45K actin filament-severing protein from sea urchin eggs: interaction with phosphatidylinositol-4,5-bisphosphate.

An actin filament-severing activity of 45K protein isolated from sea urchin eggs was abolished when this protein was incubated with phosphatidylinositol-4,5-bisphosphate (PIP2). This effect was specific to PIP2 since phosphatidylinositol, phosphatidylinositol-4-monophosphate, inositol-1,4,5-trisphosphate, and phosphatidylserine did not show such an effect at the same concentration. Digestion of PIP2 with phospholipase C eliminated the effect. On the other hand, PIP2 did not affect either the formation of 45K protein-actin complex or actin filament-capping activity of the complex. Possible implication of the binding of PIP2 to 45K protein in cytoskeleton formation after fertilization of sea urchin eggs is discussed.