Molecular interactions of profilin with various phosphoinositides including PtdIns(4,5)P2, PtdIns(3,4,5)P3, and PtdIns(3,4)P2 were examined. Gel filtration and fluorescence titration analyses indicated that the molecular stoichiometry for each profilin and dissociation constants were: PtdIns(3,4)P2: 5.5, 0.3 μM; PtdIns(3,4,5)P3: 6, 1 μM; PtdIns(4,5)P2: 10, 3.6 μM. Moreover, circular dichroism spectroscopy showed that these inositol lipids induced vastly different conformational changes in profilin. The α-helical contents of profilin in the presence of PtdIns(4,5)P2, PtdIns(3,4,5)P3, and PtdIns(3,4)P2 were 17.4%, 11.5%, and 1.4%, respectively, vis-á-vis 9.4% for profilin alone. Based on these spectroscopic data, a working model of phosphoinositide binding to profilin is proposed. This differential recognition bears two folds of physiological implications. First, it provides a putative link between phosphoinositide 3-kinase activation and actin assembly. Secondly, the high affinity of D-3 phosphoinositides with profilin may increase the exposure of PtdIns(4,5)P2 to PLC, thus regulating the production of Ins(1,4,5)P3.
|Publication status||Published - 1996 Dec 1|
All Science Journal Classification (ASJC) codes
- Molecular Biology