HTRF FRET Assay: A homogeneous time-resolved FRET assay was used to determine IC50 values for inhibitors of the soluble human BACE1 catalytic domain. This assay monitored the increase of 620 nm fluorescence that resulted from BACE1 cleavage of an APPswedish APPswe mutant peptide FRET substrate (QSY7-EISEVNLDAEFC-Europium-amide). This substrate contained an N-terminal QSY7 moiety that served as a quencher of the C-terminal Europium fluorophore (620 nm Em). In the absence of enzyme activity, 620 nm fluorescence was low in the assay and increased linearly over 3 hours in the presence of uninhibited BACE1 enzyme. Inhibition of BACE1 cleavage of the QSY7-APPswe-Eu substrate by inhibitors was manifested as a suppression of 620 nm fluorescence.Varying concentrations of inhibitors at 3x the final desired concentration in a volume of 10 ul were preincubated with purified human BACE1 catalytic domain (3 nM in 10 ul) for 30 minutes at 30 C. in reaction buffer containing 20 mM Na-Acetate pH 5.0.
Homogeneous Time-Resolved FRET Assay: The protocol that was used to determine the recited values isdescribed as follows.BACE1 HTRF FRET AssayReagentsNa+-Acetate pH 5.01% Brij-35GlycerolDimethyl Sulfoxide (DMSO)Recombinant human soluble BACE1 catalytic domain (>95% pure)APP Swedish mutant peptide substrate (QSY7-APPswe-Eu):QSY7-EISEVNLDAEFC-Europium-amideA homogeneous time-resolved FRET assay was used to determine IC50 values for inhibitors of the soluble human BACE1 catalytic domain. This assay monitored the increase of 620 nm fluorescence that resulted from BACE1 cleavage of an APPswedish APPswe mutant peptide FRET substrate (QSY7-EISEVNLDAEFC-Europium-amide). This substrate contained an N-terminal QSY7 moiety that served as a quencher of the C-terminal Europium fluorophore (620 nm Em). In the absence of enzyme activity, 620 nm fluorescence was low in the assay and increased linearly over 3 hours in the presence of uninhibited BACE1 enzyme.
HTRF assay: Inhibitor IC50s at purified human autoBACE-2 were determined in a time-resolved endpoint proteolysis assay that measures hydrolysis of the QSY7-EISEVNLDAEFC-Eu-amide FRET peptide substrate (BACE-HTRF assay). BACE-mediated hydrolysis of this peptide results in an increase in relative fluorescence (RFU) at 620 nm after excitation with 320 nm light. Inhibitor compounds, prepared at 3x the desired final concentration in 1xBACE assay buffer (20 mM sodium acetate pH 5.0, 10% glycerol, 0.1% Brij-35) supplemented with 7.5% DMSO were pre-incubated with an equal volume of autoBACE-2 enzyme diluted in 1xBACE assay buffer (final enzyme concentration 1 nM) in black 384-well NUNC plates for 30 minutes at 30 C. The assay was initiated by addition of an equal volume of the QSY7-EISEVNLDAEFC-Eu-amide substrate (200 nM final concentration, Km=8 uM for 4 uM for autoBACE-2) prepared in 1xBACE assay buffer supplemented with 7.5% DMSO and incubated for 90 minutes at 30 C.
HTRF FRET Assay: Inhibitor IC50s at purified human autoBACE-2 were determined in a time-resolved endpoint proteolysis assay that measures hydrolysis of the QSY7-EISEVNLDAEFC-Eu-amide FRET peptide substrate (BACE-HTRF assay). BACE-mediated hydrolysis of this peptide results in an increase in relative fluorescence (RFU) at 620 nm after excitation with 320 nm light. Inhibitor compounds, prepared at 3x the desired final concentration in 1xBACE assay buffer (20 mM sodium acetate pH 5.0, 10% glycerol, 0.1% Brij-35) supplemented with 7.5% DMSO were pre-incubated with an equal volume of autoBACE-2 enzyme diluted in 1xBACE assay buffer (final enzyme concentration 1 nM) in black 384-well NUNC plates for 30 minutes at 30 C. The assay was initiated by addition of an equal volume of the QSY7-EISEVNLDAEFC-Eu-amide substrate (200 nM final concentration, Km=8 M for 4 M for autoBACE-2) prepared in 1xBACE assay buffer supplemented with 7.5% DMSO and incubated for 90 minutes at 30 C.