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Examines the role of human homologue p47 and p67 adapter proteins in the activation of superoxide-producing NAD(P)H oxidases. Structure and domain architecture of p41, a novel homologue of p47; Interaction of human p41 with other oxidase factors; Effects of p41 and p51 on activation of the phagocyte NAD(P)H oxidase.

The causative agent of Legionnaires disease, Legionellapneumophila, forms a replicative vacuole in phagocytes by means of the intracellular multiplication/defective organelle trafficking (1cm/Dot) type IV secretion system and translocated effector proteins, some of which subvert host GTP and phosphoinositide (P1) metabolism. The 1cm/Dot substrate SidC anchors to the membrane of Legionella-containing vacuoles (LCVs) by specifically binding to phosphatidylinositol 4-phosphate (Ptdlns(4)P). Using a nonbiased screen for novel L. pneumophila P1-binding proteins, we identified the Rabi guanine nucleotide exchange factor (GEF) SidM/DrrA as the predominant Ptdlns(4)P-binding protein. Purified SidM specifically and directly bound to Ptdlns(4)P, whereas the SidM-interacting 1cm/Dot substrate LidA preferentially bound Ptdlns(3)P but also Ptdlns(4)P, and the L. pneumophila Arfi GEF Ra1F did not bind to any PIs. The Ptdlns(4)P-binding domain of SidM was mapped to the 12-kDa C-terminal sequence, termed "P4M" (tdIns P binding of SidM/DrrA). The isolated P4M domain is largely helical and displayed higher Ptdlns(4)P binding activity in the context of the a-helical, monomeric full-length protein. SidM constructs containing P4M were translocated by 1cm/Dot-proficient L. pneumophila and localized to the LCV membrane, indicating that SidM anchors to Ptdlns(4)P on LCVs via its P4M domain. An L. pneumophila ΔsidM mutant strain displayed significantly higher amounts of SidC on LCVs, suggesting that SidM and SidC compete for limiting amounts of Ptdlns(4)P on the vacuole. Finally, RNA interference revealed that Ptdlns(4)P on LCVs is specifically formed by host Ptdlns 4-kinase IIIβ. Thus, L. pneumophila exploits Ptdlns(4)P produced by Ptdlns 4-kinase IIIβ to anchor the effectors SidC and SidM to LCVs. [ABSTRACT FROM AUTHOR]