Assembly of the phagocyte NADPH oxidase: binding of Src homology 3 domains to proline-rich targets

Abstract

The NADPH oxidase responsible for generation of superoxide anion and related microbicidal oxidants by phagocytes is assembled from at least five distinct proteins. Two are cytosolic components (p47-phox and p67-phox) that contain Src homology 3 (SH3) domains and associate with a transmembrane cytochrome b558 upon activation. We show here that the SH3 domains of p47-phox bind to proline-rich sequences in p47-phox itself and the p22-phox subunit of cytochrome b558. Binding of the p47-phox SH3 domains to p22-phox was abolished by a mutation in one proline-rich sequence (Pro156-->Gln) noted in a distinct form of chronic granulomatous disease and was inhibited by a short proline-rich synthetic peptide corresponding to residues 149-162 of p22-phox. Expression of mutated p22-phox did not restore oxidase activity to p22-phox-deficient B cells and did not enable p22-phox-dependent translocation of p47-phox to membranes in phorbol ester-stimulated cells. We also show that the cytosolic oxidase components associate with one another through the C-terminal SH3 domain of p67-phox and a proline-rich C-terminal sequence in p47-phox. These SH3 target sites conform to consensus features deduced from SH3 binding sites in other systems. We propose a model in which the oxidase complex assembles through a mechanism involving SH3 domains of both cytosolic proteins and cognate proline-rich targets in other oxidase components.