Proteins carry a plethora of post-translational modifications (PTMs), such as glycosylation or phosphorylation, which may affect stability and activity. Analytical strategies are needed to... Show moreProteins carry a plethora of post-translational modifications (PTMs), such as glycosylation or phosphorylation, which may affect stability and activity. Analytical strategies are needed to investigate these PTMs in their native state to determine the link between structure and function. The coupling of native separation techniques with mass spectrometry (MS) has emerged as a powerful tool for in-depth protein characterization. Yet obtaining high ionization efficiency still can be challenging. Here, we explored the potential of dopant-enriched nitrogen (DEN) gas to improve nano-electrospray ionization (nano-ESI)-MS of native proteins after anion exchange chromatography. The dopant gas was enriched with different dopants (acetonitrile, methanol, and isopropanol) and the effects were compared with the use of solely nitrogen gas for six proteins covering a wide range of physicochemical properties. The use of DEN gas resulted generally in lower charge states, independent of the selected dopant. Moreover, less adduct formation was observed, particularly for the acetonitrile-enriched nitrogen gas. Importantly, striking differences in MS signal intensity and spectral quality were observed for extensively glycosylated proteins, where isopropanol- and methanol-enriched nitrogen appeared to be most beneficial. Altogether, the use of DEN gas improved nano-ESI of native glycoproteins and increased spectral quality for highly glycosylated proteins that normally suffer from low ionization efficiency. Show less
Proteins are widely known as key players that fulfill crucial roles at the molecular level in the human body but also for their involvement in many processes in everyday life. For example, proteins... Show moreProteins are widely known as key players that fulfill crucial roles at the molecular level in the human body but also for their involvement in many processes in everyday life. For example, proteins can be used as medicine in health care or for their enzymatic function in the food industry. All these proteins do not exist as a single species but rather as a complex mixture of structural variants, so-called proteoforms. This heterogeneity results mainly from the presence of post-translational modifications (PTMs), such as glycosylation and glycation. To further complicate this matter, these PTMs can induce structural as well as functional changes. To allow in-depth structural and functional characterization of these proteoforms, novel analytical approaches are required to resolve proteoform heterogeneity while persevering protein nativity. The hyphenation of native separation techniques with mass spectrometry has emerged as a powerful approach to reliably study these aspects. The work in this thesis describes the (further) development and application of such methodologies for biopharmaceutical and biotechnological products. Show less
Antibody-based drugs are the largest class of biopharmaceuticals produced. They are currently employed to treat diverse diseases such as cancer, cardiovascular or neuronalogical diseases. Whereas... Show moreAntibody-based drugs are the largest class of biopharmaceuticals produced. They are currently employed to treat diverse diseases such as cancer, cardiovascular or neuronalogical diseases. Whereas some years ago, efforts were focused on developing classical monoclonal antibodies (mAbs), nowadays there is a trend towards engineered antibodies with enhanced functions, such as bispecific antibodies (BsAbs). These molecules increase on structural complexity and bring new challenges for their analytical characterization. Furthermore, the continuous development of new antibody treatments and molecules also increases the pressure in the analytical labs longing for more automation and high-throughput mass spectrometric analysis. This thesis addresses these aspects and provide solutions for improved and efficient characterization of novel antibody therapeutics focusing on mass spectrometric approaches. These approaches are based on multidimensional liquid chromatography or capillary electrophoresis hyphenated to mass spectrometry or on the application of in-source decay fragmentation. Next to structural characterization, in this thesis MS-based approaches have been developed for their functional characterization permitting to study the relationships between antibody structure and function. Show less
Early detection of prostate cancer may lead to the overdiagnosis and overtreatment of patients as well as missing significant cancers. The current diagnostic approach uses elevated serum... Show moreEarly detection of prostate cancer may lead to the overdiagnosis and overtreatment of patients as well as missing significant cancers. The current diagnostic approach uses elevated serum concentrations of prostate-specific antigen (PSA) as an indicator of risk. However, this test has been widely criticized as it shows poor specificity and sensitivity. In order to improve early detection and diagnosis, several studies have investigated whether different PSA proteoforms are correlated to prostate cancer. Until now, studies and methodologies for the comprehensive characterization of PSA proteoforms from biofluids are scarce. For this purpose, we developed an intact protein assay to analyze PSA by capillary electrophoresis-electrospray ionization-mass spectrometry after affinity purification from patients? urine. Here, we determined six proteolytic cleavage variants. In regard to glycosylation, tri-, di-, mono- and non-sialylated complex-type N-glycans were found on non-cleaved PSA, as well as the non-glycosylated variant. The performance of the intact protein assay was assessed using a pooled sample, obtaining an inter-day variability of 15%. Furthermore, urinary patient samples were analyzed by intact protein analysis and a bottom-up approach (glycopeptide analysis). This combined approach revealed complimentary information on both levels, demonstrating the benefit of using two orthogonal techniques to provide a thorough profile of urinary PSA.Significance: The detection of clinically relevant prostate cancer requires a more specific and sensitive biomarker and, in this case, several PSA proteoforms may be able to aid or improve the current PSA test. However, a comprehensive analysis of the intact PSA proteoform profile is still lacking. This study investigated the PSA proteoforms present in urine and, in particular, determined the relative contribution of cleaved PSA and noncleaved PSA forms to the total glycosylation profile. Importantly, intact protein analysis did not require further sample treatment before being measured by CE-ESI-MS. Furthermore, its glycosylation was also assessed in a bottom-up approach to provide complementary information. Overall, these results represent an important basis for future characterization and biomarker studies. Show less
Lipoprotein(a) (Lp(a)) is an independent risk factor in the development of atherosclerotic cardiovascular diseases (ASCVD) and calcific aortic valve disease (CAVD). Lp(a) is an LDL-like particle to... Show moreLipoprotein(a) (Lp(a)) is an independent risk factor in the development of atherosclerotic cardiovascular diseases (ASCVD) and calcific aortic valve disease (CAVD). Lp(a) is an LDL-like particle to which apolipoprotein (a) (apo(a)) is covalently bound. Apo(a) contains a variable number of kringle IV repeats, a kringle V and a protease domain. Serum/plasma Lp(a) concentrations are traditionally expressed as total particle mass in mg/L. Concern has arisen lately as flawed Lp(a) mass tests have masked its clinical utility.The determinants of variability in Lp(a) composition were investigated, including the apo(a) size polymorphism, post-translational modifications -N- and O-glycosylation- and the lipid:protein ratio. Depending on the number of kringle IV-2 repeats, the theoretical protein content of the Lp(a) particle varies between 30 and 46 (w/w) %, which inescapably confounds Lp(a) mass measurements.The authors advocate that reporting of Lp(a) particle concentrations in mass units is metrologically inappropriate and should be abandoned, as it results in systematically biased Lp(a) results. Enabling technology, such as mass spectrometry, allows unequivocal molecular characterization of the apo(a) measurand(s) and accurate quantitation of apo(a) in molar units, unaffected by apo(a) size polymorphism. To guarantee that Lp(a)/apo(a) tests are fit-for-clinical-purpose, basic metrology principles should be implemented upfront during test development. Show less
