcNAc was also detected at Asn(382) and Asn(393). Structural analyses and homology modeling of SREC-I suggest that the N-glycan bearing a β1-6GlcNAc branch at Asn(289) protects from proteinase attack and thus confers a higher stability on SREC-I. These data indicate that Asn(289)-, Asn(382)- and Asn(393)-linked N-glycans of SREC-I have distinct functions in regulating proteolytic resistance, ligand-binding affinity and subcellular localization, all of which might be involved in the development of atherogenesis.     

Serum miR-1297: a promising diagnostic biomarker in esophageal squamous cell carcinoma

We aimed to value the diagnostic potential of serum miR-1297 in esophageal squamous cell cancer (ESCC). Its expression level was detected in 156 pairs of patients with ESCC and healthy volunteers using quantitative real-time polymerase chain reaction (qRT-PCR) method. It was statistically decreased in ESCC patients compared with healthy controls. AUC based on serum miR-1297 was 0.840?±?0.035 in discovery group and 0.837?±?0.034 in validation group. Further analysis on early-stage patients revealed that the AUC was 0.819?±?0.053 in discovery group and 0.814?±?0.044 in validation group. Its sensitivity and specificity were promising. In conclusion, serum miR-1297 can serve as an ideal indicator for the diagnosis of ESCC.     

心肺运动试验用于冠心病诊断价值的临床研究*

目的: 评估心肺运动试验（CPET）相关指标对于冠心病的诊断价值。方法: 选择156例疑诊为冠心病的患者（病情相对稳定,年龄在18~80岁）行CPET、运动负荷心电图及冠状动脉造影,以冠状动脉造影结果为标准,分析CPET相关指标（峰值摄氧量％预计值Peak VO₂%pred、峰值氧脉搏％预计值Peak O₂ pulse%pred、摄氧量对应功率的做功效率（ΔVO₂/ΔWR）诊断冠心病的敏感度、特异度及其诊断价值。结果: Peak VO₂%pred的最佳截断点是≤69%pred,其诊断冠心病的敏感度为55.1%,特异度为77.0%,AUC为0.698。Peak O₂ pulse%pred最佳截断点诊断冠心病的敏感度为50.7%,特异度为72.4%,AUC为 0.58。ΔVO₂/ΔWR最佳截断点处其诊断冠心病的敏感度为44.9%,特异度为87.4%,AUC为0.647。Peak VO₂%pred及ΔVO₂/ΔWR敏感度远高于负荷心电图,差异有统计学意义（P<0.01）。结论: CPET部分指标诊断冠心病的敏感度优于运动负荷心电图,最佳截断点处特异度及诊断价值均较高,而且CPET本身也包括连续动态全程心电图分析,不建议各自分割使用,主张所有指标整体整合分析使用。CPET相关指标对冠心病诊断有预测价值,可以早期、较准确的诊断冠心病。     

Crocus sativus lectin recognizes Man3GlcNAc in the N-glycan core structure

Crocus sativus lectin (CSL) is one of the truly mannose-specific plant lectins that has a unique binding specificity that sets it apart from others. We studied sugar-binding specificity of CSL in detail by a solution phase method (fluorescence polarization) and three solid phase methods (flow injection, surface plasmon resonance, and microtiter plate), using a number of different glycopeptides and oligosaccharides. CSL binds the branched mannotriose structure in the N-glycan core. Substitution of the terminal Man in the Manalpha(1-3)Man branch with GlcNAc drastically decreases binding affinity much more than masking of the terminal Man in the Manalpha(1-6)Man branch. Most interestingly, the beta-Man-linked GlcNAc in N-glycan core structure contributes greatly to the binding. The effect of this GlcNAc is so strong that it can substantially offset the negative effect of substitution on the nonreducing terminal Man residues. On the other hand, the GlcNAc that is usually attached to Asn in N-glycans and the l-Fuc linked at the 6-position of the GlcNAc are irrelevant to the binding. A bisecting GlcNAc neither contributes to nor interferes with the binding. This unique binding specificity of CSL offers many possibilities of its use in analytical and preparative applications.     

N-glycan structures from the major glycoproteins of pigeon egg white: predominance of terminal Galalpha(1)Gal

N-Glycans from major glycoproteins of pigeon egg white (ovotransferrin, ovomucoid, and ovalbumins) were enzymatically released and were reductively aminated with 2-aminopyridine, separated, and structurally characterized by mass spectrometry and a three-dimensional mapping technique using three different columns of high performance liquid chromatography (HPLC) (Takahashi, N., Nakagawa, H., Fujikawa, K., Kawamura, Y., and Tomiya, N. (1995) Anal. Biochem. 226, 139-146). Twenty-five major N-glycan structures, all of them hitherto unknown, were identified as pyridylamino derivatives. Of these, 13 were neutral, 10 were monosialyl, and 2 were disialyl oligosaccharides. All N-glycans contain from one to four Galalpha(1,4)Galbeta(1,4) sequences at the nonreducing terminal positions and are devoid of fucose residues. N-Acetylneuraminic acids were alpha(2,6)-linked only to beta-galactose. The HPLC profiles of the N-glycans from four different glycoproteins were qualitatively very similar to each other, but not identical in the peak distributions. Monosialyl glycans were most abundant in all four glycoproteins, followed by neutral glycans. Disialyl glycans were lowest in ovotransferrin, and highest in ovomucoid. Triantennary structures with bisecting GlcNAc were predominant in ovotransferrin, and tetra-antennary (with and without bisecting GlcNAc-containing) structures were predominant in other glycoproteins. Penta-antennary structures (with a sialic acid and without bisecting GlcNAc residue) were also found in small quantities in all four glycoproteins. In contrast to the chicken egg white counterparts, which contain mostly high mannose and hybrid types, all N-glycan structures in the major pigeon egg white glycoproteins are complex type.