Application of hydrogen deuterium exchange mass spectrometry in protein-ligand and protein-protein interactions

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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.

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