The dissertation will discuss the advancement of informative structural biology techniques utilizing a top-down centric workflow with 193nm ultraviolet photodissociation (UVPD) mass spectrometry. Native electrospray ionization is used to transport proteins to the gas phase in a native-like state, then UVPD is used for structural characterization to reveal ligand binding sites within a protein-ligand complex as well as detect conformational changes based upon the suppression or enhancement of backbone cleavages. Conformational changes induced by ligand exchange or removal and single amino acid mutations as well as combinations of the two (ligands and mutations) are investigated. The rich fragmentation patterns of UVPD are also used for structural characterization of crosslinked proteins. Typically these crosslinking experiments are performed by bottom-up mass spectrometry with has significant shortcomings. The main drawback is the need for proteolysis which cuts proteins into small peptides, thus increasing the complexity of the samples and its subsequent analysis. Additionally this proteolysis step loses the post-translation modification information or amino acid mutations that may be driving a specific protein-protein interaction. Top-down methods avoid protein digestion and thus are used to directly evaluate the protein interactions or protein complexes. These two methodologies will bring the mass spectrometry and structural biology community a step closer to the realization of high-throughput structural biology for proteins and their interactions with other proteins and small molecules.

Photon-based tandem mass spectrometry provides a versatile ion activation strategy for the analysis of polypeptides, proteins, and lipids. 351-nm ultraviolet photodissociation mass spectrometry (UVPD-MS) is a facile and selective tandem dissociation technique used to elucidate chromophore-modified peptides within large mixtures. A bis-aryl chromogenic chemical probe was utilized to target solvent exposed primary amine residues within native protein states. Collision-induced dissociation (CID) was employed to indiscriminatly characterize the complete proteolytic digest while chromophore containing peptides were selectively dissociated with 351-nm UVPD; thus streamlining the identification of targeted peptides with structurally informative residues. Protein amine residue reactivities were then compared with predicted solvent exposures to elucidate protein tertiary structures, their mechanistic properties, and ligand-binding interactions. High-energy 193-nm UVPD is a fast, high-energy tandem mass spectrometry method and frequently generates fragment ions typically inaccessible to CID-based methods. Native mass spectrometry was coupled to top-down 193-nm UVPD for the gas phase characterization of non-covalent protein-ligand and protein-protein complexes. This method yielded a unique array of fragment ions for a comprehensive analysis of protein structures. UVPD of non-covalent complexes generated many polypeptide backbone fragments to characterize the primary sequence of proteins. Furthermore, top-down UVPD engendered cleavages with intact electrostatic interactions; this provided insight into the binding interfaces within protein-ligand complexes and the higher order structural architectures of oligomeric complexes. High-resolution 193-nm UVPD was paired with high performance liquid chromatography (LC) for the streamlined structural analysis of amphiphilic glycolipids within complex mixtures. For all glycolipids, UVPD provided the most comprehensive structural analysis tool by affording a diverse array of fragment ions to characterize both hydrophobic and hydrophilic moieties. UVPD based LC-MS separations of gangliosides shed light on the ceramide lipid bases, glycan moieties, and their isobaric structural variants. UVPD activation of lipid A and lipooligosaccharides (LOS) compounds generated a mixture of C-C, C-O, and C-N fragment ions to illustrate the hydrophobic acyl structures, while cleavages within the glycosidic, and cross-ring cleavages allowed the determination of acylation patterns. Novel LC-MS separation strategies were developed to elucidate and structurally characterize complex mixtures of lipopolysaccharide containing compounds.

Ultraviolet photodissocation (UVPD) mass spectrometry was used for high mass accuracy top down characterization of two proteins labeled by the chemical probe, S-ethylacetimidate (SETA), in order to evaluate conformational changes as a function of denaturation. The SETA labeling/UVPD-MS methodology was used to monitor the mild denaturation of horse heart myoglobin by acetonitrile, and the results showed good agreement with known acetonitrile and acid unfolding pathways of myoglobin. UVPD outperformed another ion activation method, electron transfer dissociation (ETD), in terms of sequence coverage, allowing the SETA reactivity of greater number of lysine amines to be monitored and thus providing a more detailed map of myoglobin. This strategy was applied to the third zinc-finger binding domain, domain C, of PARP-1 (PARP-C), to evaluate the discrepancies between the NMR and crystal structures which reported monomer and dimer forms of the protein, respectively. The trends reflected from the reactivity of each lysine as a function of acetonitrile denaturation supported that PARP-C exists as a monomer in solution with a close-packed C-terminal alpha helix. Additionally, those lysines for which the SETA reactivity increased under denaturing conditions were found to engage in tertiary polar contacts such as salt bridging and hydrogen bonding, providing evidence that the SETA/UVPD-MS approach offers a versatile means to probe the interactions responsible for conformational changes in proteins. UVPD mass spectrometry was also employed to investigate the structure of holo-myoglobin as well as its apo form transferred to the gas phase by native electrospray. The fragmentation yields from UVPD showed the greatest overall correlation with B-factors generated from the crystal structure of apo-myoglobin, particularly for the more disordered loop regions. Comparison of UVPD of holo- and apo- myoglobin revealed similarities in fragmentation yields, particularly for the lower charge states (8 and 9+), but those regions involved in harboring the heme group (for the holo form) exhibited significantly lower fragmentation than the apo-myoglobin state. Both holo- and apo-myoglobin exhibited low fragmentation yields for the AGH helical core (reflecting its highest stability).

Structural biology studies aimed at the elucidation of protein-dependent disease mechanisms have traditionally relied on high-resolution techniques, including X-ray crystallography, nuclear magnetic resonance, and cryogenic electron microscopy. While such methodologies remain standard for gaining information on the core structure of proteins, specific drawbacks including time or large sample quantities associated with these approaches have spawned the development of other pipelines. Mass spectrometry (MS) is one such tool that has gained traction as a rapid and sensitive low-resolution structural biology technique. Routinely protein complexes of interest are reacted in solution with covalent chemical probes to preserve structural information prior to enzymatic digestion and mass spectrometric read-out. However, with the advent of native MS, protein complexes can now be efficiently transferred intact into the gas phase using high ionic strength solutions while retaining structures reminiscent of their solution conformations, and directly interrogated using MS/MS methods. Ultraviolet photodissociation (UVPD) is one such ion activation method that has been extensively developed to break apart protein complexes in a manner that allows conclusions about structure to be drawn based on the fragmentation behavior. The work presented here leverages native mass spectrometry in conjunction with 193 nm UVPD to probe a variety of biologically important protein-ligand and protein-protein complexes. The utility in a native UVPD-MS approach for structural examination of protein-ligand complexes is demonstrated through characterization of conformational changes associated with the catalytic cycle of a phosphotransferase enzyme as well as elucidation of structural changes resulting from mutation or inhibition of an enzyme responsible for conferring antibiotic resistance to bacteria. An oncogenic protein and several clinical variants bound to a downstream effector protein provides an example of the capabilities of native MS and UVPD to characterize the structure of a protein-protein complex. Native UVPD-MS is also used for epitope mapping of the main antigenic determinant of the influenza virus. Aimed at improving analysis of larger complexes, multistage native UVPD-MS is developed to probe the structure of a protein implicated in chemotherapeutic resistance in glioblastoma tumors. Lastly, uniting on-line capillary electrophoresis (CE) with multistage native UVPD-MS offers a high-throughput workflow for structural characterization of ribosomal protein complexes

The utility of 193 nm ultraviolet photodissociation (UVPD) and negative electron transfer dissociation (NETD) for the characterization of peptide anions was systematically evaluated. UVPD outperformed NETD in nearly all metrics; however, both methods provided complementary information to traditional collision induced dissociation (CID) of peptide cations in high throughput analyses. In order to enhance the performance of NETD, activated ion negative electron transfer dissociation (AI-NETD) methods were developed and characterized. The use of low-level infrared photoactivation or collisional activation during the NETD reaction period significantly improved peptide anion sequencing capabilities compared to NETD alone. Tyrosine deprotonation was shown to yield preferential electron detachment upon NETD or UVPD, resulting in N - C[alpha] bond cleavage N-terminal to the tyrosine residue. LC-MS/MS analysis of a tryptic digest of BSA demonstrated that these cleavages were regularly observed under high pH conditions. Transmission mode desorption electrospray ionization (TM-DESI) was coupled with 193 nm UVPD and CID for the rapid analysis and identification of protein digests. Comparative results are presented for TM-DESI-MS/CID and TM-DESI-MS/UVPD analyses of five proteolyzed model proteins. In some cases TM-DESI/UVPD outperformed TM-DESI-MS/CID due to the production of an extensive array of sequence ions and the ability to detect low m/z product ions. 193 nm UVPD was implemented in an Orbitrap mass spectrometer for characterization of intact proteins. Near-complete fragmentation of proteins up to 29 kDa was achieved. The high-energy activation afforded by UVPD exhibited far less precursor ion charge state dependence than conventional methods, and the viability of 193 nm UVPD for high throughput top-down proteomics analyses was demonstrated for the less 30 kDa protein from a fractionated yeast cell lysate. The use of helium instead of nitrogen as the C-trap and HCD cell bath gas and trapping ions in the HCD cell prior to high resolution mass analysis significantly reduced the signal decay rate for large protein ions. As a result, monoclonal IgG1 antibody was isotopically resolved and mass accurately determined. A new high mass record for which accurate mass and isotopic resolution has been achieved (148,706.3391 Da ± 3.1 ppm) was established.

Access to high resolution mass spectrometers and high energy modes of activation such as electron- and photon-based modalities have enabled wider adoption of top-down methodologies, or strategies that allow the study of intact proteins. However, interpretation of MS/MS spectra of large proteins remains difficult owing to spectral congestion, charge capacity limitations, and other challenges. In particular, for ultraviolet photodissociation (UVPD) of intact proteins, a single laser pulse is typically used to avoid secondary dissociation of fragment ions that occurs when multiple pulses are employed. Consequently, a large amount of the precursor ion population remains undissociated, meaning a large portion of the potential signal is not effectively utilized. Secondary dissociation results in the generation of less informative small terminal and internal fragment ions. Internal fragments are typically ignored due to the computational challenges associated with accounting for them. The following research focuses on the use of fragment ion protection (FIP) during 193 nm UVPD to counter secondary dissociation when utilizing multiple laser pulses and the exploration of the benefits and pitfalls when considering internal fragment ions generated by 193 nm UVPD. In, summary, FIP increased the center sequence coverage of large proteins, but there is room for improvement. The inclusion of internal fragment ions can aid in enhancing the sequence coverage of intact proteins. However, the majority of internal fragment ions are not reliably identified across multiple replicates, reflecting a high risk of false positive identifications when they are considered. These findings are described in this thesis

This book highlights current approaches and future trends in the use of mass spectrometry to characterize protein therapies. As one of the most frequently utilized analytical techniques in pharmaceutical research and development, mass spectrometry has been widely used in the characterization of protein therapeutics due to its analytical sensitivity, selectivity, and specificity. This book begins with an overview of mass spectrometry techniques as related to the analysis of protein therapeutics, structural identification strategies, quantitative approaches, followed by studies involving characterization of process related protein drug impurities/degradants, metabolites, higher order structures of protein therapeutics. Both general practitioners in pharmaceutical research and specialists in analytical sciences will benefit from this book that details step-by-step approaches and new strategies to solve challenging problems related to protein therapeutics research and development.