External ID: TBREL1_INH_FRET_1536_1X%INH PRUN
Protocol:
Assay Overview:
The purpose of this biochemical assay is to identify compounds that act as inhibitors of Trypanosoma brucei RNA editing ligase 1 (TbREL1). In this assay, REL1 enzyme is incubated with test compounds and fluorescently labeled RNA substrates. The assay substrate consists of a pair of RNA oligonucleotides, one with the FRET donor (6-FAM) and the other with FRET acceptor (CY5), which are annealed to a complementary strand. Uninhibited REL-1, in the presence of ATP, will ligate the RNA oligos with the FRET pair. STOP buffer is then added which denatures the annealed substrate and disrupts any unligated FRET pairings. As designed, test compounds that act as REL1 inhibitors in the presence of ATP will prevent ligation of the RNA oligos with the FRET pair, thereby leading to decreasing well FRET signal. Compounds are tested in singlicate at a nominal test concentration of 9.66 micromolar.
Protocol Summary:
Prior to the start of the assay, 2 microliters of annealed RNA substrate mix in annealing buffer (25mM KCl, 12.5mM Tris pH8.0, 5mM Magnesium acetate and 0.25mM DTT) in the presence of ATP (10uM final concentration) was dispensed into all wells of 1536 microtiter plates. Next, 39 nL of test compound in DMSO, NSC42067 (96uM final concentration) in DMSO, or DMSO alone (0.97% final concentration) were added to the appropriate wells. The assay was started by dispensing 2 microliters of ligation buffer (5mM KCl, 12.5mM Tris pH 6.0, 1mM Magnesium acetate, 0.25mM DTT, 0.2% Triton X-100 and 0.0003% Brij 35) into columns 1 thru column 3 and 2 microliters of ligation buffer containing REL1 enzyme (3.13ug/mL final concentration) into columns 4 thru 48. Plates were centrifuged and incubated for 30 minutes at 25 degrees Celsius.
STOP Buffer (8M UREA and 10mM EDTA pH8.0) was dispensed into all wells to disrupt non-ligated RNA substrates. Plates were centrifuged and after 15 minutes of incubation at 25 degrees Celsius, fluorescence was read on a Viewlux microplate reader (PerkinElmer, Turku, Finland) using a FITC dichroic mirror (excitation = 480nm, emission = 671nm).
The percent inhibition for each compound was calculated as follows:
100 * ( ( Test_Compound - Median_Low_Control ) / ( Median_High_Control - Median_Low_Control ) )
Where:
Test_Compound is defined as wells containing REL1 enzyme in the presence of test compound and RNA substrate.
High_Control is defined as wells containing REL1 enzyme, NSC42067 and RNA substrate.
Low_Control is defined as the median of the wells containing test compounds.
PubChem Activity Outcome and Score:
A mathematical algorithm was used to determine nominally inhibiting compounds in the primary screen. Two values were calculated: (1) the average percent inhibition of all compounds tested, and (2) three times their standard deviation. The sum of these two values was used as a cutoff parameter, i.e. any compound that exhibited greater % inhibition than the cutoff parameter was declared active.
The reported PubChem Activity Score has been normalized to 100% observed primary inhibition. Negative % inhibition values are reported as activity score zero.
The activity score range for active compounds is 100-11, for inactive 10-0.
List of Reagents:
REL1 enzyme (supplied by Assay Provider)
Pre-annealed RNA substrate mix (supplied by Assay Provider)
NSC 42067 (Positive Control-NCI/NIH Development Therapeutics Program, part 42067)
KCl (Sigma, part P9333)
Magnesium acetate (Sigma, part M0631)
Tris (Amresco, part 0497)
ATP (Sigma, part A6559)
DTT (Fisher, part BP172)
Triton X-100 (Sigma, part T9284)
Brij35 (Pierce, part 20150)
EDTA (Fisher, part BP2482)
UREA (Sigma, part 51456)
1536-well plates (Greiner, part 789176)
Comment:
Due to the increasing size of the MLPCN compound library, this assay may have been run as two or more separate campaigns, each campaign testing a unique set of compounds. All data reported were normalized on a per-plate basis. Possible artifacts of this assay can include, but are not limited to: dust or lint located in or on wells of the microtiter plate, compounds that modulate well fluorescence. All test compound concentrations reported above and below are nominal; the specific test concentration(s) for a particular compound may vary based upon the actual sample provided by the MLSMR.