Hydrogen exchange mass spectrometry is widely recognized for its ability to probe the structure and dynamics of proteins. The application of this technique is becoming widespread due to its versatility for providing structural information about challenging biological macromolecules such as antibodies, flexible proteins and glycoproteins. Although the technique has been around for 25 years, this is the first definitive book devoted entirely to the topic. Hydrogen Exchange Mass Spectrometry of Proteins: Fundamentals, Methods and Applications brings into one comprehensive volume the theory, instrumentation and applications of Hydrogen Exchange Mass Spectrometry (HX-MS) - a technique relevant to bioanalytical chemistry, protein science and pharmaceuticals. The book provides a solid foundation in the basics of the technique and data interpretation to inform readers of current research in the method, and provides illustrative examples of its use in bio- and pharmaceutical chemistry and biophysics In-depth chapters on the fundamental theory of hydrogen exchange, and tutorial chapters on measurement and data analysis provide the essential background for those ready to adopt HX-MS. Expert users may advance their current understanding through chapters on methods including membrane protein analysis, alternative proteases, millisecond hydrogen exchange, top-down mass spectrometry, histidine exchange and method validation. All readers can explore the diversity of HX-MS applications in areas such as ligand binding, membrane proteins, drug discovery, therapeutic protein formulation, biocomparability, and intrinsically disordered proteins.

ABSTRACT: Proteins are vital macromolecules of every living cell. They undertake a variety of tasks that are essential for life. Most proteins function in assemblies rather than individually. Protein function is strongly correlated to structure and elucidation of both aspects of the protein is indispensable to understand its mechanism of action. Among several structural characterization techniques, solution-phase hydrogen/deuterium exchange monitored by mass spectrometry has emerged in the last 25 years as a powerful tool to study protein-protein interaction and dynamics. In the first half of this dissertation, we describe several aspects of method development that allowed tackling of previously inconceivable biological problems. In the second half, we demonstrate how this tool is applied to study muscle biochemistry; particularly, the troponin complex and myosin. In Chapter 1, we introduce the method, its mechanism, each of its sequential steps improvements which overcame multiple limitations and permitted its application to wide variety of biological problems. In Chapter 2, we describe the optimization of the separation step to minimize back-exchange, a major drawback of the technique. Chapter 3. demonstrates how isotopic depletion of proteins could be advantageous for peptide fragment identification, reduction of the mass spectral complexity, and the increase of the signal-to-noise ratio. In a different aspect of method development, we present a global analysis algorithm in Chapter 4, to manage the enormous amount of data, increase throughput, and most importantly, take advantage of peptide fragment overlap to increase sequence resolution. On the other hand, the second half of the dissertation is dedicated to muscle biochemistry. Troponin is a heterotrimeric complex involved in muscle regulation. The structure of a truncated version of the cardiac isoform of the complex was only solved in the calcium-saturated state. In Chapter 5, we apply hydrogen/deuterium exchange on full length troponin in the calcium-saturated and the calcium-free states to understand how the troponin subunits fit together and what are the conformational changes induced by calcium. Moreover, Chapter 6 describes the allosteric changes induced by phosphorylation the inhibitory subunit N-terminal extension, specific to the cardiac isoform of the complex. Finally, in Chapter 7, we elucidate the conformational changes that accompany the transition of myosin V (a molecular motor) from the post-rigor (ATP-analog bound) to the rigor-like (nucleotide-free) states, thus characterizing new features of the powerstroke.

Proteins are not static objects. They have a great variety of internal motions with different amplitudes and different timescales. These internal motions play an important role in catalytic processes. Therefore, the existence of an intimate relationship between protein dynamics and protein function is widely accepted. Due to the significance of protein dynamics, techniques have been developed to study protein dynamics including nuclear magnetic resonance (NMR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and mass spectrometry (MS). Compared with NMR and EPR spectroscopy, MS has less stringent sample requirements, including protein concentration and protein size. Moreover, the mass accuracy, sensitivity, and faster data analysis also have contributed to the rapid growth of MS based techniques. Hydrogen-deuterium exchange mass spectrometry (HDX-MS), a combination of HPLC and MS, has become a common and sensitive tool to probe protein structural flexibility and solution dynamics. In this dissertation, HDX-MS was applied to study dynamic changes of proteins due to substrate binding and protein-protein interactions. The GT-A glycosyltransferase glucosyl-3-phosphoglycerate synthase from Mycobacterium tuberculosis (MtGpgS) catalyzes the first step of biosynthesis of 6-O-methylglucose lipopolysaccharides (MGLPs), which are essential to growth and existence of mycobacterium. The HDX-MS data revealed that the two substrates UDP-glucose (UDPG) and 3-phosphoglycerate (3PGA) can bind to MtGpgS independently, disagreeing with the previous proposal that 3PGA can only bind to MtGpgS after UDPG. Moreover, 3PGA was found to bind to or allosterically affect the UDPG binding site. Furthermore, the HDX-MS data revealed that MtGpgS may provide a necessary conformation for UDPG binding, while it goes through a large conformational change on 3PGA binding. The GT-B glycosyltransferase MshA from Corynebacterium glutamicum (CgMshA) catalyzes the initial step of mycothiol biosynthesis. A large conformational change was observed in CgMshA on nucleotide binding by superimposing APO structure of CgMshA and complex structure with UDP. HDX-MS was utilized to study conformational changes of CgMshA on substrate binding from the aspect of dynamics, providing a complementary to static structures. The HDX-MS data showed that both substrates uridine diphosphate glucose-N-acetylglucosamine (UDP-GlcNAc) and 1-L-myo-inositol-1-phosphate (I1P) can bind to CgMshA independently, but the I1P binding is not productive since it binds to an uncorrect site. Moreover, the I1P binding can lead to dynamic changes of CgMshA, while only UDP-GlcNAc can induce the major conformational change of CgMshA. Furthermore, the 3PGA binding cannot induce further dynamic changes of CgMshA in the presence of UDP. HDX-MS was also employed to study dynamic changes of protein complex SufBC2D from Escherichia coli on ADP/Mg2+ binding. This complex is responsible for Fe-S cluster assembly under oxidative stress. The crystal structure of SufBC2D complex has been determined, while little dynamic information is known. So HDX-MS was applied to study dynamic changes of the SufBC2D complex. The HDX-MS data revealed that SufC has a significant conformational change, which may be required by ATP binding and hydrolysis. Moreover, SufB and SufD are detected to have dynamic changes due to SufC conformational changes. These dynamic changes suggest that SufB-SufD protomer may have a conformational change in order to provide a suitable conformation for Fe-S cluster assembly. This work demonstrates that HDX-MS can be effectively used to study protein-ligand and protein-protein interactions, as well as the accompanying changes in structural dynamics. HDX-MS data detects substrate binding mechanism and conformational changes that are not available through x-ray crystallography. With these advantages, HDX-MS has been applied in study of protein structure and dynamics, studying protein-ligand and protein-protein interactions, protein folding, as well as protein therapeutics discovery and development.

Mass spectrometry (MS) has emerged as a powerful tool for epitope mapping, protein-ligand interaction, protein-protein interaction, aggregation, and effect of solution environment on protein conformation because they provide high-throughput data with relatively high structural resolution. Two popular MS-based approaches are hydrogen deuterium exchange-mass spectrometry (HDX-MS) and fast photochemical oxidation of proteins (FPOP), which complement classical biophysical and biochemical techniques in achieving higher structural resolution. The research presented in this dissertation is focused on the application of mass spectrometry-based footprinting techniques in characterizing the biophysical properties of Part I: pH-dependent conformation change of diphtheria toxin T domain (Chapters 2-4)); Part II: Ca2+ binding proteins and the role of Ca2+ regulation (Chapters 5-6); and Part III: protein-protein interaction including epitope mapping of IL-23 (Chapter 7) and Marburg virus protein VP24 (Chapter 8). Chapter 1 serves as an introduction to mass spectrometry instrumentation and standard LC-MS workflow. Two mass spectrometry based-footprinting techniques are introduced: (1) hydrogen deuterium exchange (HDX), and (2) fast photochemical oxidation of proteins (FPOP). Part I focuses on the development of pH-dependent HDX-MS for the conformation study of diphtheria toxin T domain. In Chapter 2, we describe the use pH-dependent HDX to study the pH-dependent conformation change of wild-type diphtheria toxin T domain monomer along its translocation pathway. In Chapter 3, we study the pH-dependent dissociation and reformation of T domain dimer. In Chapter 4, we apply the same method to a T domain mutant H223Q to further investigate the role of key histidine residues in triggering the conformation change. Part II focuses on the application of HDX mass spectrometry for the study of calcium binding proteins. Chapter 5 describes the Ca2+-binding property of ACaM and its Ca2+-regulated interaction with myosin VI. In chapter 6, HDX is also applied to an EF-hand Ca2+ binding protein, DREAM, for the study of its Ca2+ binding sites and stoichiometry. Part III of the dissertation focuses on the development and application of MS-based footprinting methods to investigate protein-protein interaction. Chapter 7 describes the methodology of fast photochemical oxidation of proteins (FPOP) for epitope mapping of IL-23 interacting a therapeutic antibody from Bristol-Myers Squibb. Chapter 8 discusses the use of HDX, FPOP, and NEM chemical labeling for the study of Marburg virus protein VP24 and its interaction with the host protein Keap1 Kelch domain. These seven studies on characterization of protein conformation dynamics, Ca2+ binding protein, and protein-protein interaction show the successful application of mass spectrometry in the structural study of large biomolecules.

Mass spectrometry (MS) is a powerful tool for analyzing biomolecules. In this dissertation, we present development and applications of carbene reagents for protein footprinting and hydrogen/deuterium exchange (HDX) for characterization of a protein complex that is important for nuclear transportation of an Ebola virus protein. In Chapter 1, we describe the basic principles and detailed configurations of Photochemical Oxidation of Proteins (FPOP). FPOP utilizes hydroxyl radicals to probe protein higher order structure. To expand the radical reagents used for FPOP, we explored the feasibility of generating carbenes by laser photolysis of diazirines in our FPOP system for protein footprinting in Chapters 2 and 3. In Chapter 4, we took advantage of one diazirine reagent and studied the structural differences of apolipoprotein E3 and E4, and their interactions with a small molecule structural corrector. In chapter 5, we described a novel method to combined carbene footprinting with hydroxyl radical footprinting in a two-laser FPOP platform. We also applied several other MS-based methods in Chapter 6 to characterize protein complexes that are involved in nuclear transportation of Ebola VP24 protein.