NADPH oxidase activator p67phox behaves in solution as a multidomain protein with semi-flexible linkers

The NADPH oxidase complex is involved in the destruction of phagocytosed pathogens through the production of reactive oxygen species. This activatable complex consists of a membranous heterodimeric flavocytochrome b, a small G-protein Rac1/Rac2 and cytosolic factors, p47phox, p67phox and p40phox. p67phox, due to its modular structure, is the NADPH oxidase component for which global structure information is most scarce despite its mandatory role in activation and its central position in the whole complex organization. Indeed, p67phox is the only factor establishing interaction with all others. In this study, we report the SAXS analysis of p67phox. Our data reveals that p67phox behaves as a multidomain protein with semi-flexible linkers. On the one hand, it appears to be a very elongated molecule with its various domains organized as beads on a string. Linkers are predicted to be partially or mainly unstructured and features of our experimental data do point towards inter-domain flexibility. On the other hand, our work also suggests that the protein is not as extended as unstructured linkers could allow, thereby implying the existence of intra-molecular interactions within p67phox. We suggest that the dual character of p67phox conformation in solution is central to ensure the numerous interactions to be accommodated.