p40^phox as an alternative organizer to p47^phox in Nox2 activation: A new mechanism involving an interaction with p22^phox

p40^phox activated phagocyte NADPH oxidase without p47^phox in a cell-free system consisting of p67^phox, Rac and cytochrome b₅₅₈ relipidated with phosphatidylinositol 3-phosphate. The activation reached to 70% of that by p47^phox. Addition of p47^phox slightly increased the activation, but not additively. p40^phox improved the efficiency of p67^phox in the activation. The C-terminus-truncated p67^phox, p40^phox(D289A), p40^phox(R58A), or p40^phox(W207R) showed an impaired activation. A peptide corresponding to the p22^phox Pro-rich region suppressed the activation, and far-western blotting revealed its interaction with p40^phox SH3 domain. Thus, p40^phox can substitute for p47^phox in the activation, interacting with p22^phox and p67^phox through their specific regions.