Counterscreen for inhibitors of the fructose-bisphosphate aldolase (FBA) of M. tuberculosis: Absorbance-based biochemical high throughput Glycerophosphate Dehydrogenase-Triosephosphate Isomerase (GDH-TPI) full deck assay to identify assay artifacts
Name: Counterscreen for inhibitors of the fructose-bisphosphate aldolase (FBA) of M. tuberculosis: Absorbance-based biochemical high throughput Glycerophosphate Dehydrogenase-Triosephosphate Isomerase (GDH-TPI) full deck assay to identify assay artifacts. ..more
BioActive Compounds: 4453
Source (MLPCN Center Name): The Scripps Research Institute Molecular Screening Center (SRISMC)
Center Affiliation: The Scripps Research Institute, TSRI
Assay Provider: Mary Jackson, Colorado State
Network: Molecular Library Probe Production Center Network (MLPCN)
Grant Proposal Number: 1 R21 NS066438-01
Grant Proposal PI: Mary Jackson, Colorado State
External Assay ID: GDH-TPI_INH_ABS_1536_1X%INH CSRUN
Name: Counterscreen for inhibitors of the fructose-bisphosphate aldolase (FBA) of M. tuberculosis: Absorbance-based biochemical high throughput Glycerophosphate Dehydrogenase-Triosephosphate Isomerase (GDH-TPI) full deck assay to identify assay artifacts.
The rise in antibiotic-resistant Mycobacterium tuberculosis and the lack of drugs capable of efficiently eradicating persistent bacilli responsible for life-long infections in humans emphasize the need for novel anti-TB agents with mechanisms of action different from those of existing drugs(1, 2). In fact, the latent form of Mycobacterium tuberculosis infects approximately a third of the global population (3). Class II fructose-1, 6-bisphosphate aldolase (FBA) is a key enzyme of glycolysis/gluconeogenesis induced in M. tuberculosis grown under oxygen-limiting conditions thought to mimic the physical microenvironment encountered by persistent bacilli in pulmonary lesions. Fructose bisphosphate aldolase (FBA) catalyzes the conversion of fructose bisphosphate into glyceraldehyde phosphate and dihydroxyacetone phosphate in a reversible fashion. As a result, this enzyme is a likely target for molecular tools to kill multi-drug-resistant as well as persistent M. tuberculosis (2).
Selective inhibition of FBA is expected to prevent M. tuberculosis from growing on host-derived fatty acids during persistent infection. Although ubiquitous in living organisms, FBAs can be divided into two classes which differ in their structure and reaction mechanism. While class I FBAs are the only type found in mammals, prokaryotes produce class II FBAs. The absence of class II FBAs from mammalian cells and the specificity of their structure and catalytic mechanism should make it possible to design specific inhibitors of class II enzymes that target pathogenic bacteria without affecting the host's gluconeogenetic and glycolytic pathways.
1. Siegel, R.E., Emerging gram-negative antibiotic resistance: daunting challenges, declining sensitivities, and dire consequences. Respir Care, 2008. 53(4): p. 471-9.
2. Fonvielle, M., M. Coincon, R. Daher, N. Desbenoit, K. Kosieradzka, N. Barilone, B. Gicquel, J. Sygusch, M. Jackson, and M. Therisod, Synthesis and biochemical evaluation of selective inhibitors of class II fructose bisphosphate aldolases: towards new synthetic antibiotics. Chemistry, 2008. 14(28): p. 8521-9.
3. Pegan, S.D., K. Rukseree, S.G. Franzblau, and A.D. Mesecar, Structural basis for catalysis of a tetrameric class IIa fructose 1,6-bisphosphate aldolase from Mycobacterium tuberculosis. J Mol Biol, 2009. 386(4): p. 1038-53.
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The purpose of this biochemical counterscreen is to determine whether compounds act as absorbance assay artifacts or are non-selective. This assay also serves as a counterscreen for a set of ongoing high throughput primary experiments entitled, "Absorbance-based biochemical primary high throughput screening assay to identify inhibitors of the aldolase of M. tuberculosis."
This counterscreen is similar in format to the aforementioned assay with the only two following differences: (i) the fructose-1,6-bisphosphate substrate is replaced with glyceraldehyde 3 phosphate, a product of its conversion by FBA and (ii) no (FBA) is used. The counterscreen hence recapitulates the two steps involved in the monitoring of FBA activity through the conversion of FB into the triose product glyceraldehyde 3 phosphate (G3P), which would be converted to dihydroxyacetone phosphate (DHAP) by the helper enzyme triose phosphate isomerase (TPI). A second helper enzyme, glycerophosphate dehydrogenase (GDH), converts the dihydroxyacetone phosphate to glycerol-3-phosphate with the concomitant oxidation of NADH to NAD, which is monitored by measuring the absorbance at 340 nm. In this new assay format, the A340 is independent of FBA activity, hence compounds that reduce absorbance at 340 nm are either absorbance artifacts or helper enzyme inhibitors that will not be pursued. Compounds are tested in singlicate at a final nominal concentration of 4.78 uM.
Prior to the start of the assay, 5 uL /well of Buffer A (50 mM HEPES, 0.01% Triton X-100, 10% Glycerol, pH8.0) supplemented with 400 nM ZnCl2,240 uM NADH and the helper enzymes GDH-TPI (4 U/mL) was dispensed into all wells of a 1536-well plate except the "No enzyme" wells that contained the same supplemented buffer but no GDH-TPI enzymes. Next, 48 nL of test compounds were then delivered in each well using a PinTool. The assay was then initiated by dispensing 5 uL of Buffer A supplemented with 240 uM of the substrate glyceraldehyde-3-phosphate (G3P). Plates were incubated at room temperature for 20 minutes before A340 was measured using the EnVision plate reader (Perkin Elmer).
The percent inhibition for each compound was calculated as follows:
%Inhibition = 100 * ( ( Test_Compound - Median_Low_Control ) / ( Median_High_Control - Median_Low_Control ) )
Test_Compound is defined as wells treated with test compounds.
Low_Control is defined as wells treated with DMSO.
High_Control is defined as wells with no GDH-TPI enzyme.
A mathematical algorithm was used to determine nominally inhibiting compounds in the primary screen. Two values were calculated for each assay plate: (1) the average percent inhibition of test compound wells and (2) three times their standard deviation. The sum of these two values was used as a cutoff parameter for each plate, i.e. any compound that exhibited greater % inhibition than the cutoff parameter was declared active.
PubChem Activity Outcome and Score:
The reported PubChem Activity Score has been normalized to 100% observed inhibition. Negative % inhibition values are reported as activity score zero.
The PubChem Activity Score range for active compounds is 100-13, and for inactive compounds 13-0.
List of Reagents:
ZnCl2 (Fisher Scientific, part Z33-500)
NADH (EMD Biosciences, part 481913)
GDH-TPI (Sigma, part G1881)
HEPES (EMD Biosciences, part EM-5310)
Triton X-100 (Sigma, part T8787)
Glycerol (Fisher, part AC327255000)
Glyceraldehyde-3-phosphate (Sigma, part D7137)
1536-well plates (Aurora, part 1091-11020-S)
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. In this case the results of each separate campaign were assigned "Active/Inactive" status based upon that campaign's specific compound activity cutoff value. 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, and compounds that quench or emit absorbance within the well. All test compound concentrations reported are nominal; the specific concentration for a particular test compound may vary based upon the actual sample provided by the MLSMR
Categorized Comment - additional comments and annotations
** Test Concentration.
Data Table (Concise)