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)-based protein footprinting characterizes protein structure and protein-ligand interactions by interrogating protein solvent-accessible surfaces by using chemical reagents as probes. The method is highly applicable to protein or protein-ligand complexes that are difficult to study by conventional means such as X-ray crystallography and nuclear magnetic resonance. In this dissertation, we describe the development and application of MS-based protein footprinting from three perspectives, including I) protein aggregation and amyloid formation (Chapter 2-3), II) protein-ligand interactions (Chapter 4-5), and III) in-cellulo structures and dynamic motion of membrane proteins (Chapter 6). Fast Photochemical Oxidation of Proteins (FPOP) is the main methodology implemented in the work presented in this dissertation. Chapter 1 provides an overview of FPOP and discusses its fundamentals as well as its important applications in both academic research and biotechnology drug development. In Part I, Chapter 2 covers the early method development of FPOP for monitoring amyloid beta (A[beta]) aggregation. In this work, we demonstrated the high sensitivity and spatial resolution of the method in probing the solvent accessibility of A[beta] at global, sub-regional, and some amino-acid residue levels as a function of its aggregation, and revealed A[beta] species at various oligomeric states identified by their characteristic modification levels. In Chapter 3, we extended the application of the platform to assess the effect of a putative polyphenol inhibitor on amyloid formation and to provide insights into the mechanism of action of the inhibitor in remodeling A[beta] aggregation pathways. In Part II, we evaluated different protein footprinting techniques, including FPOP, hydrogen-deuterium exchange (HDX), and carboxyl group footprinting, for probing protein-ligand (drug candidates) interaction in the context of a therapeutic development. Chapter 4 focused on protein-protein interaction by investigating the epitope of IL-6 receptor for two adnectins that have similar apparent biophysical properties. In Chapter 5, we probed the hydrophobic binding cavity of bromodomain protein for a small molecule inhibitor. This study serves as an example of interrogating protein-small molecule interactions. The two studies in Part II demonstrate the unique capabilities and limitations of protein footprinting methods in protein structural characterization. In Part III, we pushed the boundary of MS-based protein footprinting by applying the method to footprint live cells and investigate the dynamic structures/motion of membrane-transport proteins in their native cellular environment. We employed protein engineering, suspension cell expression and isotopic-encoded carboxyl group footprinting to identify salt bridges in two proteins, GLUT1 and GLUT5, that control their alternating access motions for substrate translocation. With functional analysis and mutagenesis, live-cell footprinting provides new insights into the transport mechanism of proteins in the major facilitator superfamily. The five studies in the dissertation demonstrate the powerful capability of MS-based protein footprinting in protein structural biology and biophysics research. The method also holds great potential in studying more complicated biological systems and solving demanding problems related to protein structure and properties.

Presents a wide variety of mass spectrometry methods used to explore structural mechanisms, protein dynamics and interactions between proteins. Preliminary chapters cover mass spectrometry methods for examining proteins and are then followed by chapters devoted to presenting very practical, how-to methods in a detailed way. Includes footprinting and plistex specifically, setting this book apart from the competition.

PROVIDES STRATEGIES AND CONCEPTS FOR UNDERSTANDING CHEMICAL PROTEOMICS, AND ANALYZING PROTEIN FUNCTIONS, MODIFICATIONS, AND INTERACTIONS—EMPHASIZING MASS SPECTROMETRY THROUGHOUT Covering mass spectrometry for chemical proteomics, this book helps readers understand analytical strategies behind protein functions, their modifications and interactions, and applications in drug discovery. It provides a basic overview and presents concepts in chemical proteomics through three angles: Strategies, Technical Advances, and Applications. Chapters cover those many technical advances and applications in drug discovery, from target identification to validation and potential treatments. The first section of Mass Spectrometry-Based Chemical Proteomics starts by reviewing basic methods and recent advances in mass spectrometry for proteomics, including shotgun proteomics, quantitative proteomics, and data analyses. The next section covers a variety of techniques and strategies coupling chemical probes to MS-based proteomics to provide functional insights into the proteome. In the last section, it focuses on using chemical strategies to study protein post-translational modifications and high-order structures. Summarizes chemical proteomics, up-to-date concepts, analysis, and target validation Covers fundamentals and strategies, including the profiling of enzyme activities and protein-drug interactions Explains technical advances in the field and describes on shotgun proteomics, quantitative proteomics, and corresponding methods of software and database usage for proteomics Includes a wide variety of applications in drug discovery, from kinase inhibitors and intracellular drug targets to the chemoproteomics analysis of natural products Addresses an important tool in small molecule drug discovery, appealing to both academia and the pharmaceutical industry Mass Spectrometry-Based Chemical Proteomics is an excellent source of information for readers in both academia and industry in a variety of fields, including pharmaceutical sciences, drug discovery, molecular biology, bioinformatics, and analytical sciences.

Two important biophysical characteristics of proteins, their interaction with ligands and their post-translational modifications, modulate various biological processes including signal transduction, chemical synthesis, and cell function. Protein-ligand interactions include the interactions with protein, peptide, DNA, and metal. Characterization of the physical properties of these interactions (binding interfaces, binding affinities, and the protein conformational changes due to the binding) is essential in understanding the mechanism of related diseases and, more importantly, in future drug design. Mass spectrometry, with its own revolution and improvement, becomes a powerful tool in protein and peptide analysis. In this thesis, we applied two mass spectrometry-based strategies, proteomics and protein footprinting, to characterize these biophysical properties of three disease-related proteins, connexin 43 (Cx43), troponin, and apolipoprotein E (ApoE), and Fenna-Matthews-Olson protein (FMO), which is the key factor in energy transfer of the photosynthetic system of green sulfur bacteria. By the combination of standard proteomics workflow and two fragmentation methods, collision-induced dissociation (CID) and electron transfer dissociation (ETD), we successfully identified 15 serine residues, including one novel site, in the Cx43-CT that are phosphorylated by CaMKII, the activity of which may be important in regulating Cx43 in normal and diseased hearts. We further utilized hydrogen/deuterium exchange (H/DX), one mass spectrometry-based protein footprinting strategy, to examine the binding affinities of troponin C (TnC), a cardiac disease-related protein, with its four metal binding ligands (Ca2+), and their binding order. We then expanded this approach to elucidate the dynamics of TnC within the complex and its interactions with other subunits (TnT and TnI) at peptide-level resolution. This same approach was also applied to two protein-ligand complexes: (1) the interaction of FMO and its binding partner, CsmA baseplate protein, in which the orientation of FMO between chlorosome and membrane can be confirmed, and (2) the interaction of ApoE and Abeta 40, which are both key factors in Alzheimer's disease. Moreover, we improved the spatial resolution of H/DX to residue-level by conducting ETD fragmentation in the study of ApoE oligomerization. Our results reveal, for the first time, the amino acid residues involved in its self-oligomerization. These six applications of mass spectrometry-based approaches show their potential in the characterization of different protein biophysical properties. The investigation of a more complex protein system can then be pursued.