Novel human homologues of p47phox and p67phox participate in activation of superoxide-producing NADPH oxidases

The catalytic core of a superoxide-producing NADPH oxidase (Nox) in phagocytes is gp91(phox)/Nox2, a membrane-integrated protein that forms a heterodimer with p22(phox) to constitute flavocytochrome b(558). The cytochrome becomes activated by interacting with the adaptor proteins p47(phox) and p67(phox) as well as the small GTPase Rac. Here we describe the cloning of human cDNAs for novel proteins homologous to p47(phox) and p67(phox), designated p41(nox) and p51(nox), respectively; the former is encoded by NOXO1 (Nox organizer 1), and the latter is encoded by NOXA1 (Nox activator 1). The novel homologue p41(nox) interacts with p22(phox) via the two tandem SH3 domains, as does p47(phox). The protein p51(nox) as well as p67(phox) can form a complex with p47(phox) and with p41(nox) via the C-terminal SH3 domain and binds to GTP-bound Rac via the N-terminal domain containing four tetratricopeptide repeat motifs. These bindings seem to play important roles, since p47(phox) and p67(phox) activate the phagocyte oxidase via the same interactions. Indeed, p41(nox) and p51(nox) are capable of replacing the corresponding classical homologue in activation of gp91(phox). Nox1, a homologue of gp91(phox), also can be activated in cells, when it is coexpressed with p41(nox) and p51(nox), with p41(nox) and p67(phox), or with p47(phox) and p51(nox); in the former two cases, Nox1 is partially activated without any stimulants added, suggesting that p41(nox) is normally in an active state. Thus, the novel homologues p41(nox) and p51(nox) likely function together or in combination with a classical one, thereby activating the two Nox family oxidases.