The adaptor protein p40 super(phox) as a positive regulator of the superoxide-producing phagocyte oxidase

Activation of the superoxide-producing phagocyte NADPH oxidase, crucial in host defense, requires the cytosolic proteins p67 super(phox) and p47 super(phox). They translocate to the membrane upon cell stimulation and activate flavocytochrome b sub(558), the membrane-integrated catalytic core of this enzyme system. The activators p67 super(phox) and p47 super(phox) form a ternary complex together with p40 super(phox), an adaptor protein with unknown function, comprising the PX/PB2, SH3 and PC motif- containing domains: p40 super(phox) associates with p67 super(phox) via binding of the p40 super(phox) PC motif to the p67 super(phox) PB1 domain, while p47 super(phox) directly interacts with p67 super(phox) but not with p40 super(phox). Here we show that p40 super(phox) enhances membrane translocation of p67 super(phox) and p47 super(phox) in stimulated cells, which leads to facilitated production of superoxide. The enhancement cannot be elicited by a mutant p40 super(phox) carrying the D289A substitution in PC or a p67 super(phox) with the K355A substitution in PB1, each being defective in binding to its respective partner. Thus p40 super(phox) participates in activation of the phagocyte oxidase by regulating membrane recruitment of p67 super(phox) and p47 super(phox) via the PB1 PC interaction with p67 super(phox).