Date of Award

Spring 5-15-2015

Author's School

Graduate School of Arts and Sciences

Author's Department

Chemistry

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Mass spectrometry (MS)-based biophysical approaches are new "tools" for protein characterization owing to its capability to analyze proteins and protein complexes that range in molecular weight from kDa to MDa. Protein characterization requires more than identifying the primary structure. More importantly, protein high order structures (i.e., secondary, tertiary and quaternary structures) are needed for biological studies. MS has become the major tool in studies of protein primary structure and post translational modifications (PTMs) over the past two decades. Because MS has high sensitivity and fast turnaround, more and more biophysical approaches rely on MS to generate information for protein higher order structures.

One of the emerging biophysical approaches is MS-based protein footprinting. Protein surface regions can be covalently labeled by chemical reagents in a biologically relevant environment. These chemical labels can be read out by MS through either bottom-up or top-down MS proteomics analysis. The outcome provides protein conformational information. Among various chemical labeling strategies, hydrogen deuterium exchange (HDX) is one of the most commonly used approaches in MS-based protein biophysical studies.

HDX-MS is introduced in Chapter 1 by covering the early developments and new applications especially in measuring interaction affinities. Although HDX-MS has been developed for decades, there are still many challenges in protein characterization that require new or improved HDX method development. One such challenge is characterization of protein aggregation. Protein aggregation leads to loss of protein function, and protein aggregates are implicated in several neurodegenerative diseases like Alzheimer's and Parkinson's diseases. A key issue in studies of protein aggregation is real-time monitoring under biologically relevant condition. We developed an HDX-MS-based approach by studying Alzheimer's disease related Ab aggregation, and we described this development in Chapter 2. Ab proteins are labeled by deuterium in a pulsed way during Ab aggregation. The extents of aggregations are monitored by MS as deuterium uptake. This pulsed HDX platform provides peptide-level information about Ab; aggregation. Ligands (drug candidates) were also evaluated with this platform to determine how the drug candidates affect oligomerization (Chapter 3).

Ligand interactions can induce protein conformational changes, which are required in various protein functions like signaling, enzyme activity. Such interactions are fundamental to all biological processes. One of the often used ligands in cells is calcium. Calcium interacts with a variety of calcium-binding proteins, most of which have conserved sequence that form EF-hand motifs to bind calcium. MS-HDX has been an important tool in studies of these typical calcium-binding proteins. Many proteins without an EF-hand motif also require calcium for their function. For example, protein-arginine deiminase (PAD) is an enzyme for arginine citrullination and binds calcium without EF-hand motif. We conducted differential HDX studies on PAD2 protein (Chapter 4). Multiple and cooperative calcium binding of PAD2 are detected by HDX. HDX was further extended by applying protein-ligand titration in an HDX experiment (i.e., Protein-ligand interactions by mass spectrometry, titration and H/D exchange, PLIMSTEX). The calcium binding affinity of each binding site can be elucidated by PLIMSTEX (Chapter 5).

Protein aggregation or ligand-binding induced conformational changes can also be detected by MS-HDX. One significant question in MS-based biophysical studies is how to generate structural information for proteins in the absence of a high resolution structure. In a newly developed platform, we combined a traditional structural biology approach, homology modeling, and MS-HDX to generate a structural model for diheme cytochrome c (DHCC) from Heliobacterium (Chapter 6), a protein for which solvent accessibility information from HDX experiment was used as the guide for homology modeling and used to generate a refined structural model of DHCC by using various computational approaches.

In summary, we describe in this thesis development and application of several new, refined approaches of HDX and analyze protein aggregation, protein-ligand binding and unknown protein structures. We hope other scientists can apply these approaches to solve complicated and demanding biological problems that are difficult to investigate using traditional biophysical methods.

Language

English (en)

Chair and Committee

Michael L Gross

Committee Members

Liviu M Mirica, Robert E Blankenship, John-Stephen Taylor, Weikai Li, Jan Bieschke

Comments

Permanent URL: https://doi.org/10.7936/K7154F6V

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