Relative quantification of plasma N-glycans in type II congenital disorder of glycosylation patients by mass spectrometry

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Liquid chromatography and capillary electrophoresis in glycomic and glycoproteomic analysis

Glycosylation is one of the most significant and abundant post-translational modifications in cells. Glycomic and glycoproteomic analyses involve the characterization of oligosaccharides (glycans) conjugated to proteins. Glycomic and glycoproteomic analysis is highly challenging because of the large diversity of structures, low abundance, site-specific heterogeneity, and poor ionization efficiency of glycans and glycopeptides in mass spectrometry (MS). MS is a key tool for characterization of glycans and glycopeptides. However, MS alone does not always provide full structural and quantitative information for many reasons, and thus MS is combined with some separation technique. This review focuses on the role of separation techniques used in glycomic and glycoproteomic analyses, liquid chromatography and capillary electrophoresis. The most important separation conditions and results are presented and discussed.

Graphical abstract

Siblings with MAN1B1-CDG Showing Novel Biochemical Profiles

Congenital disorders of glycosylation (CDG), inherited metabolic diseases caused by defects in glycosylation, are characterized by a high frequency of intellectual disability (ID) and various clinical manifestations. Two siblings with ID, dysmorphic features, and epilepsy were examined using mass spectrometry of serum transferrin, which revealed a CDG type 2 pattern. Whole-exome sequencing showed that both patients were homozygous for a novel pathogenic variant of MAN1B1 (NM_016219.4:c.1837del) inherited from their healthy parents. We conducted a HPLC analysis of sialylated N-linked glycans released from total plasma proteins and characterized the α1,2-mannosidase I activity of the lymphocyte microsome fraction. The accumulation of monosialoglycans was observed in MAN1B1-deficient patients, indicating N-glycan-processing defects. The enzymatic activity of MAN1B1 was compromised in patient-derived lymphocytes. The present patients exhibited unique manifestations including early-onset epileptic encephalopathy and cerebral infarction. They also showed coagulation abnormalities and hypertransaminasemia. Neither sibling had truncal obesity, which is one of the characteristic features of MAN1B1-CDG.

Translational balancing questioned: Unaltered glycosylation during disulfiram treatment in mannosyl-oligosaccharide alpha-1,2-mannnosidase-congenital disorders of glycosylation (MAN1B1-CDG)

MAN1B1-CDG is a multisystem disorder caused by mutations in MAN1B1, encoding the endoplasmic reticulum mannosyl-oligosaccharide alpha-1,2-mannnosidase. A defect leads to dysfunction within the degradation of misfolded glycoproteins. We present two additional patients with MAN1B1-CDG and a resulting defect in endoplasmic reticulum-associated protein degradation. One patient (P2) is carrying the previously undescribed p.E663K mutation. A therapeutic trial in patient 1 (P1) using disulfiram with the rationale to generate an attenuation of translation and thus a balanced, restored ER glycoprotein synthesis failed. No improvement of the transferrin glycosylation profile was seen.

Identification of Differential N-Glycan Compositions in the Serum and Tissue of Colon Cancer Patients by Mass Spectrometry

Simple Summary

Incidence of colorectal cancer (CRC) has been rising in Brazil. To date, no reliable biomarker has been described in CRC for diagnosis and prognosis. Modifications in the N-glycosylation profile are usually associated with many cancers, as CRC. In turn, mass spectrometry (MS)-based methods are the most accurate technology in quantification of N-glycans. Therefore, we described a unique pattern of compositions altered in serum and tissues of stages II and III colon cancer patients, identified by MALDI-TOF/MS and LC-MS technology. N-glycans were mostly found decreased in serum whilst oligomannosidic, hypogalactosylated, and tetra-antennary forms were overexpressed in tumor tissues. Total N-glycome in serum of cancer patients was different from the profile found in serum of healthy individuals. Strikingly, no correlation between tissue N-glycosylation profile and serum profile was observed in cancer patients, posing the question where these compositions are originated from.

Abstract

Colorectal cancer (CRC) ranks second as the leading cause of cancer-related deaths worldwide. N-glycosylation is one of the most common posttranslational protein modifications. Therefore, we studied the total serum N-glycome (TSNG) of 13 colon cancer patients compared to healthy controls using MALDI-TOF/MS and LC-MS. N-glycosylation of cancer tumor samples from the same cohort were further quantified using a similar methodology. In total, 23 N-glycan compositions were down-regulated in the serum of colon cancer patients, mostly galactosylated forms whilst the mannose-rich HexNAc2Hex7, the fucosylated bi-antennary glycan HexNAc4Hex5Fuc1NeuAc2, and the tetra-antennary HexNAc6Hex7NeuAc3 were up-regulated in serum. Hierarchical clustering analysis of TSNG correctly singled out 85% of the patients from controls. Albeit heterogenous, N-glycosylation of tumor samples showed overrepresented oligomannosidic, bi-antennary hypogalactosylated, and branched compositions related to normal colonic tissue, in both MALDI-TOF/MS and LC-MS analysis. Moreover, compositions found upregulated in tumor tissue were mostly uncorrelated to compositions in serum of cancer patients. Mass spectrometry-based N-glycan profiling in serum shows potential in the discrimination of patients from healthy controls. However, the compositions profile in serum showed no parallel with N-glycans in tumor microenvironment, which suggests a different origin of compositions found in serum of cancer patients.

HILIC-UPLC-MS for high throughput and isomeric N-glycan separation and characterization in Congenital Disorders Glycosylation and human diseases

N-glycan analyses may serve uncovering disease-associated biomarkers, as well as for profiling distinctive changes supporting diagnosis of genetic disorders of glycan biosynthesis named congenital disorders of glycosylation (CDG). Strategies based on liquid chromatography (LC) preferentially coupled to electrospray ionization (ESI) - mass spectrometry (MS) have emerged as powerful analytical methods for N-glycan identification and characterization. To enhance detection sensitivity, glycans are commonly labelled with a functional tag prior to LC-MS analysis. Since most derivatization techniques are notoriously time-consuming, some commercial analytical kits have been developed to speed up N-deglycosylation and N-glycan labelling of glycoproteins of pharmaceutical and biological interest such as monoclonal antibodies (mAbs). We exploited the analytical capabilities of RapiFluor-MS (RFMS) to perform, by a slightly modified protocol, a detailed N-glycan characterization of total serum and single serum glycoproteins from specific patients with CDG (MAN1B1-CDG, ALG12-CDG, MOGS-CDG, TMEM199-CDG). This strategy, accomplished by Hydrophilic Interaction Chromatography (HILIC)-UPLC-ESI-MS separation of the RFMS derivatized N-glycans, allowed us to uncover structural details of patients serum released N-glycans, thus extending the current knowledge on glycan profiles in these individual glycosylation diseases. The applied methodology enabled to differentiate in some cases either structural isomers and isomers differing in the linkage type. All the here reported applications demonstrated that RFMS method, coupled to HILIC-UPLC-ESI-MS, represents a sensitive high throughput approach for serum N-glycome analysis and a valuable option for glycan detection and separation particularly for isomeric species.

Low Collision Energy Fragmentation in Structure-Specific Glycoproteomics Analysis

Glycosylation is a major post-translational modification of proteins that regulates many biological processes including protein folding, structure stability, receptor activation, and immune responses. The glycans attached to proteins represent an important determinant of the protein interaction-specificity and maintain the 3D structure of proteins. Mass spectrometry (MS) is one of the most efficient tools used in the current studies of glycoproteins and structure of their glycoforms. Collision energy (CE) is a crucial instrument parameter that can be exploited to improve structural resolution because different linkages of glycan units show different stabilities under CID/HCD fragmentation. Here we report the utility of CE modulation for qualitative and quantitative analysis of site- and structure-specific glycoforms of proteins. Using CE modulation, we were able to break selectively specific glycan linkages on intact glycopeptides and get, to some degree, structure-specific mass spectrometric signals. Structure- and CE-specific oxonium ions provide sufficient information for the resolution of outer arm structure motifs with recognized biological functions. The complementary Y-ions, generated under optimized low CE (soft) conditions, provide additional structural information including features specific to the chitobiose core. This methodology of multiple CE fragmentation without merging spectral information can significantly improve confidence of glycopeptide identification and structural resolution by providing additional information to the established glycopeptide-search algorithms and tools.