A high throughput fluorescence polarization assay for inhibitors of the GoLoco motif/G-alpha interaction.

Methods Development

Abstract

The GoLoco motif is a short Galpha-binding polypeptide sequence. It is often found in proteins that regulate cell-surface receptor signaling, such as RGS12, as well as in proteins that regulate mitotic spindle orientation and force generation during cell division, such as GPSM2/LGN. Here, we describe a high throughput fluorescence polarization (FP) assay using fluorophore-labeled GoLoco motif peptides for identifying inhibitors of the GoLoco motif interaction with the G-protein alpha subunit Galpha (i1). The assay exhibits considerable stability over time and is tolerant to DMSO up to 5%. The Z'-factors for robustness of the GPSM2 and RGS12 GoLoco motif assays in a 96-well plate format were determined to be 0.81 and 0.84, respectively; the latter assay was run in a 384-well plate format and produced a Z'-factor of 0.80. To determine the screening factor window (Z-factor) of the RGS12 GoLoco motif screen using a small molecule library, the NCI Diversity Set was screened. The Z-factor was determined to be 0.66, suggesting that this FP assay would perform well when developed for 1,536-well format and scaled up to larger libraries. We then miniaturized to a 4 microL final volume a pair of FP assays utilizing fluorescein- (green) and rhodamine- (red) labeled RGS12 GoLoco motif peptides. In a fully-automated run, the Sigma-Aldrich LOPAC(1280) collection was screened three times with every library compound being tested over a range of concentrations following the quantitative high throughput screening (qHTS) paradigm; excellent assay performance was noted with average Z-factors of 0.84 and 0.66 for the green- and red-label assays, respectively.

Authors

Kimple, Adam J; Yasgar, Adam; Hughes, Mark; Jadhav, Ajit; Willard, Francis S; Muller, Robin E; Austin, Christopher; Inglese, James; Ibeanu, Gordon C; Siderovski, David P; Simeonov, Anton;

Keywords

  • Amino Acid Motifs
  • Biological Assay/ methods
  • Fluorescence Polarization/ methods
  • GTP Phosphohydrolase Activators/ metabolism
  • GTP-Binding Protein alpha Subunits, Gi-Go/ analysis
  • GTP-Binding Protein alpha Subunits, Gi-Go/ antagonists & inhibitors
  • GTP-Binding Protein alpha Subunits, Gi-Go/ metabolism
  • Humans
  • Models, Molecular
  • Molecular Sequence Data
  • RGS Proteins/ metabolism
  • Staining and Labeling

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