The adaptor protein p40phox as a positive regulator of the superoxide-producing phagocyte oxidase

Abstract

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 p40 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 p40 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 .