Quantitative mass spectrometric analysis of glycoproteins combined with enrichment methods

Electrospun Fiber Membrane with the Dual Affinity of Chelation and Covalent Interactions for the Efficient Enrichment of Glycoproteins

As important biomarkers of many diseases, glycoproteins are of great significance to biomedical science. It is essential to develop efficient glycoprotein enrichment platforms and investigate their adsorption mechanism. In this work, a conspicuous enrichment strategy for glycoproteins was developed by using an electrospun fiber membrane wrapped with polydopamine (PDA) and modified with 3-aminophenylboronic acid and nickel ions, named PAN/DA@PDA@APBA/Ni. The enrichment characteristics of PAN/DA@PDA@APBA/Ni toward glycoproteins were explored through adsorption behavior. Thanks to the existence of two sites of interaction (metal ion chelation and boronate affinity), PAN/DA@PDA@APBA/Ni exhibited significant enrichment capacity for glycoproteins, ovalbumin (604.6 mg/g), and human immunoglobulin G (331.0 mg/g). The adsorption kinetic results of glycoprotein ovalbumin on PAN/DA@PDA@APBA/Ni conform to the pseudo-first-order kinetic model in the first adsorption stage, while the second half adsorption stage is more in line with the pseudo-second-order kinetic model. Moreover, the physical characteristics of PAN/DA@PDA@APBA/Ni and subsequent adsorption experiments on electrospun fiber modified with only phenylboronic acid or nickel ions both confirmed two sites of interaction (metal ion chelation and boronate affinity, respectively). Furthermore, a stepwise elution method with dual-affinity interaction was designed and successfully applied to enrich glycoproteins in real biological samples. This work provides an idea for sample pretreatment, especially for the design of dual-affinity materials in glycoproteins enrichment.

N-linked glycoproteome analysis reveals central glycosylated proteins involved in response to wheat yellow mosaic virus in wheat

Glycosylation is an important proteins post-translational modification and is involved in protein folding, stability and enzymatic activity, which plays a crucial role in regulating protein function in plants. Here, we report for the first time on the changes of N-glycoproteome in wheat response to wheat yellow mosaic virus (WYMV) infection. Quantitative analyses of N-linked glycoproteome were performed in wheat without and with WYMV infection by ZIC-HILIC enrichment method combined with LC-MS/MS. Altogether 1160 N-glycopeptides and 971 N-glycosylated sites corresponding to 734 N-glycoproteins were identified, of which 64 N-glycopeptides and 64 N-glycosylated sites in 60 N-glycoproteins were significantly differentially expressed. Two conserved typical N-glycosylation motifs N-X-T and N-X-S and a nontypical motifs N-X-C were enriched in wheat. Gene Ontology analysis showed that most differentially expressed proteins were mainly enriched in metabolic process, catalytic activity and response to stress. Kyoto Encyclopedia of Genes and Genomes analysis indicated that two significantly changed glycoproteins were specifically related to plant-pathogen interaction. Furthermore, we found that over-expression of TaCERK reduced WYMV accumulation. Glycosylation site mutation further suggested that N-glycosylation of TaCERK could regulate wheat resistance to WYMV. This study provides a new insight for the regulation of protein N-glycosylation in defense response of plant.

Isolation of Momordica charantia seed lectin and glycosidases from the protein bodies: Lectin-glycosidase (β-hexosaminidase) protein body membrane interaction reveals possible physiological function of the lectin

Momordica charantia seeds are known to contain a galactose specific lectin that has been well characterized. Seed extracts also contain glycosidases such as the β-hexosaminidase, α-mannosidase and α-galactosidase. In the present study, lectin was affinity purified from the seed extracts and protein bodies isolated by sucrose density gradient centrifugation. From the protein bodies, lectin was identified and β-hexosaminidase was isolated by lectin affinity chromatography and subsequently separated from other glycosidases by gel filtration. In the native PAGE, the purified β-hexosaminidase migrated as a single band with a molecular weight of ∼235 kDa and by zymogram analysis using 4-methylumbelliferyl N-acetyl-β-D-glucosaminide substrate it was confirmed as β-hexosaminidase. Under reducing conditions in SDS-PAGE, the purified enzyme dissociated into three bands (Mr 33, 20 and 15 kDa). The prominent bands (20 and 15 kDa) showed immunological cross-reactivity with the human Hexosaminidase B antibody in a western blot experiment. In gel digestion of the purified enzyme, followed by proteomic analysis using tandom MS/MS revealed sequence identity as compared to the genomic sequence of the Momordica charantia with a score of 57 (24% sequence coverage). Additionally, by CD analysis the purified β-hexosaminidase showed 39.1% of α-helix. Furthermore, secondary structure variations were observed in presence of substrate, lectin and at different pH values. Protein body membrane prepared from the isolated protein bodies showed a pH dependent interaction with the purified lectin and mixture of glycosidases.

Bottom-Up Proteomics: Advancements in Sample Preparation

Liquid chromatography–tandem mass spectrometry (LC–MS/MS)-based proteomics is a powerful technique for profiling proteomes of cells, tissues, and body fluids. Typical bottom-up proteomic workflows consist of the following three major steps: sample preparation, LC–MS/MS analysis, and data analysis. LC–MS/MS and data analysis techniques have been intensively developed, whereas sample preparation, a laborious process, remains a difficult task and the main challenge in different applications. Sample preparation is a crucial stage that affects the overall efficiency of a proteomic study; however, it is prone to errors and has low reproducibility and throughput. In-solution digestion and filter-aided sample preparation are the typical and widely used methods. In the past decade, novel methods to improve and facilitate the entire sample preparation process or integrate sample preparation and fractionation have been reported to reduce time, increase throughput, and improve reproducibility. In this review, we have outlined the current methods used for sample preparation in proteomics, including on-membrane digestion, bead-based digestion, immobilized enzymatic digestion, and suspension trapping. Additionally, we have summarized and discussed current devices and methods for integrating different steps of sample preparation and peptide fractionation.

Methods to improve quantitative glycoprotein coverage from bottom-up LC-MS data

Advances in mass spectrometry instrumentation, methods development, and bioinformatics have greatly improved the ease and accuracy of site-specific, quantitative glycoproteomics analysis. Data-dependent acquisition is the most popular method for identification and quantification of glycopeptides; however, complete coverage of glycosylation site glycoforms remains elusive with this method. Targeted acquisition methods improve the precision and accuracy of quantification, but at the cost of throughput and discoverability. Data-independent acquisition (DIA) holds great promise for more complete and highly quantitative site-specific glycoproteomics analysis, while maintaining the ability to discover novel glycopeptides without prior knowledge. We review additional features that can be used to increase selectivity and coverage to the DIA workflow: retention time modeling, which would simplify the interpretation of complex tandem mass spectra, and ion mobility separation, which would maximize the sampling of all precursors at a giving chromatographic retention time. The instrumentation and bioinformatics to incorporate these features into glycoproteomics analysis exist. These improvements in quantitative, site-specific analysis will enable researchers to assess glycosylation similarity in related biological systems, answering new questions about the interplay between glycosylation state and biological function.

Bifunctional super-hydrophilic mesoporous nanocomposite: a novel nanoprobe for investigation of glycosylation and phosphorylation in Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease. Abnormal glycosylation and phosphorylation modification in AD may be closely related to its pathology. It is of substantial practical significance to simultaneously investigate the roles of phosphorylation and glycosylation in AD. In this work, a bifunctional super-hydrophilic mesoporous nanocomposite (denoted mTiO₂@AuCG) was prepared, which combined hydrophilic interaction chromatography (HILIC) and metal oxide affinity chromatography (MOAC) enrichment strategies to enrich phosphopeptides and glycopeptides, respectively or simultaneously. The mTiO₂@AuCG exhibited excellent performance on the high-efficiency enrichment of glycopeptides (selectivity, 5000:1 molar ratios of BSA/HRP; sensitivity, 0.1 fmol HRP; satisfactory recovery rate; loading capacity, 200 mg/g) and phosphopeptides (selectivity, 1000:1 molar ratios of BSA/β-casein; sensitivity, 0.2 fmol β-casein; satisfactory recovery rate; loading capacity, 200 mg/g). Using these advantages, after single-step enrichment of mTiO₂@AuCG, a total of 209 glycopeptides related to 93 glycoproteins, and 17 phosphopeptides related to 13 phosphoproteins were detected from normal human serum. By contrast, 167 glycopeptides related to 88 glycoproteins, and 14 phosphopeptides related to 12 phosphoproteins were found in AD serum.

A New Strategy for High-Efficient Tandem Enrichment and Simultaneous Profiling of N-Glycopeptides and Phosphopeptides in Lung Cancer Tissue

N-glycosylation and phosphorylation, two common posttranslational modifications, play important roles in various biological processes and are extensively studied for biomarker and drug target screening. Because of their low abundance, enrichment of N-glycopeptides and phosphopeptides prior to LC–MS/MS analysis is essential. However, simultaneous characterization of these two types of posttranslational modifications in complex biological samples is still challenging, especially for tiny amount of samples obtained in tissue biopsy. Here, we introduced a new strategy for the highly efficient tandem enrichment of N-glycopeptides and phosphopeptides using HILIC and TiO₂ microparticles. The N-glycopeptides and phosphosites obtained by tandem enrichment were 21%–377% and 22%–263% higher than those obtained by enriching the two PTM peptides separately, respectively, using 160–20 μg tryptic digested peptides as the starting material. Under the optimized conditions, 2798 N-glycopeptides from 434 N-glycoproteins and 5130 phosphosites from 1986 phosphoproteins were confidently identified from three technical replicates of HeLa cells by mass spectrometry analysis. Application of this tandem enrichment strategy in a lung cancer study led to simultaneous characterization of the two PTM peptides and discovery of hundreds of differentially expressed N-glycosylated and phosphorylated proteins between cancer and normal tissues, demonstrating the high sensitivity of this strategy for investigation of dysregulated PTMs using very limited clinical samples.

Mass Spectrometry-Based Techniques to Elucidate the Sugar Code

Cells encode information in the sequence of biopolymers, such as nucleic acids, proteins, and glycans. Although glycans are essential to all living organisms, surprisingly little is known about the "sugar code" and the biological roles of these molecules. The reason glycobiology lags behind its counterparts dealing with nucleic acids and proteins lies in the complexity of carbohydrate structures, which renders their analysis extremely challenging. Building blocks that may differ only in the configuration of a single stereocenter, combined with the vast possibilities to connect monosaccharide units, lead to an immense variety of isomers, which poses a formidable challenge to conventional mass spectrometry. In recent years, however, a combination of innovative ion activation methods, commercialization of ion mobility-mass spectrometry, progress in gas-phase ion spectroscopy, and advances in computational chemistry have led to a revolution in mass spectrometry-based glycan analysis. The present review focuses on the above techniques that expanded the traditional glycomics toolkit and provided spectacular insight into the structure of these fascinating biomolecules. To emphasize the specific challenges associated with them, major classes of mammalian glycans are discussed in separate sections. By doing so, we aim to put the spotlight on the most important element of glycobiology: the glycans themselves.

Maximizing Depth of PTM Coverage: Generating Robust MS Datasets for Computational Prediction Modeling

Post-translational modifications (PTMs) regulate complex biological processes through the modulation of protein activity, stability, and localization. Insights into the specific modification type and localization within a protein sequence can help ascertain functional significance. Computational models are increasingly demonstrated to offer a low-cost, high-throughput method for comprehensive PTM predictions. Algorithms are optimized using existing experimental PTM data, thus accurate prediction performance relies on the creation of robust datasets. Herein, advancements in mass spectrometry-based proteomics technologies to maximize PTM coverage are reviewed. Further, requisite experimental validation approaches for PTM predictions are explored to ensure that follow-up mechanistic studies are focused on accurate modification sites.

A novel hydrophilic hydrogel with a 3D network structure for the highly efficient enrichment of N-glycopeptides

A novel super-hydrophilic hydrogel (ZIF-8/SAP) was first proposed and facilely fabricated to capture N-glycopeptides from complex biological samples with excellent selectivity and sensitivity.

IgG N-glycans

Glycosylation, one of the most common post-translational modifications in mammalian cells, impacts many biological processes such as cell adhesion, proliferation and differentiation. As the most abundant glycoprotein in human serum, immunoglobulin G (IgG) plays a vital role in immune response and protection. There is a growing body of evidence suggests that IgG structure and function are modulated by attached glycans, especially N-glycans, and aberrant glycosylation is associated with disease states. In this chapter, we review IgG glycan repertoire and function, strategies for profiling IgG N-glycome and recent studies. Mass spectrometry (MS) based techniques are the most powerful tools for profiling IgG glycome. IgG glycans can be divided into high-mannose, biantennary complex and hybrid types, modified with mannosylation, core-fucosylation, galactosylation, bisecting GlcNAcylation, or sialylation. Glycosylation of IgG affects antibody half-life and their affinity and avidity for antigens, regulates crystallizable fragment (Fc) structure and Fcγ receptor signaling, as well as antibody effector function. Because of their critical roles, IgG N-glycans appear to be promising biomarkers for various disease states. Specific IgG glycosylation can convert a pro-inflammatory response to an anti-inflammatory activity. Accordingly, IgG glycoengineering provides a powerful approach to potentially develop effective drugs and treat disease. Based on the understanding of the functional role of IgG glycans, the development of vaccines with enhanced capacity and long-term protection are possible in the near future.

Recent Advances in Lectin-Based Affinity Sorbents for Protein Glycosylation Studies

Glycosylation is one of the most significant post-translational modifications occurring to proteins, since it affects some of their basic properties, such as their half-life or biological activity. The developments in analytical methodologies has greatly contributed to a more comprehensive understanding of the quantitative and qualitative characteristics of the glycosylation state of proteins. Despite those advances, the difficulty of a full characterization of glycosylation still remains, mainly due to the complexity of the glycoprotein and/or glycopeptide mixture especially when they are present in complex biological samples. For this reason, various techniques that allow a prior selective enrichment of exclusively glycosylated proteins or glycopeptides have been developed in the past and are coupled either on- or off- line with separation and detection methods. One of the most commonly implemented enrichment methods includes the use of lectin proteins immobilized on various solid supports. Lectins are a group of different, naturally occurring proteins that share a common characteristic, which concerns their affinity for specific sugar moieties of glycoproteins. This review presents the different formats and conditions for the use of lectins in affinity chromatography and in solid phase extraction, including their use in dispersive mode, along with the recent progress made on either commercial or home-made lectin-based affinity sorbents, which can lead to a fast and automated glycosylation analysis.

Plasma membrane N-glycoproteome analysis of wheat seedling leaves under drought stress

Protein glycosylation is one of the ubiquitous post-translational modifications in eukaryotic cells, which play important roles in plant growth and adverse response. In this study, we performed the first comprehensive wheat plasma membrane N-glycoproteome analysis under drought stress via glycopeptide HILIC enrichment and LC-MS/MS identification. In total, 414 glycosylated sites corresponding to 407 glycopeptides and 312 unique glycoproteins were identified, of which 173 plasma membrane glycoproteins with 215 N-glycosylation sites were significantly regulated by drought stress. Functional enrichment analysis reveals that the significantly regulated N-glycosylation proteins were particularly related to protein kinase activity involved in the reception and transduction of extracellular signal and plant cell wall remolding. The motifs and sequence structures analysis showed that the significantly regulated N-glycosylation sites were concentrated within [NxT] motif, and 79.5% of them were located on the random coil that is always on the protein surface and flexible regions, which could facilitate protein glycosylated modification and enhance protein structural stability via reducing protein flexibility. PNGase F enzyme digestion and glycosylation site mutation further indicated that N-glycosylated modification could increase protein stability. Therefore, N-glycosylated modification is involved in plant adaptation to drought stress by improving the stability of cell wall remodeling related plasma membrane proteins.

Material-assisted mass spectrometric analysis of low molecular weight compounds for biomedical applications

Low molecular weight compounds play an important role in encoding the current physiological state of an individual. Laser desorption/ionization mass spectrometry (LDI MS) offers high sensitivity with low cost for molecular detection, but it is not able to cover small molecules due to the drawbacks of the conventional matrix. Advanced materials are better alternatives, showing little background interference and high LDI efficiency. Herein, we first classify the current materials with a summary of compositions and structures. Matrix preparation protocols are then reviewed, to enhance the selectivity and reproducibility of MS data better. Finally, we highlight the biomedical applications of material-assisted LDI MS, at the tissue, bio-fluid, and cellular levels. We foresee that the advanced materials will bring far-reaching implications in LDI MS towards real-case applications, especially in clinical settings.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth 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 2016. 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. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Differential Glycosite Profiling-A Versatile Method to Compare Membrane Glycoproteomes

Glycosylation is the most prevalent and varied form of post-translational protein modifications. Protein glycosylation regulates multiple cellular functions, including protein folding, cell adhesion, molecular trafficking and clearance, receptor activation, signal transduction, and endocytosis. In particular, membrane proteins are frequently highly glycosylated, which is both linked to physiological processes and of high relevance in various disease mechanisms. The cellular glycome is increasingly considered to be a therapeutic target. Here we describe a new strategy to compare membrane glycoproteomes, thereby identifying proteins with altered glycan structures and the respective glycosites. The workflow started with an optimized procedure for the digestion of membrane proteins followed by the lectin-based isolation of glycopeptides. Since alterations in the glycan part of a glycopeptide cause mass alterations, analytical size exclusion chromatography was applied to detect these mass shifts. N-glycosidase treatment combined with nanoUPLC-coupled mass spectrometry identified the altered glycoproteins and respective glycosites. The methodology was established using the colon cancer cell line CX1, which was treated with 2-deoxy-glucose-a modulator of N-glycosylation. The described methodology is not restricted to cell culture, as it can also be adapted to tissue samples or body fluids. Altogether, it is a useful module in various experimental settings that target glycan functions.

Facile synthesis of bifunctional polymer monolithic column for tunable and specific capture of glycoproteins and phosphoproteins

Efficiently tunable capture of the glycosylated/phosphorylated proteins is critical to meet the need of in-depth glycoproteome and phosphoproteome studies. Reported here is a new bifunctional polymer monolithic column by introducing benzeneboronic acid and phosphonic acid onto monolithic column (denoted as poly (EDMA-co-VPBA-co-VPA) monolith) for tunable and specific enrichment of glycoproteins and phosphoproteins via switching different mobile phases. Based on boronate affinity and immobilized metal affinity, the as-prepared poly (EDMA-co-VPBA-co-VPA) monolith exhibited superior performance in selective separation of small molecules and biomacromolecules containing cis-diol/phosphate groups or not. And the frontal chromatography analysis showed that the binding capacity of the poly (EDMA-co-VPBA-co-VPA) monolith towards horseradish peroxidase (HRP, glycoprotein) or β-casein (phosphoprotein) is four-fold higher than that of bovine serum albumin (BSA, non-glycosylated/phosphorylated protein). Furthermore, combined with mass spectrometry identification, the successful application in specific enrichment of glycopeptides/phosphopeptides from tryptic digests of HRP/β-casein and direct capture of low abundant endogenous phosphopeptides from human serum proved great practicability in complex samples. This study provides a novel insight for fabricating the monolithic columns with multifunctionalization to facilitate further post-translational modification (PTM)-proteomics development.

A Pragmatic Guide to Enrichment Strategies for Mass Spectrometry-Based Glycoproteomics

Glycosylation is a prevalent, yet heterogeneous modification with a broad range of implications in molecular biology. This heterogeneity precludes enrichment strategies that can be universally beneficial for all glycan classes. Thus, choice of enrichment strategy has profound implications on experimental outcomes. Here we review common enrichment strategies used in modern mass spectrometry-based glycoproteomic experiments, including lectins and other affinity chromatographies, hydrophilic interaction chromatography and its derivatives, porous graphitic carbon, reversible and irreversible chemical coupling strategies, and chemical biology tools that often leverage bioorthogonal handles. Interest in glycoproteomics continues to surge as mass spectrometry instrumentation and software improve, so this review aims to help equip researchers with the necessary information to choose appropriate enrichment strategies that best complement these efforts.

Glycoproteomic Analysis Reveals Aberrant Expression of Complement C9 and Fibronectin in the Plasma of Patients with Colorectal Cancer

Colorectal cancer (CRC) is a major cause of cancer mortality. Currently used CRC biomarkers provide insufficient sensitivity and specificity; therefore, novel biomarkers are needed to improve the CRC detection. Label-free quantitative proteomics were used to identify and compare glycoproteins, enriched by wheat germ agglutinin, from plasma of CRC patients and age-matched healthy controls. Among 189 identified glycoproteins, the levels of 7 and 15 glycoproteins were significantly altered in the non-metastatic and metastatic CRC groups, respectively. Protein-protein interaction analysis revealed that they were predominantly involved in immune responses, complement pathways, wound healing and coagulation. Of these, the levels of complement C9 (C9) was increased and fibronectin (FN1) was decreased in both CRC states in comparison to those of the healthy controls. Moreover, their levels detected by immunoblotting were validated in another independent cohort and the results were consistent with in the study cohort. Combination of CEA, a commercial CRC biomarker, with C9 and FN1 showed better diagnostic performance. Interestingly, predominant glycoforms associated with acetylneuraminic acid were obviously detected in alpha-2 macroglobulin, haptoglobin, alpha-1-acid glycoprotein 1, and complement C4-A of CRC patient groups. This glycoproteomic approach provides invaluable information of plasma proteome profiles of CRC patients and identification of CRC biomarker candidates.

Proteomics approaches to understand cell biology and virulence of Entamoeba histolytica protozoan parasite

Entamoeba histolytica is the primitive eukaryotic parasite responsible of human amoebiasis, a disease characterized by bloody intestinal diarrhea and invasive extraintestinal illness. The knowledge of the complete genome sequence of virulent E. histolytica and related non-pathogenic species allowed the development of novel genome-wide methodological approaches including protein expression profiling and cellular proteomics in the so called post-genomic era. Proteomics studies have greatly increased our understanding of the cell biology of this ancient parasite. This review summarizes the current works concerning proteomics studies on cell biology, life cycle, virulence and pathogenesis, novel therapies, and protein expression regulation mechanisms in E. histolytica parasite. Also, we discuss the use of proteomics data for the development of novel therapies, the identification of potential disease biomarkers and differential diagnosis between species. SIGNIFICANCE: Entamoeba histolytica is the unicellular protozoan parasite responsible of human amoebiasis, a serious disease with worldwide distribution characterized by bloody intestinal diarrhea and invasive extraintestinal illness including peritonitis and liver, pulmonary and brain abscesses. The post-genomic era allowed the development of proteomic studies including protein expression profiling and cellular proteomics. These proteomics studies have greatly increased our understanding on cell biology, life cycle (cyst-trophozoite conversion), virulence, pathogenesis, novel therapies, and protein expression regulation mechanisms in E. histolytica. Importantly, proteomics has revealed the identity of proteins related to novel therapies, and the identification of potential disease biomarkers and proteins with use in diagnosis between species. Hopefully in the coming years, and through the use of more sophisticated omics tools, including deep proteomics, a more complete set of proteins involved in the aforementioned cellular processes can be obtained to understand the biology of this ancient eukaryote.

Isomeric Separation of N-Glycopeptides Derived from Glycoproteins by Porous Graphitic Carbon (PGC) LC-MS/MS

Protein glycosylation is involved in many biological processes and physiological functions. Despite the recent advances in LC-MS/MS methodologies, the profiling of site-specific glycosylation is one of the major analytical challenges of glycoprotein analysis. Herein, we report that the separation of glycopeptide isomers on porous graphitic carbon (PGC)-LC was significantly improved by elevating the separation temperature under basic mobile phases. These findings permitted the isomeric separation of glycopeptides resulting from highly specific enzymatic digestions. The selectivity for different glycan types was studied using bovine fetuin, asialofetuin, IgG, ribonuclease B, and alpha-1 acid glycoprotein (AGP) by PGC-LC-MS. Comprehensive structural isomeric separation of glycopeptides was observed by high-resolution MS and confirmed by MS/MS. The specific structures of the glycopeptide isomers were identified and confirmed through exoglycosidase digestions. Glycosylation analysis of human AGP revealed the potential use of PGC-LC-MS for extensive glycoprotein analysis for biomarker discovery. This newly developed separation technique was shown as a reproducible and useful analytical method to study site-specific isomeric glycosylation.

N-Glycosylation of IgG and IgG-Like Recombinant Therapeutic Proteins: Why Is It Important and How Can We Control It?

Regulatory bodies worldwide consider N-glycosylation to be a critical quality attribute for immunoglobulin G (IgG) and IgG-like therapeutics. This consideration is due to the importance of posttranslational modifications in determining the efficacy, safety, and pharmacokinetic properties of biologics. Given its critical role in protein therapeutic production, we review N-glycosylation beginning with an overview of the myriad interactions of N-glycans with other biological factors. We examine the mechanism and drivers for N-glycosylation during biotherapeutic production and the several competing factors that impact glycan formation, including the abundance of precursor nucleotide sugars, transporters, glycosidases, glycosyltransferases, and process conditions. We explore the role of these factors with a focus on the analytical approaches used to characterize glycosylation and associated processes, followed by the current state of advanced glycosylation modeling techniques. This combination of disciplines allows for a deeper understanding of N-glycosylation and will lead to more rational glycan control.

Advances in extracellular vesicles analysis

Extracellular vesicles (EVs) play an important role in intercellular communication in normal cellular process and pathological conditions by facilitating the transport of cellular content from one cell to another. EVs as conveyors of various biological molecules with their ability to redirect effects on a target cell physiological function in cell type-specific manner makes EVs an excellent candidate for drug delivery vehicle in disease therapy. Moreover, unique characteristics and contents of EVs which differ depends on cellular origin and physiological state make them a valuable source of diagnostic biomarker. Herein, we review the current progress in extracellular vesicle (EV) analysis, its transition from biomedical research to advancing therapy, and recent pioneered approaches to characterize and quantify EVs' subclasses with an emphasis on the integration of advanced technologies for both qualitative and quantitative analysis of EVs in different clinical tissue/body fluid samples.

Mass spectrometry combined with affinity probes for the identification of CP4 EPSPS in genetically modified soybeans

Sample preparation methods used for genetically modified organisms (GMOs) analysis are often time consuming, require extensive manual manipulation, and result in limited amounts of purified protein, which may complicate the detection of low-abundance GM protein. A robust sample pretreatment method prior to mass spectrometry (MS) detection of the transgenic protein (5-enolpyruvylshikimate-3-phosphate synthase [CP4 EPSPS]) present in Roundup Ready soya is investigated. Liquid chromatography-multiple reaction monitoring tandem MS (nano LC-MS/MS-MRM) was used for the detection and quantification of CP4 EPSPS. Gold nanoparticles (AuNPs) and concanavalin A (Con A)-immobilized Sepharose 4B were used as selective probes for the separation of the major storage proteins in soybeans. AuNPs that enable the capture of cysteine-containing proteins were used to reduce the complexity of the crude extract of GM soya. Con A-sepharose was used for the affinity capture of β-conglycinin and other glycoproteins of soya prior to enzymatic digestion. The methods enabled the detection of unique peptides of CP4 EPSPS at a level as low as 0.5% of GM soya in MRM mode. Stable-isotope dimethyl labeling was further applied to the quantification of GM soya. Both probes exhibited high selectivity and efficiency for the affinity capture of storage proteins, leading to the quantitative detection at 0.5% GM soya, which is a level below the current European Union's threshold for food labeling. The square correlation coefficients were greater than 0.99. The approach for sample preparation is very simple without the need for time-consuming protein prefractionation or separation procedures and thus presents a significant improvement over existing methods for the analysis of the GM soya protein.

A spherical covalent-organic framework for enhancing laser desorption/ionization mass spectrometry for small molecule detection

A spherical vinyl-functionalized covalent-organic framework (COF-V) was prepared at room temperature by a facile method and applied as a novel substrate for surface-enhanced laser desorption/ionization mass spectrometry (SELDI-MS).

Enrichments of post-translational modifications in proteomic studies

More than 300 different protein post-translational modifications are currently known, but only a few have been extensively investigated because modified proteoforms are commonly present in sub-stoichiometry amount. For this reason, improvement of specific enrichment techniques is particularly useful for the proteomic characterization of post-translationally modified proteins. Enrichment proteomic strategies could help the researcher in the challenging issue to decipher the complex molecular cross-talk existing between the different factors influencing the cellular pathways. In this review the state of art of the platforms applied for the enrichment of specific and most common post-translational modifications, such as glycosylation and glycation, phosphorylation, sulfation, redox modifications (i.e. sulfydration and nitrosylation), methylation, acetylation, and ubiquitinylation, are described. Enrichments strategies applied to characterize less studied post-translational modifications are also briefly discussed.

Isolation and characterization of glycosylated neuropeptides

Glycosylation is one of the most ubiquitous and complex post-translational modifications (PTMs). It plays pivotal roles in various biological processes. Studies at the glycopeptide level are typically considered as a downstream work resulting from enzymatic digested glycoproteins. Less attention has been focused on glycosylated endogenous signaling peptides due to their low abundance, structural heterogeneity and the lack of enabling analytical tools. Here, protocols are presented to isolate and characterize glycosylated neuropeptides utilizing nanoflow liquid chromatography coupled with mass spectrometry (LC-MS). We first demonstrate how to extract neuropeptides from raw tissues and perform further separation/cleanup before MS analysis. Then we describe hybrid MS methods for glycosylated neuropeptide profiling and site-specific analysis. We also include recommendations for data analysis to identify glycosylated neuropeptides in crustaceans where a complete neuropeptide database is still lacking. Other strategies and future directions are discussed to provide readers with alternative approaches and further unravel biological complexity rendered by glycosylation.

Global and site-specific analysis of protein glycosylation in complex biological systems with Mass Spectrometry

Protein glycosylation is ubiquitous in biological systems and plays essential roles in many cellular events. Global and site-specific analysis of glycoproteins in complex biological samples can advance our understanding of glycoprotein functions and cellular activities. However, it is extraordinarily challenging because of the low abundance of many glycoproteins and the heterogeneity of glycan structures. The emergence of mass spectrometry (MS)-based proteomics has provided us an excellent opportunity to comprehensively study proteins and their modifications, including glycosylation. In this review, we first summarize major methods for glycopeptide/glycoprotein enrichment, followed by the chemical and enzymatic methods to generate a mass tag for glycosylation site identification. We next discuss the systematic and quantitative analysis of glycoprotein dynamics. Reversible protein glycosylation is dynamic, and systematic study of glycoprotein dynamics helps us gain insight into glycoprotein functions. The last part of this review focuses on the applications of MS-based proteomics to study glycoproteins in different biological systems, including yeasts, plants, mice, human cells, and clinical samples. Intact glycopeptide analysis is also included in this section. Because of the importance of glycoproteins in complex biological systems, the field of glycoproteomics will continue to grow in the next decade. Innovative and effective MS-based methods will exponentially advance glycoscience, and enable us to identify glycoproteins as effective biomarkers for disease detection and drug targets for disease treatment. © 2019 Wiley Periodicals, Inc. Mass Spec Rev 9999: XX-XX, 2019.

Comparative Glycopeptide Analysis for Protein Glycosylation by Liquid Chromatography and Tandem Mass Spectrometry: Variation in Glycosylation Patterns of Site-Directed Mutagenized Glycoprotein

Glycosylation is one of the most important posttranslational modifications for proteins, including therapeutic antibodies, and greatly influences protein physiochemical properties. In this study, glycopeptide mapping of a reference and biosimilar recombinant antibodies (rAbs) was performed using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) and an automated Glycoproteome Analyzer (GPA) algorithm. The tandem mass analyses for the reference and biosimilar samples indicate that this approach proves to be highly efficient in reproducing consistent analytical results and discovering the implications of different rAb production methods on glycosylation patterns. Furthermore, the comparative analysis of a mutagenized rAb glycoprotein proved that a single amino acid mutation in the Fc portion of the antibody molecule caused increased variations in glycosylation patterns. These variations were also detected by the mass spectrometry method efficiently. This mapping method, focusing on precise glycopeptide identification and comparison for the identified glycoforms, can be useful in differentiating aberrant glycosylation in biosimilar rAb products.

Mass Spectrometry Approaches to Glycomic and Glycoproteomic Analyses

Glycomic and glycoproteomic analyses involve the characterization of oligosaccharides (glycans) conjugated to proteins. Glycans are produced through a complicated nontemplate driven process involving the competition of enzymes that extend the nascent chain. The large diversity of structures, the variations in polarity of the individual saccharide residues, and the poor ionization efficiencies of glycans all conspire to make the analysis arguably much more difficult than any other biopolymer. Furthermore, the large number of glycoforms associated with a specific protein site makes it more difficult to characterize than any post-translational modification. Nonetheless, there have been significant progress, and advanced separation and mass spectrometry methods have been at its center and the main reason for the progress. While glycomic and glycoproteomic analyses are still typically available only through highly specialized laboratories, new software and workflow is making it more accessible. This review focuses on the role of mass spectrometry and separation methods in advancing glycomic and glycoproteomic analyses. It describes the current state of the field and progress toward making it more available to the larger scientific community.

Characterizing bacterial glycoproteins with LC-MS

INTRODUCTION

Though eukaryotic glycoproteins have been studied since their discovery in the 1930s, the first bacterial glycoprotein was not identified until the 1970s. As a result, their role in bacterial pathogenesis is still not well understood and they remain an understudied component of bacterial virulence. In recent years, mass spectrometry has emerged as a leading technology for the study of bacterial glycoproteins, largely due to its sensitivity and versatility. Areas covered: Identification and comprehensive characterization of bacterial glycoproteins usually requires multiple complementary mass spectrometry approaches, including intact protein analysis, top-down analysis, and bottom-up methods used in combination with specialized liquid chromatography. This review provides an overview of liquid chromatography separation technologies, as well as current and emerging mass spectrometry approaches used specifically for bacterial glycoprotein identification and characterization. Expert commentary: Bacterial glycoproteins may have significant clinical utility as a result of their unique structures and exposure on the surface of the cells. Better understanding of these glycoconjugates is an essential first step towards that goal. These often unique structures, and by extension the key enzymes involved in their synthesis, represent promising targets for novel antimicrobials, while unique carbohydrate structures may be used as antigens in vaccines or as biomarkers.

Influence of different sample preparation strategies on the proteomic identification of stress biomarkers in porcine saliva

Background

The influence of two different sample treatments comprising the enrichment of glycoproteins by boronic acid and dynamic range compression by hexapeptide libraries, on the detection of stress markers in saliva of pigs was evaluated in this study. For this purpose, saliva samples collected before and after the application of an acute stress model consisting of nasal restraining in pigs were processed without any treatment and with the two different treatments mentioned above. Protein separation by two-dimensional gel electrophoresis (2-DE) followed by identification of proteins using MALDI-TOF/TOF mass spectrometry (MS) was used as proteomic technique.

Results

The application of each of the two different sample treatment protocols allowed the identification of unique proteins that could be potential salivary acute stress markers in pigs: lipocalin 1, protein S100-A8 and immunoglobulin M by enrichment of glycoproteins; protein S100-A9, double headed protease inhibitor submandibular gland, and haemoglobin by dynamic range compression; and protein S100-A12 by both protocols. Salivary lipocalin, prolactin inducible protein, light chain of immunoglobulins, adenosine deaminase and carbonic anhydrase VI were identified as potential markers in untreated saliva as well as one of the other treatments.

Conclusion

The use of different procedures allowed the detection of different potential stress markers. Although from a practical point of view, the use of saliva without further treatment as well as the enrichment of glycoproteins are less expensive and easy to do procedures.

The sweet spot for biologics: recent advances in characterization of biotherapeutic glycoproteins

INTRODUCTION

Glycosylation is recognized as a Critical Quality Attribute for therapeutic glycoproteins such as monoclonal antibodies, fusion proteins and therapeutic replacement enzymes. Hence, efficient and quantitative glycan analysis techniques have been increasingly important for their discovery, development and quality control. The aim of this review is to highlight relevant and recent advances in analytical technologies for characterization of biotherapeutic glycoproteins. Areas covered: The review gives an overview of the glycosylation trends of biotherapeutics approved in 2016 and 2017 by FDA. It describes current and novel analytical technologies for characterization of therapeutic glycoproteins and is explored in the context of released glycan, glycopeptide or intact glycoprotein analysis. Ultra performance liquid chromatography, mass spectrometry and capillary electrophoresis technologies are explored in this context. Expert commentary: There is a need for the biopharmaceutical industry to incorporate novel state of the art analytical technologies into existing and new therapeutic glycoprotein workflows for safer and more efficient biotherapeutics and for the improvement of future biotherapeutic design. Additionally, at present, there is no 'gold-standard' approach to address all the regulatory requirements and as such this will involve the use of orthogonal glycoanalytical technologies with a view to gain diagnostic information about the therapeutic glycoprotein.

A new panel of pancreatic cancer biomarkers discovered using a mass spectrometry-based pipeline

Background:

Pancreatic carcinoma (PC) is an aggressive malignancy that lacks strategies for early detection. This study aimed to develop a coherent, high-throughput and non-discriminatory pipeline for the novel clinical biomarker discovery of PC.

Methods:

We combined mass spectrometry (MS)-intensive methods such as isobaric tags for relative and absolute quantitation with two-dimensional liquid chromatography-tandem mass spectrometry (iTRAQ-2DLC-MS/MS), 1D-targeted LC-MS/MS, prime MRM (P-MRM) and stable isotope dilution-based MRM (SID-MRM) to analyse serum samples from healthy people (normal control, NC), patients with benign diseases (BD) and PC patients to identify novel biomarkers of PC.

Results:

On the basis of the newly developed pipeline, we identified >1000 proteins, verified 142 differentially expressed proteins and finally targeted four proteins for absolute quantitation in 100 serum samples. The novel biomarker panel of apolipoprotein E (APOE), inter-alpha-trypsin inhibitor heavy chain H3 (ITIH3), apolipoprotein A-I (APOA1), apolipoprotein L1 (APOL1), combining with CA19-9, statistically-significantly improved the sensitivity (95%) and specificity (94.1%), outperforming CA19-9 alone, for the diagnosis of PC.

Conclusions:

We developed a highly efficient pipeline for biomarker discovery, verification and validation, with each step systematically informing the next. A panel of proteins that might be clinically relevant biomarkers for PC was found.

Site-Specific Fucosylation Analysis Identifying Glycoproteins Associated with Aggressive Prostate Cancer Cell Lines Using Tandem Affinity Enrichments of Intact Glycopeptides Followed by Mass Spectrometry

Fucosylation (Fuc) of glycoproteins plays an important role in regulating protein function and has been associated with the development of several cancer types including prostate cancer (Pca). Therefore, the research of Fuc glycoproteins has attracted increasing attention recently in the analytical field. Herein, a strategy based on lectin affinity enrichments of intact glycopeptides followed by mass spectrometry has been established to evaluate the specificities of various Fuc-binding lectins for glycosite-specific Fuc analysis of nonaggressive (NAG) and aggressive (AG) Pca cell lines. The enrichment specificities of Fuc glycopeptides using lectins (LCA, PSA, AAL, LTL, UEA I, and AOL) and MAX extraction cartridges alone, or in tandem, were evaluated. Our results showed that the use of lectin enrichment significantly increased the ratio of fucosylated glycopeptides to total glycopeptides compared to MAX enrichment. Furthermore, tandem use of lectin followed by MAX increased the number of identifications of Fuc glycopeptides compared to using lectin enrichment alone. LCA, PSA, and AOL showed stronger binding capacity than AAL, LTL, and UEA I. Also, LCA and PSA bound specifically to core Fuc, whereas AOL, AAL, and UEA I showed binding to both core Fuc and branch Fuc. The optimized enrichment method with tandem enrichment of LCA followed by MAX (LCA-MAX) was then applied to examine the Fuc glycoproteomes in two NAG and two AG Pca cell lines. In total, 973 intact Fuc glycopeptides were identified and quantified from 252 Fuc proteins by using the tandem-mass-tags (TMT) labeling and nanoliquid chromatography-mass spectrometry (nanoLC-MS/MS) analysis. Further data analysis revealed that 51 Fuc glycopeptides were overexpressed more than 2-fold in AG cell lines compared to NAG cells. The analysis of protein core fucosylation has great potential for aiding our understanding of invasive activity of AG Pca and may lead to the development of diagnostic approaches for AG Pca.

Glycoconjugates from extracellular vesicles: Structures, functions and emerging potential as cancer biomarkers

Extracellular vesicles (EVs) are released by virtually all cells, carry cellular molecules to the extracellular environment, and may interact with other cells. They are found in body fluids, therefore, constituting useful target sources for the identification of disease biomarkers, for example, in cancer. EVs originate from the plasma membrane or from multivesicular endosomes. They have the same topology as the plasma membrane and are rich in glycoconjugates, displaying specific glycosignatures. Surface glycoconjugates play important roles in EVs biogenesis and in their interaction with other cells. Changes in glycosylation constitute a hallmark of different types of cancer, therefore, the study of glycoconjugates and glycosignatures of EVs appear as promising candidates to identify novel cancer biomarkers and to increase the specificity and sensitivity of the existing clinical biomarkers, many of which are glycosylated.

Mapping the N-linked glycosites of rice (Oryza sativa L.) germinating embryos

Germination is a key event in the angiosperm life cycle. N-glycosylation of proteins is one of the most common post-translational modifications, and has been recognized to be an important regulator of the proteome of the germinating embryo. Here, we report the first N-linked glycosites mapping of rice embryos during germination by using a hydrophilic interaction chromatography (HILIC) glycopeptides enrichment strategy associated with high accuracy mass spectrometry identification. A total of 242 glycosites from 191 unique proteins was discovered. Inspection of the motifs and sequence structures involved suggested that all the glycosites were concentrated within [NxS/T] motif, while 82.3% of them were in a coil structure. N-glycosylation preferentially occurred on proteins with glycoside hydrolase activities, which were significantly enriched in the starch and sucrose metabolism pathway, suggesting that N-glycosylation is involved in embryo germination by regulating carbohydrate metabolism. Notably, protein-protein interaction analysis revealed a network with several Brassinosteroids signaling proteins, including XIAO and other BR-responsive proteins, implying that glycosylation-mediated Brassinosteroids signaling may be a key mechanism regulating rice embryo germination. In summary, this study expanded our knowledge of protein glycosylation in rice, and provided novel insight into the PTM regulation in rice seed germination.

Site-specific monitoring of N-Glycosylation profiles of a CTLA4-Fc-fusion protein from the secretory pathway to the extracellular environment

Glycosylation often plays a key role in the safety and efficacy of therapeutic proteins to patients, thus underlying the need for consistent control of this important post-translational modification during biologics production. In this study, we profiled the site-specific evolution of N-glycans on a CTLA4-Fc-fusion protein, from the intracellular secretory pathway to the conditioned medium (CM) in fed-batch cell culture. For this, we developed an approach that combined sub-cellular fractionation with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. The study revealed that there was a significant amount of heterogeneity in the glycans displayed amongst the three distinct N-glycosylation sites. Furthermore, 54-60% of the intracellular protein was characterized by Man8 and Man9 glycans on day 10, when the cell density peaks, indicative of a significant bottleneck between the endoplasmic reticulum (ER) and the cis-Golgi. At longer culture duration, the accumulation of intracellular protein with bi-antennary-fucosylated GlcNAc-terminated residues identified the formation of another bottleneck in the medial and trans-Golgi compartments, which subsequently led to a decrease in sialylated species in the secreted protein. Glucose deprivation caused a reduction in the Man8 and Man9 glycans in favor of Man5 glycans and bi-antennary-fucosylated GlcNAc-terminated residues in the organellar pool of the Fc-fusion protein. However, transient deprivation of glucose did not lead to major differences in the glycan profile of proteins secreted into the CM. The approach developed here allows us to probe the secretory pathway and sheds light on the site-specific intracellular processing of glycans during fed-batch cell culture, thus serving as an initial step towards their rational control. Biotechnol. Bioeng. 2017;114: 1550-1560. © 2017 Wiley Periodicals, Inc.

Application of Porous Materials to Carbohydrate Chemistry and Glycoscience

There is a growing interest in using a range of porous materials to meet research needs in carbohydrate chemistry and glycoscience in general. Among the applications of porous materials reviewed in this chapter, enrichment of glycans from biological samples prior to separation and analysis by mass spectrometry is a major emphasis. Porous materials offer high surface area, adjustable pore sizes, and tunable surface chemistry for interacting with glycans, by boronate affinity, hydrophilic interactions, molecular imprinting, and polar interactions. Among the materials covered in this review are mesoporous silica and related materials, porous graphitic carbon, mesoporous carbon, porous polymers, and nanoporous gold. In some applications, glycans are enzymatically or chemically released from glycoproteins or glycopeptides, and the porous materials have the advantage of size selectivity admitting only the glycans into the pores and excluding proteins. Immobilization of lectins onto porous materials of suitable pore size allows for the use of lectin-carbohydrate interactions in capture or separation of glycoproteins. Porous material surfaces modified with carbohydrates can be used for the selective capture of lectins. Controlled release of therapeutics from porous materials mediated by glycans has been reported, and so has therapeutic targeting using carbohydrate-modified porous particles. Additional applications of porous materials in glycoscience include their use in the supported synthesis of oligosaccharides and in the development of biosensors for glycans.

Recent advances in mass spectrometric analysis of glycoproteins

Glycosylation is one of the most common posttranslational modifications of proteins that plays essential roles in various biological processes, including protein folding, host-pathogen interaction, immune response, and inflammation and aberrant protein glycosylation is a well-known event in various disease states including cancer. As a result, it is critical to develop rapid and sensitive methods for the analysis of abnormal glycoproteins associated with diseases. Mass spectrometry (MS) in conjunction with different separation methods, such as capillary electrophoresis (CE), ion mobility (IM), and high performance liquid chromatography (HPLC) has become a popular tool for glycoprotein analysis, providing highly informative fragments for structural identification of glycoproteins. This review provides an overview of the developments and accomplishments in the field of glycomics and glycoproteomics reported between 2014 and 2016.

Chemical Glycoproteomics

Chemical tools have accelerated progress in glycoscience, reducing experimental barriers to studying protein glycosylation, the most widespread and complex form of posttranslational modification. For example, chemical glycoproteomics technologies have enabled the identification of specific glycosylation sites and glycan structures that modulate protein function in a number of biological processes. This field is now entering a stage of logarithmic growth, during which chemical innovations combined with mass spectrometry advances could make it possible to fully characterize the human glycoproteome. In this review, we describe the important role that chemical glycoproteomics methods are playing in such efforts. We summarize developments in four key areas: enrichment of glycoproteins and glycopeptides from complex mixtures, emphasizing methods that exploit unique chemical properties of glycans or introduce unnatural functional groups through metabolic labeling and chemoenzymatic tagging; identification of sites of protein glycosylation; targeted glycoproteomics; and functional glycoproteomics, with a focus on probing interactions between glycoproteins and glycan-binding proteins. Our goal with this survey is to provide a foundation on which continued technological advancements can be made to promote further explorations of protein glycosylation.

Combining Click Chemistry-Based Proteomics With Dox-Inducible Gene Expression

Inactivating mutations in single genes can trigger, prevent, promote, or alleviate diseases. Identifying such disease-related genes is a main pillar of medical research. Since proteins play a crucial role in mediating these effects, their impact on the diseased cells' proteome including posttranslational modifications has to be elucidated for a detailed understanding of the role of these genes in the disease process. In complex disorders, like cancer, several genes contribute to the disease process, thereby hampering the assignment of a proteomic change to the corresponding causative gene. To enable comprehensive screening for the impact of inactivation of a gene, e.g., loss of a tumor suppressor in cancer, on the cellular proteome, we present a strategy based on combination of three technologies that is recombinase-mediated cassette exchange, click chemistry, and mass spectrometry. The methodology is exemplified by the analysis of the proteomic changes induced by the loss of a tumor suppressor gene in colorectal cancer cells. To demonstrate the applicability to screen for posttranslational modification changes, we also describe the analysis of protein glycosylation changes caused by the tumor suppressor inactivation. In principle, this strategy can be applied to analyze the effects of any gene of interest on protein expression as well as posttranslational modification by glycosylation. Moreover adaptation of the strategy to an appropriate cell culture model has the potential for application on a broad range of diseases where the disease-promoting mutations have been identified.