N-glycan biosignatures as a potential diagnostic biomarker for earlystage pancreatic cancer

BACKGROUND Pancreatic ductal adenocarcinoma(PDAC)has a poor prognosis,with a 5-year survival rate of less than 10%,owing to its late-stage diagnosis.Early detection of pancreatic cancer(PC)can significantly increase survival rates.AIM To identify the serum biomarker signatures associated with early-stage PDAC by serum N-glycan analysis.METHODS An extensive patient cohort was used to determine a biomarker signature,in-cluding patients with PDAC that was well-defined at an early stage(stages I and II).The biomarker signature was derived from a case-control study using a case-cohort design consisting of 29 patients with stage I,22 with stage II,4 with stage III,16 with stage IV PDAC,and 88 controls.We used multiparametric analysis to identify early-stage PDAC N-glycan signatures and developed an N-glycan sig-nature-based diagnosis model called the“Glyco-model”.RESULTS The biomarker signature was created to discriminate samples derived from patients with PC from those of controls,with a receiver operating characteristic area under the curve of 0.86.In addition,the biomarker signature combined with cancer antigen 19-9 could discriminate patients with PDAC from controls,with a receiver operating characteristic area under the curve of 0.919.Glyco-model demonstrated favorable diagnostic performance in all stages of PC.The diagnostic sensitivity for stage I PDAC was 89.66%.Core Tip:This study employed a patient cohort to investigate the N-glycan signature of early-stage pancreatic cancer(PC).Serum N-glycans analysis was conducted to identify the serum biomarker signature associated with early-stage pancreatic ductal adenocarcinoma(PDAC),resulting in the identification of nine early-stage PDAC N-glycan signatures.Subsequently,utilizing these biosignatures,a diagnostic model named the“Glyco-model”was developed,demonstrating promising diagnostic performance across all stages of PC.The study revealed that the diagnostic sensitivity for stage I PDAC was determined to be 89.66%.Consequently,this diagnostic model exhibits potential as a prospective strategy for the early detection of PDAC.

A Nested Case-Control Study to Explore the Association between Immunoglobulin G N-glycans and Ischemic Stroke

Objective This study prospectively investigates the association between immunoglobulin G(IgG)N-glycan traits and ischemic stroke(IS) risk.Methods A nested case-control study was conducted in the China suboptimal health cohort study,which recruited 4,313 individuals in 2013–2014. Cases were identified as patients diagnosed with IS, and controls were 1:1 matched by age and sex with cases. Ig G N-glycans in baseline plasma samples were analyzed.Results A total of 99 IS cases and 99 controls were included, and 24 directly measured glycan peaks(GPs) were separated from Ig G N-glycans. In directly measured GPs, GP4, GP9, GP21, GP22, GP23, and GP24 were associated with the risk of IS in men after adjusting for age, waist and hip circumference,obesity, diabetes, hypertension, and dyslipidemia. Derived glycan traits representing decreased galactosylation and sialylation were associated with IS in men(FBG2S2/(FBG2 + FBG2S1 + FBG2S2): odds ratio(OR) = 0.92, 95% confidence interval(CI): 0.87–0.97;G1n: OR = 0.74, 95% CI: 0.63–0.87;G0n: OR =1.12, 95% CI: 1.03–1.22). However, these associations were not found among women.Conclusion This study validated that altered Ig G N-glycan traits were associated with incident IS in men, suggesting that sex discrepancies might exist in these associations.

An innovative method used for the identification of N-glycans on soybean allergenβ-conglycinins

β-Conglycinin is one of the major allergens existed in soybean.N-Glycans attached to theβ-conglycinin influenced the immunoreactivity and antigen presenting efficiency ofβ-conglycinin.In this study,we described a new method used to release and collect the N-glycans fromβ-conglycinin,and the N-glycans existed in linear epitopes ofβ-conglycinin were identified.Glycopeptides hydrolyzed fromβ-conglycinin were purified by cotton hydrophilic chromatography.Trifluoromethylsulfonic acid was then used to release glycans from glycopeptides,and new glycopeptides containing one single N-acety1-D-glucosamine(G1 cNAc)moiety were then utilized for mass spectrometry.Five glycosylation sites(Asn-199,Asn-455,Asn-215,Asn-489 and Asn-326)and 22 kinds of glycopeptides were identified.It is noteworthy that the peptide VVN^(#)ATSNL(where^(#)represents for the glycosylation site)was analyzed to be both glycopeptide and linear epitope.Our results provided a new method for the N-glycoform analysis of food allergens,and laid a foundation for understanding the relationship between glyco sylation and food allergy.

Serum N-glycan markers for diagnosing liver fibrosis induced by hepatitis B virus

BACKGROUND Hepatitis B virus (HBV) infection is the primary cause of hepatitis with chronic HBV infection,which may develop into liver fibrosis,cirrhosis and hepatocellular carcinoma.Detection of early-stage fibrosis related to HBV infection is of great clinical significance to block the progression of liver lesion.Direct liver biopsy is regarded as the gold standard to detect and assess fibrosis;however,this method is invasive and prone to clinical sampling error.In order to address these issues,we attempted to find more convenient and effective serum markers for detecting HBV-induced early-stage liver fibrosis.AIM To investigate serum N-glycan profiling related to HBV-induced liver fibrosis and verify multiparameter diagnostic models related to serum N-glycan changes.METHODS N-glycan profiles from the sera of 432 HBV-infected patients with liver fibrosis were analyzed.Significant changed N-glycan levels (peaks)(P <0.05) in differentfibrosis stages were selected in the modeling group,and multiparameter diagnostic models were established based on changed N-glycan levels by logistic regression analysis.The receiver operating characteristic (ROC) curve analysis was performed to evaluate diagnostic efficacy of N-glycans models.These models were then compared with the aspartate aminotransferase to platelet ratio index (APRI),fibrosis index based on the four factors (FIB-4),glutamyltranspeptidase platelet albumin index (S index),GlycoCirrho-test,and GlycoFibro-test.Furthermore,we combined multiparameter diagnostic models with alanine aminotransferase (ALT) and platelet (PLT) tests and compared their diagnostic power.In addition,the diagnostic accuracy of N-glycan models was also verified in the validation group of patients.RESULTS Multiparameter diagnostic models constructed based on N-glycan peak 1,3,4and 8 could distinguish between different stages of liver fibrosis.The area under ROC curves (AUROCs) of Model A and Model B were 0.890 and 0.752,respectively differentiating fibrosis F0-F1 from F2-F4,and F0-F2 from F3-F4,and surpassing other serum panels.However,AUROC (0.747) in Model C used for the diagnosis of F4 from F0-F3 was lower than AUROC (0.795) in FIB-4.In combination with ALT and PLT,the multiparameter models showed better diagnostic power (AUROC=0.912,0.829,0.885,respectively) when compared with other models.In the validation group,the AUROCs of the three combined models (0.929,0.858,and 0.867,respectively) were still satisfactory.We also applied the combined models to distinguish adjacent fibrosis stages of 432patients (F0-F1/F2/F3/F4),and the AUROCs were 0.917,0.720 and 0.785.CONCLUSION Multiparameter models based on serum N-glycans are effective supplementary markers to distinguish between adjacent fibrosis stages of patients caused by HBV,especially in combination with ALT and PLT.

Comparing different domains of analysis for the characterisation of N-glycans on monoclonal antibodies

With the size of the biopharmaceutical market exponentially increasing,there is an aligned growth in the importance of data-rich analyses,not only to assess drug product safety but also to assist drug development driven by the deeper understanding of structure/function relationships.In monoclonal antibodies,many functions are regulated by N-glycans present in the constant region of the heavy chains and their mechanisms of action are not completely known.The importance of their function focuses analytical research efforts on the development of robust,accurate and fast methods to support drug development and quality control.Released N-glycan analysis is considered as the gold standard for glycosylation characterisation;however,it is not the only method for quantitative analysis of glycoform heterogeneity.In this study,ten different analytical workflows for N-glycan analysis were compared using four monoclonal antibodies.While observing good comparability between the quantitative results generated,it was possible to appreciate the advantages and disadvantages of each technique and to summarise all the observations to guide the choice of the most appropriate analytical workflow according to application and the desired depth of data generated.

Association between IgG N-glycans and Nonalcoholic Fatty Liver Disease in Han Chinese

Nonalcoholic fatty liver disease（NAFLD） is a major public health issue worldwide. Immunoglobulin G（IgG） N-glycans are associated with risk factors for NAFLD, such as obesity and diabetes. A cross-sectional study involving 500 Han Chinese adults recruited from a community in Beijing was carried out to explore the association between IgG N-glycans and NAFLD. IgG N-glycosylation was significantly associated with NAFLD, with the disease showing a negative correlation with galactosylation（GP14, GP14n, and G2n）, positive correlation with fucosylation（FBG2n/G2n）, and positive correlation with bisecting N-acetylglucosamine（Glc NAc） [FBG2n/FG2n and FBG2n/（FG2n＋FBG2n）], after controlling age, gender, and prevalence of obesity, type 2 diabetes mellitus, hypertension, and hyperlipidemia. In other words, the present study showed a possible association between NAFLD and the loss of galactose and elevations of fucose and bisecting GlcNAc. Aberrant IgG glycosylation might therefore be a potential biomarker for the primary or secondary prevention of NAFLD.

N-glycans released from glycoproteins using a commercial kit and comprehensively analyzed with a hypothetical database

The glycosylation of proteins is responsible for their structural and functional roles in many cellular activities.This work describes a strategy that combines an efficient release, labeling and liquid chromatography–mass spectral analysis with the use of a comprehensive database to analyze N-glycans. The analytical method described relies on a recently commercialized kit in which quick deglycosylation is followed by rapid labeling and cleanup of labeled glycans. This greatly improves the separation, mass spectrometry（MS） analysis and fluorescence detection of N-glycans. A hypothetical database, constructed using Glyc Resoft, provides all compositional possibilities of N-glycans based on the common sugar residues found in N-glycans. In the initial version this database contains ＆gt; 8,700 N-glycans, and is compatible with MS instrument software and expandable. N-glycans from four different well-studied glycoproteins were analyzed by this strategy. The results provided much more accurate and comprehensive data than that had been previously reported. This strategy was then used to analyze the N-glycans present on the membrane glycoproteins of gastric carcinoma cells with different degrees of differentiation. Accurate and comprehensive N-glycan data from those cells was obtained efficiently and their differences were compared corresponding to their differentiation states. Thus, the novel strategy developed greatly improves accuracy, efficiency and comprehensiveness of N-glycan analysis.

鹅颈藤壶多糖提取、理化性质及N-糖链表达谱分析研究

本文以南海海域鹅颈藤壶(Lepas anatifera)为原料,提取鹅颈藤壶背甲与肌肉质柄中的多糖,基于其基本理化性质的分析,比较不同生长时期鹅颈藤壶N-糖链表达谱的差异性。经过脱脂、碱水解/蛋白酶解、乙醇沉淀方法提取得到粗多糖;利用高效液相色谱法、高效凝胶渗透色谱法、苯酚-硫酸法、考马斯亮蓝法对其单糖组成、分子量分布、总糖含量及蛋白质含量进行分析;采用液质分析(PGC-ESI-MS/MS)方法对鹅颈藤壶成体(A-GB)与幼体(L-GB)肌肉质柄中N-糖链进行分析并比较。表明肌肉质柄中多糖分子量为18.40 kDa;总糖含量为11.99%,蛋白质含量60.14%,富含甘露糖、葡萄糖、氨基半乳糖,其中甘露糖的含量高达80%以上。在鹅颈藤壶成体与幼体中均鉴定得到26条N-糖链,成体中高甘露糖型N-糖链占总糖链的20.81%,且相对丰度较高的糖型组成为F_(1)H_(3)N_(2)(39.06%)、F_(1)H_(3)N_(3)(24.44%)、H_(3)N_(3)(9.35%);幼体中高甘露糖型N-糖链占总糖链的52.17%,相对丰度较高的糖型组成为F_(1)H_(3)N_(2)(21.65%)、H_(6)N_(2)(15.93%)、H_(5)N_(2)(14.75%)。鹅颈藤壶多糖是一类N-糖基化的蛋白复合物,推测N-糖链在鹅颈藤壶长发育过程中发挥着至关重要的作用,可能高甘露糖型N-糖链与其附着黏附能力密切相关。

源于细菌Dyella caseinilytica的新型N-糖酰胺酶的特性及其功能分析

N-糖酰胺酶(N-glycosidase,PNGase)是一种糖苷水解酶,主要功能为释放糖肽或糖蛋白上的N-糖链,在食品、生物医药等领域中具有重要的应用价值。目前,商业化的PNGase在使用过程中具有一定的局限性,因此,开发性能优良的新型PNGase具有研究意义。该研究在细菌Dyella caseinilytica中利用编码PNGase的基因,通过在大肠杆菌中进行重组表达,成功获得一种新型PNGase,命名为PNGase Dc,该酶分子质量为63.01 kDa。之后对其酶学特性、功能和应用潜力进行分析。酶学特性结果表明,PNGase Dc的最适pH和温度分别为2.0和37℃,酶促反应无金属离子依赖性;此外,该酶稳定性优良,在4℃下保存45 d仍能维持最高活性;分子对接结果表明,PNGase Dc与底物N′N-二乙酰壳二糖的相互作用力以氢键和范德华力为主;定点突变证明,Asp102和Glu236是影响重组PNGase Dc活性的关键氨基酸;PNGase Dc对标准糖蛋白辣根过氧化物酶和牛乳铁蛋白均具有良好的去糖基化效果;最后,以拟南芥和小鼠血浆作为底物评估PNGase Dc应用潜力,证实PNGase Dc在动植物源糖蛋白的研究中具有一定的应用潜力。综上所述,该研究为动植物源糖蛋白的研究提供了一个新的工具酶PNGase Dc,并为该酶的开发利用奠定理论基础。

Trimming of N-Glycans by the Golgi-Localized α-1,2-Mannosidases, MNS1 and MNS2, Is Crucial for Maintaining RSW2 Protein Abundance during Salt Stress in Arabidopsis

Asparagine （Asn/N）-Iinked glycans are important for protein folding, trafficking, and endoplasmic reticulum-associated degradation in eukaryotes. The maturation of glycoproteins involves the trimming of mannosyl residues by mannosidases and addition of other sugar molecules to three-branched N-glycans in the Golgi. However, the biological importance of Golgi-mediated mannose trimming is not fully understood. Here, we show that abolishment of two functionally redundant mannosidases, MNS1 and MNS2, responsible for α-1,2-mannose trimming on the A and C branches of plant N-glycans lead to severe root growth inhibition under salt stress conditions in Arabidopsis. In contrast, mutants with defects in the biosynthesis of the oligosaccharide precursor displayed enhanced salt tolerance in the absence of mannose trimming. However, mutation in EBS3, which is required for the formation of the branched N-glycan precursor, suppressed the salt-sensitive phenotype of mnsl mns2 double mutant. Interestingly, we observed that cellulose biosynthesis was compromised in mnsl mns2 roots under high salinity. Consistently, abundance of a membrane anchored endo-13-1,4-endoglucanase （RSW2/KOR） that plays a key role in cellulose biosynthesis and its mutant variant rsw2-1 were modulated by α-1,2-mannose trimming under salt stress. Overexpression of RSW2 could partially rescue the salt-sensitive phenotype of mnsl mns2. Taken together, these results suggest that MNS1/2-mediated mannose trimming of N-glycans is crucial in modulating glycoprotein abundance to withstand salt stress in plants.

Growth phase-dependent expression of proteins with decreased plant-specific N-glycans and immunogenicity in tobacco BY2 cells

Plants possess some desirable characteristics to synthesize recombinant glycoproteins for pharma-ceutical application.However,the mammalian glycoproteins produced in plants are somewhat different from their natural counterparts in terms of N-glycoforms.The immunogenicity of plant-specific glyco-epitopes is the major concern in human therapy.Here,the distribution of N-glycans in different growth phases of tobacco BY2 cells and their immunogenicity in mice were determined.It was ob-served that the percentage of β1,2-xylose and α1,3-fucose in proteins of growing cells increased and the corresponding protein extracts caused accelerated immune response in mice.Based on this observation,the recombinant erythropoietin in BY2 cells was expressed and characterized,and Western blot analysis showed that the recombinant erythropoietin contained a relatively small amount of plant-specific glyco-epitopes in the early phase of culture growth.This study may provide a simple but effective strategy for the production of therapeutic glycoproteins with human-like N-glycan structures in plant hosts to avoid a great allergenic risk.

N-乙酰氨基葡萄糖苷内切酶的功能与机制

N-乙酰氨基葡萄糖苷内切酶(endo-beta-N-acetylglucosaminidase,ENGase)广泛分布于各种生物中,主要通过降解错误折叠的糖蛋白,参与细胞和生命的调控。ENGase也是糖链编辑的有效工具酶,可专一性水解游离寡糖链及糖肽或糖蛋白上核心五糖的N-乙酰氨基葡萄糖(GlcNAc)之间的β-14糖苷键。其水解产物是寡糖链和一个GlcNAc,或带有一个GlcNAc的糖肽或糖蛋白。本文对ENGase的发现、分布、蛋白质结构、酶学反应及生物学功能进行阐述,为ENGase的生物学研究提供思路,为糖生物学与糖组学的应用研究奠定基础。

Two-step derivatization and mass spectral distinction of α2,3 and α2,6sialic acid linkages on N-glycans by MALDI-TOF

Sialylation is one of important glycosylation in human beings and plays an important role in cancer development. α2,3-Linked and α2,6-linked sialic acids are normally observed on the end of N-glycans and have different functions. Derivatization on sialic acid was designed to detect the different linkages by MALDI-TOF MS. In this study, a two-step derivatization by dimethylamine and ammonium hydroxide was improved to modify the sialic acid and made it easier to detect the different linkages of sialic acids on MALDI-TOF MS. Using this derivatization method, specific sialic acids linkages on N-glycans of protein samples such as fetuin and lactoferrin were detected. For complex cell samples, increased a2,3-linked and a2,6-linked sialic acids on bi-antennary and tri-antennary N-glycans were observed in A549 cells induced by hypoxia environment. Taken together, our two-step derivatization of sialic acids offers a simple and accurate way to detect specific linkages on N-glycans with MALDI-TOF mass spectrometer.

N-糖基化修饰的神经细胞生物学及其在神经系统疾病中的作用

神经发育和神经系统功能受到包括环境、遗传和表观遗传在内的多种因素的调控。N-糖基化修饰是由糖基化转移酶催化形成的蛋白质翻译后修饰,参与多种生物学过程。在神经系统中,N-糖基化修饰高丰度存在,调控神经突触的发育、成熟和胶质细胞的炎症反应。异常N-糖基化修饰与阿尔茨海默病、先天性糖基化障碍、精神分裂症和癫痫等多种神经系统疾病密切相关。本文中我们综述了N-糖基化修饰的神经细胞生物学功能及其在神经系统疾病中的作用和机制。

血清N-聚糖生物标志物诊断ALT水平正常慢性乙型肝炎患者显著肝纤维化和肝硬化的临床意义

本研究目的是探讨血清N-聚糖模型在285例丙氨酸转移酶(alanine aminotransferase,ALT)水平正常(<40 U·L^(-1))的慢性乙型肝炎(慢性乙肝)患者中诊断显著肝纤维化和肝硬化的临床意义。入组患者均进行肝组织活检,并使用Ishak评分系统评估患者肝组织纤维化程度。应用基于DNA测序仪的荧光糖电泳技术检测患者血清N-聚糖图谱,每例患者的血清样本中共鉴定出9个N-聚糖峰。利用机器学习算法,即随机森林(random forest,RF)构建更理想的血清N-聚糖模型,以诊断显著肝纤维化(≥F3)和肝硬化(≥F5),并比较血清N-聚糖模型和其他纤维化标志物的诊断效能。肝组织活检结果显示,有显著肝纤维化和肝硬化患者分别占63.86%(182/285)和16.49%(47/285),有显著炎症患者为4.91%(14/285)。血清N-聚糖RF-A模型具有很好的诊断显著肝纤维化(≥F3)的效能,其受试者工作特征曲线下面积(area under receiver operating characteristic curve,AUROC)为0.94,与肝活检的符合率为90.45%。在诊断肝硬化(≥F5)时,血清N-聚糖RF-B模型的AUROC为0.97,与肝组织活检的符合率为88.94%。血清N-聚糖模型(RF-A和RF-B)的诊断效能优于肝硬度值测量(liver stiffness measurement,LSM)、基于4因子的纤维化指数(fibrosis index based on the four factors,FIB-4)和天冬氨酸转氨酶与血小板比率指数(aspartate aminotransferase-to-platelet ratio index,APRI)。在ALT水平正常的慢性乙肝患者中,血清N-聚糖模型可作为诊断显著肝纤维化或肝硬化的潜在生物标志物。

可去除染料--N-聚糖多方法深入分析中的缺失环节

As the roles of glycans in health and disease continue to be unraveled,it is becoming apparent that glycans’immense complexity cannot be ignored.To fully delineate glycan structures,we developed an integrative approach combining a set of cost-effective,widespread,and easy-to-handle analytical methods.The key feature of our workflow is the exploitation of a removable fluorescent label—exemplified by 9-fluorenylmethyl chloroformate(Fmoc)—to bridge the gap between diverse glycoanalytical methods,especially multiplexed capillary gel electrophoresis with laser-induced fluorescence detection(xCGELIF)and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOFMS).Through the detailed structural analysis of selected,dauntingly complex N-glycans from chicken ovalbumin,horse serum,and bovine transferrin,we illustrate the capabilities of the presented strategy.Moreover,this approach“visualizes”N-glycans that have been difficult to identify thus far—such as the sulfated glycans on human immunoglobulin A—including minute changes in glycan structures,potentially providing useful new targets for biomarker discovery.

系统性红斑狼疮患者的血清IgG糖链特征

系统性红斑狼疮(systemic lupus erythematosus,SLE)是一种发病机制不明、临床表型异质性大的自身免疫性疾病。目前已有的SLE血清生物标志物灵敏度或特异性有限,使得SLE的早期精准诊断存在困难。在本研究中,通过对389例SLE患者及304例健康对照者进行深入的糖组学分析,鉴定出血清免疫球蛋白G(IgG)上的两种N-糖链能够作为SLE的诊断生物标志物。在其他易与SLE混淆的系统性自身免疫性疾病(如类风湿性关节炎、原发性干燥综合征或系统性硬化症)中,这两种生物标志物没有出现显著变化,提示这两种N-糖链生物标志物对诊断SLE具有特异性。值得注意的是,这两种N-糖链生物标志物被证明是自身抗体非依赖性的,并且适用于所有阶段的SLE患者。基于片段特异性糖链分析和糖肽分析,发现这两种N-糖链生物标志物位于IgG上的Fc区域,并与疾病活动性密切相关。而酶学分析结果则提示,SLE患者体内一系列糖转移酶的失调可能是观察到的糖链产生变化的原因。研究结果为基于血清IgG糖基化的高效人群筛查和SLE潜在的新致病因素提供了新的思路。

Site-specific N-glycosylation characterization and allergenicity analysis of globulin-1 S allele from wheat

N-glycans in many proteins are of great concern because of their strong association with food allergies. Triticum aestivum(bread wheat), a major food crop, is known as one of the “Big Eight” allergenic groups. However, little research has been done about N-glycans in wheat glycoproteins. In this study, a soluble wheat glycoprotein was purified from wheat and further identified as globulin-1 S allele(GSA). The wheat GSA displayed significant IgE-binding activity. Moreover, one N-glycosylation site and 6 kinds of N-glycans were identified by mass spectrometry, including 3 high mannose types and 3 complex types. Furthermore, the IgE-binding activity of wheat GSA is proved to be reduced by the removal of N-glycan, thermal treatment(temperatures > 80 ℃), and strong acidic treatment(pH 3.0). These findings would provide a better understanding of the effects of N-glycosylation, thermal treatment, and acidic treatment on the molecular characteristics of GSA, and further provide new insights into the development of hypoallergenic wheat products.

乳源N-聚糖的结构与功能研究进展

论述了乳源N-聚糖的结构特性、不同物种间结构与含量的比较(人乳、牛乳和山羊乳)、生物学功能,以及近年来在婴儿食品中的应用。通过对相关文献的梳理,指出牛乳和山羊乳源N-聚糖与母乳N-聚糖具有同源性,有望作为一种食品配料补充到婴儿配方奶粉中,起到促进肠道有益微生物定殖、抑制致病菌生长、抑制病原体黏附、抗炎、免疫调节、促进大脑发育等作用。未来可就提高乳源N-聚糖富集程度及其在婴儿配方奶粉中的作用机制等方面开展深入研究,以进一步拓展乳源N-聚糖在婴儿食品中的应用。

基于质谱的N-糖蛋白分析进展

N-连接糖基化是蛋白质上常见的翻译后修饰,在修饰位点上具有跟其他小分子修饰(如甲基化、乙酰化、磷酸化)同样的宏观不均一性,也就是蛋白质氨基酸序列上具有多个潜在的修饰位点。但相对于小分子修饰单一的结构,N-糖基化修饰具有来自不同单糖组成,序列结构、链接结构、异头异构,立体构象等多个结构维度的数以万计的结构。这使得N-糖基化在修饰位点上具有额外的微观不均一性,也就是说同一个N-糖基化位点可以以一定的化学计量比修饰不同的糖链。N-糖基化修饰以位点和结构特异的方式调控N-糖蛋白的结构和功能,疾病条件下差异表达的N-糖基化需通过位点和结构特异的定量分析来表征。本文主要介绍最新发展水平的基于质谱的位点和结构特异定量N-糖蛋白质组学及在生物医学中的应用。