Protein Delivery by Pseudomonas Type III Secretion System: Ex Vivo Complementation of p67phox-Deficient Chronic Granulomatous Disease

Bacterial type III secretion system drives the translocation of virulence factors into the cystosol of host target cells. In phagocytes and in Epstein–Barr virus immortalized B lymphocytes, NADPH oxidase generates O−2 through an electron transfer chain the activity of which depends on the assembly of three, p67phox, p47phox and p40phox cytosolic activating factors with Rac 1/2 and a membrane redox component, cytochrome b558. In p67phox deficient chronic granulomatous disease (CGD) patients, p67-phox is missing and NADPH oxidase activity is abolished. ExoS is a virulence factor of Pseudomonas aeruginosa which is secreted via the type III secretion system: it was fused with p67phox. Pseudomonas aeruginosa synthesized and translocated the hybrid ExoS-p67phox fusion protein into the cytosol of B lymphocytes via the type III secretion system. Purified ExoS-p67phox hybrid protein was as efficient as normal recombinant p67phox in cell-free reconstitution of NADPH oxidase activity. Therefore, ExoS-p67phox was transferred via the type III secretion system of Pseudomonas aeruginosa into the cytosol of B lymphocytes from a p67phox-deficient CGD patient and functionally reconstituted NADPH oxidase activity. In the complementation process, ExoS acted as a molecular courier for protein delivery: the reconstitution of an active NADPH oxidase complex suggests type III secretion system to be a new approach for cellular therapy.