Ubiquitin is a protein modifier that plays a central role in cellular regulation and disease processes. It is covalently attached to proteins through an enzymatic cascade involving three classes of enzymes (E1, E2, E3 enzymes), with the E3s conferring target protein specificity. Among the several classes of E3 enzymes, HECT E3s are unique in that they function via a covalent enzyme-ubiquitin intermediate and participate directly in catalysis of ubiquitin conjugation. First discovered through studies on HPV-associated cervical cancer, HECT E3s also play important roles in other types of cancer, neurologic disease, various signaling pathways, and intracellular protein trafficking. One human HECT E3, Herc5, catalyzes conjugation of an interferon-induced ubiquitin-like modifier called ISG15, which is important in anti-viral responses. These diverse health-related functions highlight the importance of understanding the mechanism, function, and regulation of HECT E3s.
Aim 1 of this renewal application will focus on critical aspects of the biochemical mechanism of HECT E3s. A complete understanding of enzyme mechanism is critical for development of small molecules (drugs) that can either up- or down-regulate HECT E3 function in specific disease states. Importantly, very few natural targets of HECT E3s have been identified, and this has hampered our understanding of their biological functions.
In Aim 2, we will develop and implement a completely novel approach for HECT E3 substrate identification, based on the unique mechanism and structure of the catalytic domain.
Aim 3 represents a new research direction, where we have applied approaches developed in our ISG15 studies to analyze Co-Translational Ubiquitination (CTU), a phenomenon that has been linked to protein quality control, protein folding, and protein aggregation diseases. We will address the function of CTU through identification of target proteins and characterization of the enzymes of the pathway. We anticipate that these studies will have a strong and sustained impact on the many aspects of human health that are affected by the ubiquitin system, including cancer biology, cell signaling pathways, protein folding diseases, and infectious diseases.

Public Health Relevance

Ubiquitin is a protein modifier that plays a central role in virtually all cellular processes and pathways, as well as an incredible array of disease processes, including cancer, neurologic diseases, and infectious diseases. It is essential to characterize the biochemistry of the enzymes that selectively conjugate ubiquitin to target proteins in order to develop small molecules that can be used to modulate the system for therapeutic purposes.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
9R01GM103619-17
Application #
8401066
Study Section
Special Emphasis Panel (ZRG1-CB-R (02))
Program Officer
Gerratana, Barbara
Project Start
1996-12-13
Project End
2016-06-30
Budget Start
2012-07-06
Budget End
2013-06-30
Support Year
17
Fiscal Year
2012
Total Cost
$289,856
Indirect Cost
$89,856
Name
University of Texas Austin
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
170230239
City
Austin
State
TX
Country
United States
Zip Code
78712
Huibregtse, Jon M (2018) A proteasomal partner goes missing in Angelman syndrome. J Biol Chem 293:18400-18401
O'Connor, Hazel F; Huibregtse, Jon M (2017) Enzyme-substrate relationships in the ubiquitin system: approaches for identifying substrates of ubiquitin ligases. Cell Mol Life Sci 74:3363-3375
Wang, Feng; Canadeo, Larissa A; Huibregtse, Jon M (2015) Ubiquitination of newly synthesized proteins at the ribosome. Biochimie 114:127-33
O'Connor, Hazel F; Lyon, Nancy; Leung, Justin W et al. (2015) Ubiquitin-Activated Interaction Traps (UBAITs) identify E3 ligase binding partners. EMBO Rep 16:1699-712
Wang, Feng; Durfee, Larissa A; Huibregtse, Jon M (2013) A cotranslational ubiquitination pathway for quality control of misfolded proteins. Mol Cell 50:368-78