One important function of intracellular protein degradation is to selectively destroy misfolded or damaged proteins, as accumulate in various human diseases and during aging. Our primary goal is to understand further the functioning of the ubiquitin proteasome pathway and the involvement of molecular chaperons in this process. Most protein breakdown in mammalian cells is catalyzed by the 26S proteasome, whose 19S regulatory particle contains six ATPases which function as molecular chaperones. To understand how these ATPases unfold and translocate substrates into the core 20S proteasome, we are also studying the simpler, homologous ATPase complex, PAN, which activates proteolysis by 20S proteasomes in archaea. We recently discovered that upon ATP-binding, a conserved C-terminal sequence (HbYX motif) in these ATPases docks into pockets in the 20S's outer ring and like a "key-in-a-lock" triggers opening of its gated channel for substrate entry. A major goal will be to elucidate further the molecular events for gate-opening and its structural basis. In the eukaryotic 26S, the six ATPases and seven 20S ?-subunits differ, and gate opening is restricted to two ATPases. We hope to learn which C-termini dock into which 20S pockets and whether other proteasome regulators (BLM10, PI131) and p97/cdc48 that contain the HbYX motif activate 20S proteasomes similarly. We have dissociated proteasomal degradation into a series of ATP-requiring steps, and hope to elucidate further this multistep reaction sequence. We shall explore whether the eukaryotic 26S utilizes additional reaction steps in degrading ubiquitin-conjugated proteins. We've found that the six ATPase subunits interact through negative cooperativity and identified in PAN two substrate-binding domains whose function is nucleotide-dependent. We hope to clarify the functional significance in protein degradation of these cooperative interactions and the associated conformational changes. We recently found that increased temperatures and oxygen radicals in yeast cause the degradation specifically of newly synthesized proteins, without affecting breakdown of most cell proteins. We hope to clarify further the roles of different ubiquitination enzymes and molecular chaperones in their degradation and to identify the newly synthesized proteins most sensitive to such damage. In harsh conditions that damage cell proteins (e.g. heat-shock, oxidative stress, near-freezing temperatures), yeast produce large amounts of the "chemical chaperone", trehalose, which enhances cell viability. We recently found that trehalose is also required for efficient protein degradation, even in normal cells. The mechanisms of this unexpected new protective function of trehalose will be investigated.
A prominent feature of many inherited and neurodegenerative diseases and of the aging process is the accumulation of misfolded proteins, as may result from mutations or free-radical damage. The overall goal of our studies is to clarify the biochemical mechanisms by which such abnormal proteins are selectively degraded by the ubiqutin-proteasome pathway. These studies are focusing on the molecular mechanisms of the proteasome-regulatory ATPases that bind protein substrates and translocate them into the 20S proteasome for degradation and also on the functions of molecular chaperones in this degradative process.
|Myeku, Natura; Clelland, Catherine L; Emrani, Sheina et al. (2016) Tau-driven 26S proteasome impairment and cognitive dysfunction can be prevented early in disease by activating cAMP-PKA signaling. Nat Med 22:46-53|
|Sha, Zhe; Goldberg, Alfred L (2016) Reply to Vangala et al.: Complete inhibition of the proteasome reduces new proteasome production by causing Nrf1 aggregation. Curr Biol 26:R836-7|
|Zhao, Jinghui; Garcia, Gonzalo A; Goldberg, Alfred L (2016) Control of proteasomal proteolysis by mTOR. Nature 529:E1-2|
|Zhao, Jinghui; Zhai, Bo; Gygi, Steven P et al. (2015) mTOR inhibition activates overall protein degradation by the ubiquitin proteasome system as well as by autophagy. Proc Natl Acad Sci U S A 112:15790-7|
|Lokireddy, Sudarsanareddy; Kukushkin, Nikolay Vadimovich; Goldberg, Alfred Lewis (2015) cAMP-induced phosphorylation of 26S proteasomes on Rpn6/PSMD11 enhances their activity and the degradation of misfolded proteins. Proc Natl Acad Sci U S A 112:E7176-85|
|Tsvetkov, Peter; Mendillo, Marc L; Zhao, Jinghui et al. (2015) Compromising the 19S proteasome complex protects cells from reduced flux through the proteasome. Elife 4:|
|Akopian, Tatos; Kandror, Olga; Tsu, Christopher et al. (2015) Cleavage Specificity of Mycobacterium tuberculosis ClpP1P2 Protease and Identification of Novel Peptide Substrates and Boronate Inhibitors with Anti-bacterial Activity. J Biol Chem 290:11008-20|
|Goldberg, Alfred L; Zhao, Jinghui; Collins, Galen A (2015) Blocking Cancer Growth with Less POMP or Proteasomes. Mol Cell 59:143-5|
|Rock, Kenneth L; FarfÃ¡n-Arribas, Diego J; Colbert, Jeff D et al. (2014) Re-examining class-I presentation and the DRiP hypothesis. Trends Immunol 35:144-52|
|Gavrish, Ekaterina; Sit, Clarissa S; Cao, Shugeng et al. (2014) Lassomycin, a ribosomally synthesized cyclic peptide, kills mycobacterium tuberculosis by targeting the ATP-dependent protease ClpC1P1P2. Chem Biol 21:509-18|
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