Tetratricopeptide repeat (TPR) motifs of p67(phox) participate in interaction with the small GTPase Rac and activation of the phagocyte NADPH oxidase

The small GTPase Rac functions as a molecular switch in several important c ellular events including cytoskeletal reorganization and activation of the phagocyte NADPH oxidase, the latter of which leads to production of superox ide, a precursor of microbicidal oxidants. During formation of the active o xidase complex at the membrane, the GTP-bound Rac appears to interact with the N-terminal region of p67(phox), another indispensable activator that tr anslocates from the cytosol upon phagocyte stimulation. Here we show that t he p67(phox) N terminus lacks the CRIB motif, a well known Rac target, but contains four tetratricopeptide repeat (TPR) motifs with highly alpha-helic al structure. Disruption of any of the N-terminal three TPRs, but the last one, results in defective interaction with Rac, while all the four are requ ired for the NADPH oxidase activation. We also find that Arg-102 in the thi rd repeat is likely involved in binding to Rac via an ionic interaction, an d that replacement of this residue with Glu completely abrogates the capabi lity of activating the oxidase both in vivo and in vitro, Thus the TPR moti fs of p67(phox) are packed to function as a Rac target, thereby playing a c rucial role in the active oxidase complex formation.