THE MAMMALIAN PROFILIN ISOFORMS DISPLAY COMPLEMENTARY AFFINITIES FOR PIP2 AND PROLINE-RICH SEQUENCES

We present a study on the binding properties of the bovine profilin is oforms to both phosphatidylinositol 4,5-bisphosphate (PIP2) and prolin e-rich peptides derived from vasodilator-stimulated phosphoprotein (VA SP) and cyclase-assaeiated protein (CAP), Using microfiltration, we sh ow that compared with profilin II, profilin I has a higher affinity fo r PIP2. On the other hand, fluorescence spectroscopy reveals that prol ine-rich peptides bind better to profilin II. At micromolar concentrat ions, profilin II dimerizes upon binding to proline-rich peptides. Cir cular dichroism measurements of profilin II reveal a significant confo rmational change in this protein upon binding of the peptide, We show further that PIP2 effectively competes for binding of profilin I to po ly-L-proline, since this isoform, but not profilin II, can be eluted f rom a poly-L-proline column with PIP2. Using affinity chromatography o n either profilin isoform, me identified profilin II as the preferred ligand for VASP in bovine brain extracts, The complementary affinities of the profilin isoforms for PIP2 and the proline-rich peptides offer the cell an opportunity to direct actin assembly at different subcell ular localizations through the same or different signal transduction p athways.