Ptdlns(3)P regulates the neutrophil oxidase complex by binding to the PX domain of p40(phox)

The production of reactive oxygen species (ROS) by neutrophils has a vital role in defence against a range of infectious agents, and is driven by the assembly of a multi-protein complex containing a minimal core of five prote ins: the two membrane-bound subunits of cytochrome b(558) (gp91(phox) and p 22(phox)) and three soluble factors (GTP-Rac, p47(phox) and p67(phox) (refs 1, 2). This minimal complex can reconstitute ROS formation in vitro in the presence of non-physiological amphiphiles such as sos, p40(phox) has subse quently been discovered as a binding partner for p67(phox) (ref. 3), but it s role in ROS formation is unclear, Phosphoinositide-3-OH kinases (PI(3)Ks) have been implicated in the intracellular signalling pathways coordinating ROS formation(4,5) but through an unknown mechanism. We show that the addi tion of p40(phox) to the minimal core complex allows a lipid product of PI( 3)Ks, phosphatidylinositol 3-phosphate (PtdIns(3)P), to stimulate specifica lly the formation of ROS, This effect was mediated by binding of PtdIns(S)P to the PX domain(6) of p40(phox). These results offer new insights into th e roles for PI(3)Ks and p40(phox) in ROS formation and define a cellular li gand for the orphan PX domain.