Binding of p67phox to Nox2 is stabilized by disulfide bonds between cysteines in the 369Cys‐Gly‐Cys371 triad in Nox2 and in p67phox

: A central event in the activation of the phagocyte NADPH oxidase involves binding of p67phox to the dehydrogenase region of Nox2. The identity of the binding site in Nox2 is unknown. By measuring binding of p67phox to synthetic Nox2 peptides, we previously identified a sequence corresponding to Nox2 residues 357-383, as a potential binding site. A key role was attributed to a 369 Cys-Gly-Cys371 triad, shared by peptides 357-371 (peptide 24) and 369-383 (peptide 28). In this study, we show that (1) oxidation of cysteines in peptides 24 and 28 by a variety of oxidants markedly enhances the binding of p67phox ; (2) replacing cysteines by arginine abolishes the response to oxidants and the enhanced binding of p67phox ; (3) oxidants act by generating an intramolecular disulfide bond linking cysteines 369 and 371, generating such bond during peptide synthesis reproduces the effect of oxidants; (4) for the disulfide bond to lead to enhanced binding, cysteines must be separated by an intervening residue; bonds joining adjacent cysteines, or cysteines located on two peptides, do not enhance binding; (5) dissociating disulfide bonds by reducing agents abolishes enhanced binding; (6) treating p67phox with the alkylating agent N-ethylmaleimide suppresses binding; and (7) mutating all nine cysteines in p67phox to serines abolishes binding and diminishes the ability of p67phox to support NADPH oxidase activation in vitro. Results show that the primary interaction of p67phox with Nox2 is followed by a stabilizing step, based on the establishment of disulfide bonds between cysteine(s) in the 369 Cys-Gly-Cys371 triad and cysteine(s) in p67phox .