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.

Public Health Relevance

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.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM051923-16
Application #
8197829
Study Section
Membrane Biology and Protein Processing (MBPP)
Program Officer
Wehrle, Janna P
Project Start
1995-08-01
Project End
2012-11-30
Budget Start
2011-12-01
Budget End
2012-11-30
Support Year
16
Fiscal Year
2012
Total Cost
$545,966
Indirect Cost
$223,862
Name
Harvard University
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
047006379
City
Boston
State
MA
Country
United States
Zip Code
02115
VerPlank, Jordan J S; Lokireddy, Sudarsanareddy; Feltri, M Laura et al. (2018) Impairment of protein degradation and proteasome function in hereditary neuropathies. Glia 66:379-395
Sha, Zhe; Schnell, Helena M; Ruoff, Kerstin et al. (2018) Rapid induction of p62 and GABARAPL1 upon proteasome inhibition promotes survival before autophagy activation. J Cell Biol 217:1757-1776
Kim, Hyoung Tae; Goldberg, Alfred L (2018) UBL domain of Usp14 and other proteins stimulates proteasome activities and protein degradation in cells. Proc Natl Acad Sci U S A 115:E11642-E11650
Kim, Hyoung Tae; Goldberg, Alfred L (2017) The deubiquitinating enzyme Usp14 allosterically inhibits multiple proteasomal activities and ubiquitin-independent proteolysis. J Biol Chem 292:9830-9839
Weyburne, Emily S; Wilkins, Owen M; Sha, Zhe et al. (2017) Inhibition of the Proteasome ?2 Site Sensitizes Triple-Negative Breast Cancer Cells to ?5 Inhibitors and Suppresses Nrf1 Activation. Cell Chem Biol 24:218-230
VerPlank, Jordan J S; Goldberg, Alfred L (2017) Regulating protein breakdown through proteasome phosphorylation. Biochem J 474:3355-3371
Edison, Natalia; Curtz, Yael; Paland, Nicole et al. (2017) Degradation of Bcl-2 by XIAP and ARTS Promotes Apoptosis. Cell Rep 21:442-454
Volodin, Alexandra; Kosti, Idit; Goldberg, Alfred Lewis et al. (2017) Myofibril breakdown during atrophy is a delayed response requiring the transcription factor PAX4 and desmin depolymerization. Proc Natl Acad Sci U S A 114:E1375-E1384
Kuo, Chueh-Ling; Goldberg, Alfred Lewis (2017) Ubiquitinated proteins promote the association of proteasomes with the deubiquitinating enzyme Usp14 and the ubiquitin ligase Ube3c. Proc Natl Acad Sci U S A 114:E3404-E3413
Collins, Galen Andrew; Goldberg, Alfred L (2017) The Logic of the 26S Proteasome. Cell 169:792-806

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