Direct measurement of PIP2 densities in biological membranes using a peptide-based sensor

Organization and composition of the plasma membrane are important modulators of many cellular programs. Phosphatidylinositol phosphate (PIP) lipids are low abundance membrane constituents with different arrangements of phosphate groups around an inositol head group that regulate a large number of signaling pathways. Many strategies have been developed to detect and track PIP species to monitor their clustering, mobility, and interaction with binding partners. We implement a peptide-based ratiometric sensor for the detection of PI(4,5)P2 lipids in reconstituted membrane systems that permit absolute quantification of PI(4,5)P2 densities down to physiological levels. The sensor is membrane permeable and easily applicable to measurements in living cells. Application of calibrated sensors to cells expressing common mutations in the small GTPase, Ras, showed a reshaping of surface PI(4,5)P2 levels and distributions in a mutation-specific manner. The rapid implementation of this quantitative sensing strategy to cellular studies of cellular signaling, membrane organization and dynamics should be broadly applicable.