Structural changes in profilin accompany its binding to phosphatidylinositol 4,5-bisphosphate

The effect on the structure of profilin of phosphatidylinositol 4,5-bisphosphate (PIP 2) binding was probed by fluorescence and circular dichroism (CD) spectroscopy, Fluorescence of Trp 3 and Trp 31 of profilin at 292 nm showed a linear decrease in solution emission at 340 nm as PIP 2/profilin was increased from 0 to 80:1, apparently due to a static quenching mechanism involving formation of a nonfluorescent PIP 2/profilin complex. CD spectra revealed an increase of up to 3.3-fold in the molar ellipticity at 222 nm for profilin as it binds PIP 2, as well as changes in the Cotton effect between 250 and 310 nm. These results are consistent with a possible increase in the α-helix content or profilin triggered by the binding or PIP 2.