Confirmation Assay for Inhibitors of Ubiquitin-specific Protease USP2a Using CHOP2 as the Reporter
Homeostasis of cellular proteins is maintained through a combination of synthesis and degradation. The pathway that accounts for the majority of protein degradation is the ubiquitin-proteasomal pathway. Ubiquitin (Ub) is highly conserved in all cells and the generation of a multi-Ub chain typically targets proteins for degradation by the proteasome. However, ubiquitination is highly reversible more ..
BioActive Compounds: 93
NIH Molecular Libraries Probe Centers Network [MLPCN]
NIH Chemical Genomics Center [NCGC]
MLSCN Grant: XO1-MH079852-01
PI Name: Nicholson, Ben. Progenra Inc, Malvern, PA
NCGC Assay Overview:
Homeostasis of cellular proteins is maintained through a combination of synthesis and degradation. The pathway that accounts for the majority of protein degradation is the ubiquitin-proteasomal pathway. Ubiquitin (Ub) is highly conserved in all cells and the generation of a multi-Ub chain typically targets proteins for degradation by the proteasome. However, ubiquitination is highly reversible and dynamic. Deubiquitination, the reverse process, is catalyzed through the action of enzymes referred to as isopeptidases or deubiquitinating enzymes (DUBs) [1, 2]. This group of enzymes is collectively responsible for maintaining adequate pools of free ubiquitin and regulating the ubiquitination status of cellular proteins. The class of DUBs referred to as the ubiquitin-specific proteases (USP) family functions endoproteolytically to cleave Ub chains from a wide range of protein substrates. USP2a deubiquitinates fatty acid synthase (FASN) which has recently been identified as an emerging oncology target. To identify inhibitors of USP2a a cell-free assay was employed.
This assay takes advantage of attaching an Ub to a reporter enzyme, rendering the reporter catalytically inactive. The reporter enzyme chosen is an enterokinase called CHOP2, which is activated when the Ub is cleaved by USP2. The free and now activated reporter can subsequently act on its reporter substrate. Thus, this coupled assay gives a fluorescent read-out at excitation/emission wavelengths of 485/531. The assay was developed by Progenra, Inc. and has been licensed for sale by LifeSensors, Inc. as Ub-CHOP2-Reporter-Kit (#PR1101).
NCGC Assay Protocol Summary:
The assay buffer, prepared fresh at the day of the assay, contains 20mM Tris-HCl pH 8.0, 2mM CaCl2, 2mM beta-Mercaptoethanol, 0.05% CHAPS. 3ul of 20nM (10nM final) USP2 core, which is stored on ice, is dispensed into a medium-binding black solid Kalypsys 1,536 well plate using the Kalypsys dispenser. The assay plate is then pinned with 23nL compound with the Kalypsys pintool in columns 5-48. The controls are pinned as follows: column 1 two-fold dilutions of 2M NEM in duplicate; column 2 2M NEM (final concentration 38.2mM); column 3&4 DMSO. The assay plate is incubated at RT for 30min. Subsequently, 1.5uL of 100nM (25nM final) Ub-CHOP2 and 1.5uL of 100nM (25nM final) Reporter Substrate (both stored on ice and protected from light) were dispensed into the plate using the Kalypsys dispenser. Plates were read after 60min RT incubation on a ViewLux (Perkin Elmer) plate reader using the following wavelengths Ex 485nm /Em 531nm.
Data were normalized to the to AC100 inhibition (NEM). Concentration-response curves were fitted to the normalized data and the concentration-response curves were then classified based on curve quality (r2), response magnitude and degree of measured activity. The time zero reading was used to flag fluorescence artifacts.
Keywords: ubiquitination, deubiquitination, proteases, profluorescent, MLSMR, MLPCN, NIH Roadmap, qHTS, NCGC
1. Compounds are first classified as having full titration curves, partial modulation, partial curve (weaker actives), single point activity (at highest concentration only), or inactive. See data field "Curve Description". For this assay, apparent inhibitors are ranked higher than compounds that showed apparent activation.
2. For all inactive compounds, PUBCHEM_ACTIVITY_SCORE is 0. For all active compounds, a score range was given for each curve class type given above. Active compounds have PUBCHEM_ACTIVITY_SCORE between 40 and 100. Inconclusive compounds have PUBCHEM_ACTIVITY_SCORE between 1 and 39. Fit_LogAC50 was used for determining relative score and was scaled to each curve class' score range.
Categorized Comment - additional comments and annotations
* Activity Concentration. ** Test Concentration.
Data Table (Concise)