Solution structure of the tandem Src homology 3 domains of p47 ^phox in an autoinhibited form

The phagocyte NADPH oxidase is a multisubunit enzyme responsible for the generation of superoxide anions (O₂^.-) that kill invading microorganisms. p47^phox is a cytosolic subunit of the phagocyte NADPH oxidase, which plays a crucial role in the assembly of the activated NADPH oxidase complex. The molecular shapes of the p47^phox tandem SH3 domains either with or without a polybasic/autoinhibitory region (PBR/AIR) at the C terminus were studied using small angle x-ray scattering. The tandem SH3 domains with PBR/AIR formed a compact globular structure, whereas the tandem SH3 domains lacking the PBR/AIR formed an elongated structure. Alignment anisotropy analysis by NMR based on the residual dipolar couplings revealed that the tandem SH3 domains with PBR/AIR were in good agreement with a globular module corresponding to the split half of the intertwisted dimer in crystalline state. The structure of the globular module was elucidated to represent a 1solution structure of the tandem SH3 domain in the autoinhibited form, where the PBR/AIR bundled the tandem SH3 domains and the linker forming a closed structure. Once PBR/AIR is released by phosphorylation, rearrangements of the SH3 domains may occur, forming an open structure that binds to the cytoplasmic proline-rich region of membrane-bound p22^phox.