Antimalarial activity against chloroquine and pyrimethamine-resistant Plasmodium falciparum Dd2 infected in RBV after 48 hrs by SYBR Green I-based fluorescence method
Fluorescence Resonance Energy Transfer (FRET) Assay : The recombinant human BACE1, Cathepsin D, and Cathepsin E enzymes were purchased from R&D Systems (catalog numbers are 931-AS, 1014AS and 1294AS, respectively). The enzymatic inhibition activity assays were determined using the fluorescence resonance energy transfer (FRET) assay. The assays were performed in a 384-well plate format. The recombinant human BACE-1 enzyme (R&D Systems, catalog#931-AS) was diluted to 20 ng/μL in assay buffer (100 mM sodium acetate pH 4.0), 10 point 1:3 serial dilutions of compound in DMSO were preincubated with the enzyme for 15 min at room temperature. The concentration of Cathepsin D was 20 ng/μL, and 1 ng/μL of Cathepsin E was used. CatD and CatE were activated by incubation in assay buffer (0.1 M NaOAc, 0.2 M NaCl, pH 3.5) at room temperature for 30 min. Subsequently, the rhBACE-1 substrate (R&D Systems, catalog# ES004), the Cathepsin D and Cathepsin E substrate (R&D Systems, Catalog # ES001) were added accordingly to final concentration
Enzyme Inhibition Assay : Plasmepsin-2 (PM-2; Plm II) and Plasmepsin (PM-4; Plm IV) expression and purification was performed following the published protocols (Istvan E S and Goldberg D E, 2005). The final purified protein was activated by diluting the protein to 0.3 mg/mL in activating buffer (0.1 M citrate pH 4.5, 0.1% Tween-20, 50 mM dithiothreitol) and incubated at room temperature for 40 min, then the activated enzyme was diluted in assay buffer (50 mM sodium acetate pH 4.7, 0.01% Tween-20). The enzymatic inhibition reaction was performed in 384 well plates with a total volume of 20 μl. 10 μl of diluted PM-2 or PM-4 enzyme was added to the 384-well plate except blank wells (blank wells add 10 μL of assay buffer) and 20 nL of serials of diluted 1000× compounds were added to the wells with 520 Echo® Liquid Handling System (Labcyte Inc.). 10 μL PM-2 peptide substrate (AnaSpec, Cat#, 62050) with assay buffer was then added to final concentration of 20 μM to start the reaction.
Enzyme Inhibition Assay : Plasmepsin-2 (PM-2; Plm II) and Plasmepsin (PM-4; Plm IV) expression and purification was performed following the published protocols (Istvan E S and Goldberg D E, 2005). The final purified protein was activated by diluting the protein to 0.3 mg/mL in activating buffer (0.1 M citrate pH 4.5, 0.1% Tween-20, 50 mM dithiothreitol) and incubated at room temperature for 40 min, then the activated enzyme was diluted in assay buffer (50 mM sodium acetate pH 4.7, 0.01% Tween-20). The enzymatic inhibition reaction was performed in 384 well plates with a total volume of 20 μl. 10 μl of diluted PM-2 or PM-4 enzyme was added to the 384-well plate except blank wells (blank wells add 10 μL of assay buffer) and 20 nL of serials of diluted 1000× compounds were added to the wells with 520 Echo® Liquid Handling System (Labcyte Inc.). 10 μL PM-2 peptide substrate (AnaSpec, Cat#, 62050) with assay buffer was then added to final concentration of 20 μM to start the reaction.
Fluorescence Resonance Energy Transfer (FRET) Assay : The recombinant human BACE1, Cathepsin D, and Cathepsin E enzymes were purchased from R&D Systems (catalog numbers are 931-AS, 1014AS and 1294AS, respectively). The enzymatic inhibition activity assays were determined using the fluorescence resonance energy transfer (FRET) assay. The assays were performed in a 384-well plate format. The recombinant human BACE-1 enzyme (R&D Systems, catalog#931-AS) was diluted to 20 ng/μL in assay buffer (100 mM sodium acetate pH 4.0), 10 point 1:3 serial dilutions of compound in DMSO were preincubated with the enzyme for 15 min at room temperature. The concentration of Cathepsin D was 20 ng/μL, and 1 ng/μL of Cathepsin E was used. CatD and CatE were activated by incubation in assay buffer (0.1 M NaOAc, 0.2 M NaCl, pH 3.5) at room temperature for 30 min. Subsequently, the rhBACE-1 substrate (R&D Systems, catalog# ES004), the Cathepsin D and Cathepsin E substrate (R&D Systems, Catalog # ES001) were added accordingly to final concentration
Fluorescence Resonance Energy Transfer (FRET) Assay : The recombinant human BACE1, Cathepsin D, and Cathepsin E enzymes were purchased from R&D Systems (catalog numbers are 931-AS, 1014AS and 1294AS, respectively). The enzymatic inhibition activity assays were determined using the fluorescence resonance energy transfer (FRET) assay. The assays were performed in a 384-well plate format. The recombinant human BACE-1 enzyme (R&D Systems, catalog#931-AS) was diluted to 20 ng/μL in assay buffer (100 mM sodium acetate pH 4.0), 10 point 1:3 serial dilutions of compound in DMSO were preincubated with the enzyme for 15 min at room temperature. The concentration of Cathepsin D was 20 ng/μL, and 1 ng/μL of Cathepsin E was used. CatD and CatE were activated by incubation in assay buffer (0.1 M NaOAc, 0.2 M NaCl, pH 3.5) at room temperature for 30 min. Subsequently, the rhBACE-1 substrate (R&D Systems, catalog# ES004), the Cathepsin D and Cathepsin E substrate (R&D Systems, Catalog # ES001) were added accordingly to final concentration