Structural Biology of Phagocyte oxidation

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The phagocyte NADPH oxidase, a defense system for microbial infection comprises membrane bound flavocytochrome cyt b_<558> (gp91^<phox> and p22^<phox>) and cytosolic factors including p67^<phox>, p47^<phox>, p40^<phox> and small GTPase Rac. Upon microbial invasion, the cytosolic factors are translocated to the membrane to bind to cyt b_<558>, which activates a redox-core of cyt b_<558> and generates O_2-, a precursor of microbicidal oxidants. The activation of the NADPH oxidase is tightly regulated through conformation change of the tandem SH3 domain of p47^<phox>.Recently, the crystal structure of the tandem SH3 domains in the autoinhibited form (Groemping et al., Cell,2003, Yuzawa et al., Genes Cells,2004, J Biol Chem.,2004) and the activated form (Groemping et al., Cell,2003) were determined. Interestingly, the tandem SH3 domains formed an intertwisted dimer in the crystal state but the splitted half was considered to be physiologically relevent. Here, we report the three dimensional structures of the masked and unmasked states of the tandem SH3 domains by NMR. Furthermore, we elucidated the global conformation change of the tandem SH3 domains from the masked to unmasked states by small angle X-ray scattering. Based on the present structural data, we discussed the activation mechanism of the phagocyte NADPH oxidase.