Plasma protein N-glycosylation is associated with cardiovascular disease, nephropathy, and retinopathy in type 2 diabetes

IntroductionAlthough associations of total plasma N-glycome (TPNG) with type 2 diabetes have been reported, little is known on the role of TPNG in type 2 diabetes complications, a major cause of type 2 diabetes-related morbidity and mortality. Here, we assessed TPNG in relation to type 2 diabetes complications in subsamples of two Dutch cohorts using mass spectrometry (n=1815 in DiaGene and n=1518 in Hoorn Diabetes Care System).Research design and methodsBlood plasma samples and technical replicates were pipetted into 96-well plates in a randomized manner. Peptide:N-glycosidase F (PNGase F) was used to release N-glycans, whereafter sialic acids were derivatized for stabilization and linkage differentiation. After total area normalization, 68 individual glycan compositions were quantified in total and were used to calculate 45 derived traits which reflect structural features of glycosylation. Associations of glycan features with prevalent and incident microvascular or macrovascular complications were tested in logistic and Cox regression in both independent cohorts and the results were meta-analyzed.ResultsOur results demonstrated similarities between incident and prevalent complications. The strongest association for prevalent cardiovascular disease was a high level of bisection on a group of diantennary glycans (A2FS0B; OR=1.38, p=1.34×10−11), while for prevalent nephropathy the increase in 2,6-sialylation on triantennary glycans was most pronounced (A3E; OR=1.28, p=9.70×10−6). Several other TPNG features, including fucosylation, galactosylation, and sialylation, firmly demonstrated associations with prevalent and incident complications of type 2 diabetes.ConclusionsThese findings may provide a glance on how TPNG patterns change before complications emerge, paving the way for future studies on prediction biomarkers and potentially disease mechanisms.

O-Glycosylation Landscapes of SARS-CoV-2 Spike Proteins

The densely glycosylated spike (S) proteins that are highly exposed on the surface of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) facilitate viral attachment, entry, and membrane fusion. We have previously reported all the 22 N-glycosites and site-specific N-glycans in the S protein protomer. Herein, we report the O-glycosylation landscapes of SARS-CoV-2 S proteins, which were characterized through high-resolution mass spectrometry. Following digestion with trypsin and trypsin/Glu-C, and de-N-glycosylation using PNGase F, we determined the GalNAc-type O-glycosylation pattern of S proteins, including O-glycosites and the six most common O-glycans occupying them, via Byonic identification and manual validation. Finally, 255 intact O-glycopeptides composed of 50 peptides sequences and 43 O-glycosites were discovered by higher energy collision-induced dissociation (HCD), and three O-glycosites were confidently identified by electron transfer/higher energy collision-induced dissociation (EThcD) in the insect cell-expressed S protein. Most glycosites were modified by non-sialylated O-glycans such as HexNAc(1) and HexNAc(1)Hex (1). In contrast, in the human cell-expressed S protein S1 subunit, 407 intact O-glycopeptides composed of 34 peptides sequences and 30 O-glycosites were discovered by HCD, and 11 O-glycosites were unambiguously assigned by EThcD. However, the measurement of O-glycosylation occupancy hasn’t been made. Most glycosites were modified by sialylated O-glycans such as HexNAc(1)Hex (1)NeuAc (1) and HexNAc(1)Hex (1)NeuAc (2). Our results reveal that the SARS-CoV-2 S protein is an O-glycoprotein; the O-glycosites and O-glycan compositions vary with the host cell type. These comprehensive O-glycosylation landscapes of the S protein are expected to provide novel insights into the viral binding mechanism and present a strategy for the development of vaccines and targeted drugs.

Glycans unique to the relapse-prone subset within triple-negative breast cancer as revealed by lectin array-based analysis of surgical specimens

Introduction Molecular and cellular characteristics of the relapse-prone subset within triple-negative breast cancer (TNBC) remain unclear. Aberrant glycosylation is involved in the malignant behavior of cancer cells. In the present study, we aimed to reveal glycan profiles unique to relapsed TNBC patients. Methods Thirty TNBC patients who did not undergo neoadjuvant chemotherapy but postoperative standard adjuvant therapy from 2009 through 2016 at Juntendo Hospital were investigated. TNBC cells were resected from primary breast cancer sections of formalin-fixed surgical specimens using laser-assisted microdissection. The binding intensities of the extracted glycoproteins to 45 lectins were quantified using lectin microarray and compared between relapsed and non-relapsed patients. Immunohistochemical staining with TJA-II lectin in specimen sections was performed. Results Five patients relapsed during the follow-up (range 37–123 months). Lectin microarray analysis revealed that 7 out of 45 lectins showed significant differences in binding intensity between the relapsed and the non-relapsed group. TJA-II, ACA, WFA, and BPL showed stronger binding in the relapsed group. PNGase F treatment of TNBC cell lysates suggested that TJA-II and ACA bind O-glycans. TJA-II staining of tissue sections revealed strong binding to cell surface membranes and to the cytoplasm of TNBC cells, but not to other types of cells. Significantly more TNBC cells were stained in tissue sections from relapsed than non-relapsed patients. Conclusions TNBC cells from relapsed patients showed a unique lectin reactivity, with higher levels of TJA-II (also WFA and BPL) binding than in non-relapsed patients. The results are potentially useful to develop new prognostic and therapeutic tools.

Improving the Study of Protein Glycosylation with New Tools for Glycopeptide Enrichment

High confidence methods are needed for determining the glycosylation profiles of complex biological samples as well as recombinant therapeutic proteins. A common glycan analysis workflow involves liberation of N-glycans from glycoproteins with PNGase F or O-glycans by hydrazinolysis prior to their analysis. This method is limited in that it does not permit determination of glycan attachment sites. Alternative proteomics-based workflows are emerging that utilize site-specific proteolysis to generate peptide mixtures followed by selective enrichment strategies to isolate glycopeptides. Methods designed for the analysis of complex samples can yield a comprehensive snapshot of individual glycans species, the site of attachment of each individual glycan and the identity of the respective protein in many cases. This chapter will highlight advancements in enzymes that digest glycoproteins into distinct fragments and new strategies to enrich specific glycopeptides.

An Ultrafast N-Glycoproteome Analysis Method Using Thermoresponsive Magnetic Fluid-Immobilized Enzymes

N-Glycosylation is one of the most common and important post-translational modification methods, and it plays a vital role in controlling many biological processes. Increasing discovery of abnormal alterations in N-linked glycans associated with many diseases leads to greater demands for rapid and efficient N-glycosylation profiling in large-scale clinical samples. In the workflow of global N-glycosylation analysis, enzymatic digestion is the main rate-limiting step, and it includes both protease digestion and peptide-N4–(N-acetyl-beta-glucosaminyl) asparagine amidase (PNGase) F deglycosylation. Prolonged incubation time is generally required because of the limited digestion efficiency of the conventional in-solution digestion method. Here, we propose novel thermoresponsive magnetic fluid (TMF)-immobilized enzymes (trypsin or PNGase F) for ultrafast and highly efficient proteome digestion and deglycosylation. Unlike other magnetic material-immobilized enzymes, TMF-immobilized enzymes display a unique temperature-triggered magnetic response behavior. At room temperature, a TMF-immobilized enzyme completely dissolves in an aqueous solution and forms a homogeneous system with a protein/peptide sample for efficient digestion but cannot be separated by magnetic force because of its excellent water dispersity. Above its lower critical solution temperature (LCST), thermoflocculation of a TMF-immobilized enzyme allows it to be easily recovered by increasing the temperature and magnetic force. Taking advantage of the unique homogeneous reaction of a TMF-immobilized enzyme, both protein digestion and glycopeptide deglycosylation can be finished within 3 min, and the whole sample processing time can be reduced by more than 20 times. The application of a TMF-immobilized enzyme in large-scale profiling of protein N-glycosylation in urine samples led to the successful identification of 2,197 N-glycopeptides and further demonstrated the potential of this strategy for fast and high-throughput analysis of N-glycoproteome in clinical samples.

The Analysis of Human Serum N-Glycosylation in Patients with Primary and Metastatic Brain Tumors

The identification of patients with different brain tumors is solely built on imaging diagnostics, indicating the need for novel methods to facilitate disease recognition. Glycosylation is a chemical modification of proteins, reportedly altered in several inflammatory and malignant diseases, providing a potential alternative route for disease detection. In this paper, we report the quantitative analysis of serum N-glycosylation of patients diagnosed with primary and metastatic brain tumors. PNGase-F-digested and procainamide-labeled serum glycans were purified by magnetic nanoparticles, followed by quantitative liquid chromatographic analysis. The glycan structures were identified by the combination of single quad mass spectrometric detection and exoglycosidase digestions. Linear discriminant analysis provided a clear separation of different disease groups and healthy controls based on their N-glycome pattern. Altered distribution of biantennary neutral, sialylated but nonfucosylated, and sialylated–fucosylated structures were found to be the most significant changes. Our results demonstrate that serum glycosylation monitoring could improve the detection of malignancy.

Characterizing Coagulation FVII from iPSC-Hepatocytes-like Cells: Setting the Basis for Cell Therapy Development

Introduction To date studies on factor (F)VII and other hepatic vitamin K-dependent coagulation factors have relied on cell lines overexpressing these human genes. Even though these models have provided insight into the biology of these factors, they do not fully illustrate the in vivo situation. Thus, a relevant physiological model that mimics the in vivo processing of FVII in liver cells with potential for therapeutic use is needed. Methods Human induced pluripotent stem cells (hiPSCs) were differentiated into hepatocyte-like cells (iHLCs) using a non-transcription factor based, small molecule approach. Cells were grown in medium with vitamin K to ensure a correct gamma-carboxylation. Cellular FVII mRNA and protein were determined by RT-qPCR and proteomic and Western blot (WB), respectively. Secreted FVII antigen was measured by ELISA and WB and FVII activity was assessed by chromogenic assay and thrombin generation assay (TGA). Post-translational modifications of FVII protein (glycosylation) were studied using digestion with N-glycosylase F (PNGase F) and neuraminidase. Confocal immunofluorescence microscopy was used to assess the cellular expression of FVII and other vitamin K- dependent coagulation factors and inhibitors. Human primary hepatocytes or human plasma pool were used as a control in the assays. Results The resulting iHLCs expressed FVII mRNA in comparable levels to primary hepatocytes and cellular FVII peptides were identified by mass spectrometry studies. iHLCs secreted FVII at levels of around 70% compared to primary hepatocytes with detectable activity around 35% of the FVII activity level from primary hepatocytes. The TGA showed that cell medium from iHLCs when mixed with FVII deficient plasma was able to induce thrombin generation faster than the FVII depleted plasma alone (lagtime 3.2 vs 27.6 s, respectively). PNGase-F treatment showed that FVII secreted by iHLCs was N-glycosylated. Intracellular FVII was detected by WB as a band of approximately 63 kDa, slightly larger than FVII from plasma pool but similar to FVII from primary hepatocytes. Moreover, additional coagulation factors and inhibitors such as FII, FX, protein C and antithrombin were detected both at the mRNA and protein levels in the cells. Conclusions Stem cell-derived iHLCs produce and secrete FVII at physiologically relevant levels. The resulting FVII showed similar post-translational modifications to plasma FVII although some differences in proteolysis could be inferred. This iHLCs-derived FVII is able to initiate the extrinsic coagulation pathway. Our data support that these iHLCs can serve as a highly relevant model to study FVII and other vitamin K-dependent coagulation factors in vitro and constitute an important step towards the development of novel cell-based therapies for both FVII and other vitamin K-dependent coagulation factor deficiencies. Disclosures No relevant conflicts of interest to declare.

Mucin-type O-glycosylation Landscapes of SARS-CoV-2 Spike Proteins

ABSTRACTThe densely glycosylated spike (S) proteins that are highly exposed on the surface of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) facilitate viral attachment, entry, and membrane fusion. We have previously reported all the 22 N-glycosites and site-specific N-glycans in the S protein protomer. Herein, we report the comprehensive and precise site-specific O-glycosylation landscapes of SARS-CoV-2 S proteins, which were characterized using high-resolution mass spectrometry. Following digestion using trypsin and trypsin/Glu-C, and de-N-glycosylation using PNGase F, we determined the mucin-type (GalNAc-type) O-glycosylation pattern of S proteins, including unambiguous O-glycosites and the 6 most common O-glycans occupying them, via Byonic identification and manual validation. Finally, 43 O-glycosites were identified in the insect cell-expressed S protein. Most glycosites were modified by non-sialylated O-glycans such as HexNAc(1) and HexNAc(1)Hex(1). In contrast, 30 O-glycosites were identified in the human cell-expressed S protein S1 subunit. Most glycosites were modified by sialylated O-glycans such as HexNAc(1)Hex(1)NeuAc(1) and HexNAc(1)Hex(1)NeuAc(2). Our results are the first to reveal that the SARS-CoV-2 S protein is a mucin-type glycoprotein; clustered O-glycans often occur in the N- and the C-termini of the S protein, and the O-glycosite and O-glycan compositions vary with the host cell type. These site-specific O-glycosylation landscapes of the SARS-CoV-2 S protein are expected to provide novel insights into the viral binding mechanism and present a strategy for the development of vaccines and targeted drugs.

Evaluation of different PNGase F enzymes in immunoglobulin G and total plasma N-glycans analysis

Glycoproteins, proteins that are co- and posttranslationally modified by sugars (glycans), have significant roles in pathophysiology of many different diseases. One of the main steps in sample preparation for free N-glycan analysis is deglycosylation or glycan removal. The aim of this study was to compare different peptide N-glycosidase F (PNGase F) enzymes (Rapid PNGase F and two recombinant versions) for deglycosylation of total human plasma glycoproteins and different amounts of human immunoglobulin G (IgG). Deglycosylation with different PNGase F enzymes resulted in different IgG and plasma N-glycosylation hydrophilic interaction liquid chromatography ultra-performance liquid chromatography profiles. Additionally, one recombinant version of PNGase F is more efficient in deglycosylation of complex N-glycans compared with Rapid PNGase F and recombinant version of PNGase F from a different manufacturer. In terms of chromatographic peak intensities and coefficient of variation %Area values, all tested versions of PNGase F enzymes were very reproducible and on the similar level when used in optimal conditions. However, care should be taken in terms of which enzyme is used with which protocol, particularly when scaling up.

The consensus Nglyco-X-S/T motif and a previously unknown Nglyco-N -linked glycosylation are necessary for growth and pathogenicity of Phytophthora

Asparagine (Asn, N) -linked glycosylation within the glycosylation motif (Nglyco-X-S/T; X≠P) is a ubiquitously distributed post-translational modification that participates in diverse eukaryotic cellular processes. However, little is known about the characteristic features and roles of N-glycosylation in oomycetes. In this work, it found that 2.5 μg/ml tunicamycin (N-glycosylation inhibitor) completely inhibited Phytophthora sojae growth, suggesting that N-glycosylation is necessary for oomycete development. We conducted a glycoproteomic analysis of P. sojae to identify and map all N-glycosylated proteins and to quantify differentially expressed glycoproteins associated with mycelia, asexual cysts, and sexual oospores. A total of 355 N-glycosylated proteins were found, containing 496 glycosites that likely participate in glycan degradation, carbon metabolism, glycolysis, or other central metabolic pathways. To verify the glycoproteomic results and further examine the function of N-glycosylation in P. sojae, two proteins were selected for PNGase F deglycosylation assays and CRISPR/Cas9-mediated site-directed mutagenesis, including a GPI transamidase protein (GPI16) up-regulated in cysts, with the consensus Nglyco-X-S/T motif at Asn 94, and a heat shock protein 70 (HSP70) up-regulated in cysts and oospores with a previously unknown Nglyco-N motif at Asn 270. We demonstrated that the GPI16 and HSP70 are both N-glycosylated proteins, confirming that the Nglyco-N motif is a target site for asparagine - oligosaccharide N-glycosidic linkage. Glycosite mutations of Asn 94 in the GPI16 led to impaired cyst germination and pathogenicity, while HSP70 mutants exhibited decreased cyst germination and oospore production. This work describes an integrated map of oomycete N-glycoproteomes and advances our understanding of N-glycosylation in oomycetes. Moreover, we confirm that the consensus Nglyco-X-S/T and the Nglyco-N -linked glycosites are both essential for the growth of Phytophthora sojae, indicating that there are multiple N-glycosylation motifs in oomycetes.