The adaptor protein p40 ^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 ^phox and p47 ^phox . They translocate to the membrane upon cell stimulation and activate flavocytochrome b ₅₅₈ , the membrane-integrated catalytic core of this enzyme system. The activators p67 ^phox and p47 ^phox form a ternary complex together with p4O ^phox , an adaptor protein with unknown function, comprising the PX/PB2, SH3 and PC motif-containing domains: p40 ^phox associates with p67 ^phox via binding of the p40 ^phox PC motif to the p67 ^phox PB1 domain, while p47 ^phox directly interacts with p67 ^phox but not with p41 ^phox . Here we show that p40 ^phox enhances membrane translocation of p67 ^phox and p47 ^phox in stimulated cells, which leads to facilitated production of superoxide. The enhancement cannot be elicited by a mutant p40 ^phox carrying the D289A substitution in PC or a p67 ^phox with the K355A substitution in PB1, each being defective in binding to its respective partner. Thus p40 ^phox participates in activation of the phagocyte oxidase by regulating membrane recruitment of p67 ^phox and p47 ^phox via the PB1-PC interaction with p67 ^phox .