Actin-regulating proteins such as profilin, gelsolin and CapG display unique ability to bind phosphoinositides in vitro, and have been suggested to play a role in the regulation of transmembrane signal transduction. In this study, we examined the binding affinity between these actin-binding proteins and various phosphoinositides including PtdIns(3,4,5)P3, PtdIns(3,4)P2, and PtdIns(4,5)P2 by gel filtration and fluorescence titration analyses. It was found that profilin, gelsolin, and CapG bound inositol lipids with varying degrees of affinity. Among them, profilin displayed preferential binding toward PtdIns(3,4)P2 and PtdIns(3,4,5)P3, whereas gelsolin and CapG bound PtdIns(4,5)P2 with affinity higher than that of D-3 phosphoinositides. Also noteworthy is that gelsolin bound phosphoinositides in a Ca2+-dependent manner. The affinity of gelsolin with PtdIns(4,5)P2 in the presence of Ca2+ was several times higher than that without Ca2+. This is in line with the finding that gelsolin more effectively inhibited phosphoinositide 3-kinase in the presence of Ca2+. Taken together, the differential recognition of phosphoinositides by actin-binding .proteins bears physiological significance in the modulation of important signal-transducing enzymes such as phospholipase C-γl and phosphoinositides 3-kinase by competing for phosphoinositide binding.
|Publication status||Published - 1997 Dec 1|
All Science Journal Classification (ASJC) codes
- Molecular Biology