Molecular probes for phosphotidylinositides utilizing heteroditopic synthetic receptors with turn-on fluorescence

Fluorescent probes were synthesized to bind to major phosphatidylinositol phosphate lipids (PIP_n) and other related anionic lipids, and the binding affinities between each probe and lipid type were studied. PIP_n lipids are usually found on the interior membranes in animal cells, and their localization within cells and dynamic changes in their distribution are the basis for many cell signaling events. It is also known that dysregulation of PIP_n levels is a feature of many diseases. Probes were designed with two types of anion recognition elements, with one having zinc(II)-dipicolylamine (ZnDPA) and the other having guanidinium. Both probes also had a boronic acid targeting group and environment-sensitive fluorescent dye that increased in fluorescence intensity when bound to the lipid membrane. ZnDPA, guanidinium, and control probes were synthesized and their fluorescence response upon addition of liposomes containing the lipid were studied. PS (phosphatidylserine), PI (phosphatidylinositol), PIP (phosphatidylinositol-4-phosphate), and PIP₂ (phosphatidylinositol-4,5-bisphosphate) were the anionic lipids tested in this study. Results showed that binding affinities were highest for PIP₂ in liposomes for both ZnDPA and guanidinium probes and lower for lipsomes containing other anionic lipids or the PC (zwitterionic) control. It was also shown that the guanidinium probe had the greatest increase in fluorescence intensity when binding to anionic lipids, but the ZnDPA probe had a much higher binding affinity.