FIGURE 5.
The aPIIQGAP1 and PH domain of GRP1 share a preference for PtdInsP3 over Ins(1,3,4,5)P4. The concentration dependence with which aPIIQGAP1 (A and C) and the PH domain of GRP1 (B and D) bind to PtdInsP3 (closed circles) or Ins(1,3,4,5)P4 (open triangles) is compared using a competition TR-FRET assay. Binding was measured by the reduction in the optimal FRET signal resulting from the introduction the free ligand indicated to FRET complexes pre-established with biotinylated PtdInsP3 (2.5 pmol, A and B) or biotinylated Ins(1,3,4,5)P4 (3.0 pmol; C and D). The data indicate the mean ± the range of duplicate measurements from a single experiment representative of two that gave similar results. Curves were fitted as described in the legend for Fig. 2C.