September 18, 2000Open Access
Activation by Cdc42 and Pip2 of Wiskott-Aldrich Syndrome Protein (Wasp) Stimulates Actin Nucleation by Arp2/3 Complex
Structured PICO
Do PIP2 and Cdc42 activate WASp to stimulate actin nucleation by the Arp2/3 complex?
P
Population
Native WASp (Wiskott-Aldrich Syndrome protein) purified from bovine thymus
I
Intervention
Phosphatidylinositol 4,5 bisphosphate (PIP2) micelles and GTP-Cdc42
C
Comparator
WASp alone (in the presence or absence of GTP-Cdc42 without PIP2)
O
Outcome
Actin nucleation by Arp2/3 complexsurrogate
The study demonstrates that WASp activation for actin nucleation by the Arp2/3 complex requires interaction with both acidic lipids (PIP2) and GTP-Cdc42.
Abstract
We purified native WASp (Wiskott-Aldrich Syndrome protein) from bovine thymus and studied its ability to stimulate actin nucleation by Arp2/3 complex. WASp alone is inactive in the presence or absence of 0.5 microM GTP-Cdc42. Phosphatidylinositol 4,5 bisphosphate (PIP(2)) micelles allowed WASp to activate actin nucleation by Arp2/3 complex, and this was further enhanced twofold by GTP-Cdc42. Filaments nucleated by Arp2/3 complex and WASp in the presence of PIP(2) and Cdc42 concentrated around lipid micelles and vesicles, providing that Cdc42 was GTP-bound and prenylated. Thus, the high concentration of WASp in neutrophils (9 microM) is dependent on interactions with both acidic lipids and GTP-Cdc42 to activate actin nucleation by Arp2/3 complex. The results also suggest that membrane binding increases the local concentrations of Cdc42 and WASp, favoring their interaction.