QFRET-based counterscreen for inhibitors of PFM18AAP: biochemical high throughput dose response assay for inhibitors of the Cathepsin L proteinase (CTSL1).
Grant Proposal PI: John Dalton and Donald Gardiner, Queensland Institute of Medical Research, Australia ..more
Source (MLPCN Center Name): The Scripps Research Institute Molecular Screening Center
Affiliation: The Scripps Research Institute, TSRI
Assay Provider: John Dalton and Donald Gardiner, Queensland Institute of Medical Research, Australia
Network: Molecular Library Probe Production Centers Network (MLPCN)
Grant Proposal Number: 1 R03 MH084103-01
Grant Proposal PI: John Dalton and Donald Gardiner, Queensland Institute of Medical Research, Australia
External Assay ID: CTSL1_INH_QFRET_1536_3XIC50
Name: QFRET-based counterscreen for inhibitors of PFM18AAP: biochemical high throughput dose response assay for inhibitors of the Cathepsin L proteinase (CTSL1).
Aminopeptidases (APs) are metalloproteases that cleave amino-terminal (N-terminal) amino acids during protein synthesis (1, 2) . These enzymes are characterized in part by their post-translational removal of leucine, aspartate, proline, methionine, etc from proteins and peptides, in order that proteins are properly regulated, targeted for degradation, and trafficked within both animal and plant cells (3). As a result, these enzymes are involved in diverse processes, including meiosis (1), cellular senescence (1), blood pressure control (4, 5), angiogenesis (6), and inflammation (7). PFM18AAP is the sole aspartyl aminopeptidase (AAP) present in the genome of the malaria parasite Plasmodium falciparum (8). It exhibits exopeptidase activity exclusively against the N-terminal acidic amino acids glutamate and aspartate (9-11), is found in all intra-erythrocytic stages of the parasite (9), and functions to complete the hydrolysis of host hemoglobin into amino acids for use in de novo protein synthesis by the parasite (12, 13). Studies demonstrating that genetic knockdown of PFM18AAP results in a lethal parasite phenotype (9), and that inhibitors of methionine (14) and leucine (12, 15) aminopeptidases prevent malaria growth in culture and hemoglobin degradation, suggest that these enzymes are essential for parasite survival. As a result, the identification of selective inhibitors of PFM18AAP would elucidate this enzyme's role in the P. falciparum lifecycle, and serve as potential therapeutic agents to control malaria infection.
1. Walling, L.L., Recycling or regulation? The role of amino-terminal modifying enzymes. Curr Opin Plant Biol, 2006. 9(3): p. 227-33.
2. Meinnel, T., Serero, A., and Giglione, C., Impact of the N-terminal amino acid on targeted protein degradation. Biol Chem, 2006. 387(7): p. 839-51.
3. Jankiewicz, U. and Bielawski, W., The properties and functions of bacterial aminopeptidases. Acta Microbiol Pol, 2003. 52(3): p. 217-31.
4. Banegas, I., Prieto, I., Vives, F., Alba, F., de Gasparo, M., Segarra, A.B., Hermoso, F., Duran, R., and Ramirez, M., Brain aminopeptidases and hypertension. J Renin Angiotensin Aldosterone Syst, 2006. 7(3): p. 129-34.
5. Silveira, P.F., Gil, J., Casis, L., and Irazusta, J., Peptide metabolism and the control of body fluid homeostasis. Curr Med Chem Cardiovasc Hematol Agents, 2004. 2(3): p. 219-38.
6. Zhong, H. and Bowen, J.P., Antiangiogenesis drug design: multiple pathways targeting tumor vasculature. Curr Med Chem, 2006. 13(8): p. 849-62.
7. Proost, P., Struyf, S., and Van Damme, J., Natural post-translational modifications of chemokines. Biochem Soc Trans, 2006. 34(Pt 6): p. 997-1001.
8. Wilk, S., Wilk, E., and Magnusson, R.P., Purification, characterization, and cloning of a cytosolic aspartyl aminopeptidase. J Biol Chem, 1998. 273(26): p. 15961-70.
9. Teuscher, F., Lowther, J., Skinner-Adams, T.S., Spielmann, T., Dixon, M.W., Stack, C.M., Donnelly, S., Mucha, A., Kafarski, P., Vassiliou, S., Gardiner, D.L., Dalton, J.P., and Trenholme, K.R., The M18 aspartyl aminopeptidase of the human malaria parasite Plasmodium falciparum. J Biol Chem, 2007. 282(42): p. 30817-26.
10. Gyang, F.N., Poole, B., and Trager, W., Peptidases from Plasmodium falciparum cultured in vitro. Mol Biochem Parasitol, 1982. 5(4): p. 263-73.
11. Vander Jagt, D.L., Baack, B.R., and Hunsaker, L.A., Purification and characterization of an aminopeptidase from Plasmodium falciparum. Mol Biochem Parasitol, 1984. 10(1): p. 45-54.
12. Nankya-Kitaka, M.F., Curley, G.P., Gavigan, C.S., Bell, A., and Dalton, J.P., Plasmodium chabaudi chabaudi and P. falciparum: inhibition of aminopeptidase and parasite growth by bestatin and nitrobestatin. Parasitol Res, 1998. 84(6): p. 552-8.
13. Lauterbach, S.B. and Coetzer, T.L., The M18 aspartyl aminopeptidase of Plasmodium falciparum binds to human erythrocyte spectrin in vitro. Malar J, 2008. 7: p. 161.
14. Chen, X., Chong, C.R., Shi, L., Yoshimoto, T., Sullivan, D.J., Jr., and Liu, J.O., Inhibitors of Plasmodium falciparum methionine aminopeptidase 1b possess antimalarial activity. Proc Natl Acad Sci U S A, 2006. 103(39): p. 14548-53.
15. Stack, C.M., Lowther, J., Cunningham, E., Donnelly, S., Gardiner, D.L., Trenholme, K.R., Skinner-Adams, T.S., Teuscher, F., Grembecka, J., Mucha, A., Kafarski, P., Lua, L., Bell, A., and Dalton, J.P., Characterization of the Plasmodium falciparum M17 leucyl aminopeptidase. A protease involved in amino acid regulation with potential for antimalarial drug development. J Biol Chem, 2007. 282(3): p. 2069-80.
Keywords: Cathepsin L, CTSL1, cathepsin L1, CATL, MEP, PFM18AAP, M18AAP, malaria, parasite, plasmodium falciparum, exopeptidase, counterscreen, dose response, HTS, high throughput screen, 1536, inhibitor, inhibition, fluorescence, MCA, QFRET, FLINT, peptide, cleavage, Scripps, Scripps Florida, The Scripps Research Institute Molecular Screening Center, SRIMSC, Molecular Libraries Probe Production Centers Network, MLPCN.
The purpose of this counterscreen assay is to determine dose response curves for compounds identified as active in a set of previous experiments entitled, "QFRET-based biochemical high throughput confirmation assay for inhibitors of the Plasmodium falciparum M18 Aspartyl Aminopeptidase (PFM18AAP)" (AID 2178). In this biochemical assay, a commercially available fluorogenic peptide substrate (Z-Leu-Arg-MCA) is incubated with purified recombinant cathepsin L1 protein in the presence of test compounds. Cleavage of the substrate by cathepsin L1 releases the fluorogenic MCA leaving group, leading to an increase in well fluorescence. As designed, compounds that inhibit cathepsin L1 will prevent substrate cleavage and liberation of the fluorescent leaving group, resulting in decreased well fluorescence. Test compounds were assayed in triplicate in a 10-point 1:3 dilution series starting at a nominal test concentration of 59.6 micromolar.
Prior to the start of the assay, 2.5 microliters of assay buffer (25mM Tris HCl pH7.5, 1mM DTT, 0.1% BSA) containing 1.5micrograms/mL cathepsin L were dispensed into a 1536 microtiter plate. Next, 30 nL of test compound in DMSO, Z-Phe-Ala-diazomethylketone (1micromolar final concentration), or DMSO alone (0.59% final concentration) were added to the appropriate wells. The plates were then incubated for 30 minutes at 25 degrees Celsius.
The assay was started by dispensing 2.5 microliters of 100 micromolar Z-Leu-Arg-MCA substrate in buffer (25 mM Tris HCl, pH 7.5, 1mM DTT) into all wells. Well fluorescence was read immediately (T0) on the Viewlux (Perkin-Elmer) and again after 90 minutes (T90) of incubation at 25 degrees Celsius.
Prior to further calculations, T0 was subtracted from T90 for each individual well. The difference between RFU values read at T0 (RFU_T0) and T90 (RFU_T90), named delta RFU, was calculated as follows:
delta RFU = RFU_T90 - RFU_T0
The percent inhibition for each well was then calculated as follows:
Percent inhibition = ( test_compound_delta RFU - negative_control_delta RFU ) / ( positive_control_delta RFU - negative_control_delta RFU ) * 100
Test_Compound is defined as wells containing test compound.
Negative_Control is defined as the median of the wells containing Cathepsin L.
Positive_Control is defined as the median of the wells containing Z-Phe-Ala-diazomethylketone.
For each test compound, percent inhibition was plotted against compound concentration. A four parameter equation describing a sigmoidal dose-response curve was then fitted with adjustable baseline using Assay Explorer software (Symyx Technologies Inc). The reported IC50 values were generated from fitted curves by solving for the X-intercept value at the 50% inhibition level of the Y-intercept value. In cases where the highest concentration tested (i.e. 59.6 micromolar) did not result in greater than 50% inhibition, the IC50 was determined manually as greater than 59.6 micromolar. Compounds with an IC50 greater than 10 micromolar were considered inactive. Compounds with an IC50 equal to or less than 10 micromolar were considered active.
Any compound with a percent activity value <50% at all test concentrations was assigned an activity score of zero. Any compound with a percent activity value >50% at any test concentration was assigned an activity score greater than zero. Activity score was then ranked by the potency, with the most potent compounds assigned the highest activity scores.
There are no active compounds in this assay.
List of Reagents:
Cathepsin L enzyme (supplied by Assay Provider)
Z-Leu-Arg-MCA substrate (Peptides International, part MCA-3210-v)
1536-well plates (Greiner, part 789176)
Tris (Amresco, part 0497)
DTT (Invitrogen, part 15508-013)
Z-Phe-Ala-diazomethylketone (Bachem, part N-1040)
BSA (Calbiochem, part 126609)
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. In this assay, Z-Phe-Ala-diazomethylketone had an IC50 of approximately 5.2 nanomolar. 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. The MLSMR was not able to provide all compounds selected for testing in this AID.
* Activity Concentration. ** Test Concentration.
Data Table (Concise)