Chemistry & Biochemistry
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Item Structural and Biophysical Explorations of Protein Degradation Tags(2023) Bonn, Steven Michael; Fushman, David; Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ubiquitin is a 76-amino acid, well-folded and highly stable protein that is highly conserved across all eukaryotes. It is a post-translational modifier of other proteins through itsattachment via an isopeptide bond to a substrate lysine sidechain. Multiple ubiquitin units can be stacked to form a polyubiquitin chain, with chain topologies and cellular outcomes varying based on which of ubiquitin’s lysine residues they are attached to. The most common and well-studied outcome of polyubiquitin attachment is degradation by the proteasome, a massive barrel-shaped protease complex responsible for general protein quality control as well as cell cycle progression. Proteasomes have been discovered in archaea and bacteria, and are controlled by the small archaeal modifier protein (SAMP) and the disordered prokaryotic ubiquitin-like protein (Pup), respectively. Recently, a second bacterial proteasome operon was discovered with a new putative signaling protein, ubiquitin bacterial (UBact). Here, the first investigation of the UBact proteasomal operon is presented. Using nuclear magnetic resonance (NMR) spectroscopy and a variety of biophysical techniques, UBact is demonstrated to be disordered in solution and interact with its putative proteasomal receptor. This sets the groundwork for further studies of the UBact system. Additionally, NMR is used to explore the activity and directionality of various deubiquitinase enzymes responsible for breaking down polyubiquitin chains, and for exploring small molecule binding to ubiquitin chains themselves. This likewise provides a groundwork for further studies of the ubiquitin system, whose dysregulation is responsible for many diseases and is an area of intense therapeutic development.Item INVESTIGATION BY MASS SPECTROMETRY OF THE UBIQUITOME AND PROTEIN CARGO OF EXOSOMES DERIVED FROM MYELOID-DERIVED SUPPRESSOR CELLS(2016) Adams, Katherine R.; Fenselau, Catherine; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Exosomes released by myeloid-derived suppressor cells (MDSC) are 30 nm in diameter extracellular vesicles that have been shown to carry biologically active proteins as well as ubiquitin molecules. Ubiquitin is known to have many functions, including involvement in the formation of exosomes, although the exact role is highly contested. In the study reported here, the proteome and ubiquitome of MDSC exosomes has been investigated by bottom-up proteomics techniques. This report identifies more than 1000 proteins contained in the MDSC exosome cargo and 489 sites of ubiquitination in more than 300 ubiquitinated proteins based on recognition of glycinylglycine tagged peptides without antibody enrichment. This has allowed extensive chemical and biological characterization of the ubiquitinated cohort compared to that of the entire protein cargo to support hypotheses on the role of ubiquitin in exosomes.