Glycan and Protein Analysis of Glycoengineered Bacterial E. coli Vaccines by MALDI-in-Source Decay FT-ICR Mass Spectrometry

Comprehensive characterization of bacterial glycoconjugate vaccines by liquid chromatography - mass spectrometry

Bacterial pathogens can cause a broad range of infections with detrimental effects on health. Vaccine development is essential as multi-drug resistance in bacterial infections is a rising concern. Recombinantly produced proteins carrying O-antigen glycosylation are promising glycoconjugate vaccine candidates to prevent bacterial infections. However, methods for their comprehensive structural characterization are lacking. Here, we present a bottom-up approach for their site-specific characterization, detecting N-glycopeptides by nano reversed-phase liquid chromatography-mass spectrometry (RP-LC-MS). Glycopeptide analyses revealed information on partial site-occupancy and site-specific glycosylation heterogeneity and helped corroborate the polysaccharide structures and their modifications. Bottom-up analysis was complemented by intact glycoprotein analysis using nano RP-LC-MS allowing the fast visualization of the polysaccharide distribution in the intact glycoconjugate. At the glycopeptide level, the model glycoconjugates analyzed showed different repeat unit (RU) distributions that spanned from 1 to 21 RUs attached to each of the different glycosylation sites. Interestingly, the intact glycoprotein analysis displayed a RU distribution ranging from 1 to 28 RUs, showing the predominant species when the different glycopeptide distributions are combined in the intact glycoconjugate. The complete workflow based on LC-MS measurements allows detailed and comprehensive analysis of the glycosylation state of glycoconjugate vaccines.

Direct glycosylation analysis of intact monoclonal antibodies combining ESI MS of glycoforms and MALDI-in source decay MS of glycan fragments

Monoclonal antibody (mAb) glycoengineering has the potential to improve the efficacy of biopharmaceuticals by fine-tuning specific biological properties. Glycosylation analysis is key to monitoring the glycoengineering process. Various mass spectrometry (MS)-based methods are available to characterize mAb glycosylation at different structural levels, but comprehensive analysis is typically time-consuming and costly. Here, we present an approach that combines conventional intact mass measurement of glycoforms by direct infusion ESI-MS with an advanced MALDI-in-source decay FT-ICR MS method for direct analysis of glycans in intact mAbs, without the need for enzymatic release and separation. Using a sodium-doped MALDI matrix, glycans were directly released as ISD fragment ions from the intact mAbs during the ionization process. Measurement of 0,2A fragment signals yielded reproducible glycan profiles that were consistent with conventional methods, yet was achieved with unprecedented speed, providing complementary information to that obtained through intact mass measurement. The methods were applied to standard and glycoengineered trastuzumab and rituximab, allowing rapid glycosylation profiling and structural analysis of glycans by tandem MS of selected ISD fragment ions. This fast approach can facilitate the early-phase development of glycoengineering processes by constraining further in-depth analyses. We envision a broader applicability in studies focused on glycosylation changes in mAbs.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2021-2022

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates is a well-established technique and this review is the 12th update of the original article published in 1999 and brings coverage of the literature to the end of 2022. As with previous review, this review also includes a few papers that describe methods appropriate to analysis by MALDI, such as sample preparation, even though the ionization method is not MALDI. The review follows the same format as previous reviews. It is divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of computer software for structural identification. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other general areas such as medicine, industrial processes, natural products and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. MALDI is still an ideal technique for carbohydrate analysis, particularly in its ability to produce single ions from each analyte and advancements in the technique and range of applications show little sign of diminishing.

MALDI glycotyping of O-antigens from a single colony of gram-negative bacteria

Polypeptide-targeted MALDI-TOF MS for microbial species identification has revolutionized microbiology. However, no practical MALDI-TOF MS identification method for O-antigen polysaccharides, a major indicator for epidemiological classification within a species of gram-negative bacteria, is available. We describe a simple MALDI glycotyping method for O-antigens that simultaneously identifies the molecular mass of the repeating units and the monosaccharide composition of the O-antigen. We analyzed the Escherichia coli O1, O6, and O157-type strains. Conventional species identification based on polypeptide patterns and O-antigen polysaccharide typing can be performed in parallel from a single colony using our MALDI-TOF MS workflow. Moreover, subtyping within the same O-antigen and parallel colony-specific O-antigen determination from mixed strains, including the simultaneous identification of multiple strains-derived O-antigens within selected colony, were performed. In MALDI glycotyping of two Enterobacteriaceae strains, a Citrobacter freundii strain serologically cross-reactive with E. coli O157 gave a MALDI spectral pattern identical to E. coli O157. On the other hand, an Edwardsiella tarda strain with no reported O-antigen cross-reactivity gave a MALDI spectral pattern of unknown O-antigen repeating units. The method described in this study allows the parallel and rapid identification of microbial genera, species, and serotypes of surface polysaccharides using a single MALDI-TOF MS instrument.

Mass Spectrometry Strategies for O-Glycoproteomics

Glycoproteomics has accelerated in recent decades owing to numerous innovations in the analytical workflow. In particular, new mass spectrometry strategies have contributed to inroads in O-glycoproteomics, a field that lags behind N-glycoproteomics due to several unique challenges associated with the complexity of O-glycosylation. This review will focus on progress in sample preparation, enrichment strategies, and MS/MS techniques for the identification and characterization of O-glycoproteins.

rMSIfragment: improving MALDI-MSI lipidomics through automated in-source fragment annotation

Matrix-Assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI-MSI) spatially resolves the chemical composition of tissues. Lipids are of particular interest, as they influence important biological processes in health and disease. However, the identification of lipids in MALDI-MSI remains a challenge due to the lack of chromatographic separation or untargeted tandem mass spectrometry. Recent studies have proposed the use of MALDI in-source fragmentation to infer structural information and aid identification. Here we present rMSIfragment, an open-source R package that exploits known adducts and fragmentation pathways to confidently annotate lipids in MALDI-MSI. The annotations are ranked using a novel score that demonstrates an area under the curve of 0.7 in ROC analyses using HPLC-MS and Target-Decoy validations. rMSIfragment applies to multiple MALDI-MSI sample types and experimental setups. Finally, we demonstrate that overlooking in-source fragments increases the number of incorrect annotations. Annotation workflows should consider in-source fragmentation tools such as rMSIfragment to increase annotation confidence and reduce the number of false positives.

Carriers and Antigens: New Developments in Glycoconjugate Vaccines

Glycoconjugate vaccines have proven their worth in the protection and prevention of infectious diseases. The introduction of the Haemophilus influenzae type b vaccine is the prime example, followed by other glycoconjugate vaccines. Glycoconjugate vaccines consist of two components: the carrier protein and the carbohydrate antigen. Current carrier proteins are tetanus toxoid, diphtheria toxoid, CRM197, Haemophilus protein D and the outer membrane protein complex of serogroup B meningococcus. Carbohydrate antigens have been produced mainly by extraction and purification from the original host. However, current efforts show great advances in the development of synthetically produced oligosaccharides and bioconjugation. This review evaluates the advances of glycoconjugate vaccines in the last five years. We focus on developments regarding both new carriers and antigens. Innovative developments regarding carriers are outer membrane vesicles, glycoengineered proteins, new carrier proteins, virus-like particles, protein nanocages and peptides. With regard to conjugated antigens, we describe recent developments in the field of antimicrobial resistance (AMR) and ESKAPE pathogens.

Direct MALDI Glycotyping of Glycoproteins toward Practical Subtyping of Biological Samples

The rapid analysis of glycan patterns (glycoforms) of glycoproteins can accelerate their quality control and biomarker discovery. We have focused on the direct analysis of glycoprotein glycoforms using matrix-assisted laser desorption/ionization in-source decay mass spectrometry (MALDI-ISDMS), called MALDI glycotyping. Our results show that the 1,5-diaminonaphthalene (DAN)/2,5-dihydroxybenzoic acid (DHB)/Na matrix can directly analyze the glycoforms in the femtomolar range of intact glycoproteins. The addition of DAN improved the morphology of the solid matrix due to the mixture of DAN and DHB, which significantly contribute to the high sensitivity of this direct analysis. Adding DAN significantly improved the sensitivity of the glycan precursor ions in the TOF/TOF analysis because of its enhanced fragmentation effect as an efficient UV-MALDI matrix. Further, practical glycoform analysis (glycotyping) of diluted biological samples containing glycoproteins, such as egg whites, was also successfully achieved.