Development of top-down mass spectrometry methods for structural characterization of protein macromolecules utilizing 193nm ultraviolet photodissociation
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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.