Development of a high-throughput fluorescence polarization assay for Bcl-x(L).
Antiapoptotic protein Bcl-x(L) has been demonstrated to play a very important role in a variety of diseases such as cancer. Its biological function can be inhibited by proapoptotic proteins such Bak, Bad, and Bax by forming complexes mediated primarily by the Bcl-2 homology 3 (BH3) domain. To facilitate drug discovery for Bcl-x(L) inhibitors, we have developed and optimized a fluorescence polarization assay based on the interaction between Bcl-x(L) and BH3 domain peptides. We observed that the fluorescein-labeled Bad BH3 peptide [NLWAAQRYGRELRRMSDK(fluorescein)FVD or fluorescent Bad peptide] generates best overall results. Fluorescent Bad peptide interacts strongly with Bcl-x(L) with a K(d) of 21.48nM. The assay is stable over a 24-h period and can tolerate the presence of dimethyl sulfoxide up to 8%. By using a competition assay, several peptides derived from the BH3 region of Bak, Bad, Bax, and Bcl-2 were investigated. Bad and Bak BH3 peptides compete efficiently with IC(50) values of 0.048 and 1.14 microM, respectively, while the peptides from the BH3 region of Bcl-2 and Bax compete weakly. A mutated Bak peptide, which has been shown to be inactive for binding to Bcl-x(L), did not compete. The relative binding order of the peptides (Bad>Bak>Bcl-2>Bax>mutated Bak) correlates well with previously published results. When tested in high-throughput formats, the assay has a signal-to-noise ratio of 15.37 and a Z(') factor of at least 0.73. The plate-to-plate variability for free peptide control and bound peptide control is minimal. This validates the assay not only for investigating the nature of Bcl-x(L)-peptide interaction, but also for high-throughput screening of Bcl-x(L) inhibitors.
Department 4N6, Cancer Research, Pharmaceutical Products Division, Abbott Laboratories, Abbott Park, IL 60064, USA. haichao.zhang@abbott.com
Haichao
H
Zhang
Paul
P
Nimmer
Saul H
SH
Rosenberg
Shi-Chung
SC
Ng
Mary
M
Joseph
D001667:Binding, Competitive; D002352:Carrier Proteins / Q000032:analysis; D005454:Fluorescence Polarization / Q000379:methods*; D005456:Fluorescent Dyes; D006801:Humans; D009154:Mutation; D010446:Peptide Fragments / Q000737:chemistry; D011518:Proto-Oncogene Proteins / Q000032:analysis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis*; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein
C494819:BAD protein, human; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D002352:Carrier Proteins; D005456:Fluorescent Dyes; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein