In the phagocytic cell, NADPH oxidase (Nox2) system, cytoplasmic regulators (p47phox, p67phox, p40phox, and Rac) translocate and associate with the membrane-spanning flavocytochrome b 558, leading to activation of superoxide production. We examined membrane targeting of phox proteins and explored conformational changes in p40phox that regulate its translocation to membranes upon stimulation. GFP-p40phox translocates to early endosomes, whereas GFP-p47phox translocates to the plasma membrane in response to arachidonic acid. In contrast, GFP-p67phox does not translocate to membranes when expressed alone, but it is dependent on p40phox and p47phox for its translocation to early endosomes or the plasma membrane, respectively. Translocation of GFP-p40phox or GFP-p47 phox to their respective membrane-targeting sites is abolished by mutations in their phox (PX) domains that disrupt their interactions with their cognate phospholipid ligands. Furthermore, GFP-p67phox translocation to either membrane is abolished by mutations that disrupt its interaction with p40phox or p47phox. Finally, we detected a head-to-tail (PX-Phox and Bem1 [PB1] domain) intramolecular interaction within p40 phox in its resting state by deletion mutagenesis, cell localization, and binding experiments, suggesting that its PX domain is inaccessible to interact with phosphatidylinositol 3-phosphate without cell stimulation. Thus, both p40phox and p47phox function as diverse p67 phox "carrier proteins" regulated by the unmasking of membrane-targeting domains in distinct mechanisms.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology