Mutations in the PX-SH3A linker of p47phox decouple PI(3,4)P2 binding from NADPH oxidase activation

Association of NOX2 subunits genetic variants with autoimmune diseases

A single nucleotide polymorphism in Ncf1 has been found with a major effect on chronic inflammatory autoimmune diseases in the rat with the surprising observation that a lower reactive oxygen response led to more severe diseases. This finding was subsequently reproduced in the mouse and the effect operates in many different murine diseases through different pathogenic pathways; like models for rheumatoid arthritis, encephalomyelitis, lupus, gout, psoriasis and psoriatic arthritis. The human gene is located in an unstable region with many variable sequence repetitions, which means it has not been included in any genome wide associated screens so far. However, identification of copy number variations and single nucleotide polymorphisms has now clearly shown that major autoimmune diseases are strongly associated with the Ncf1 locus. In systemic lupus erythematosus the associated Ncf1 polymorphism (leading to an amino acid substitution at position 90) is the strongest locus and is associated with a lower reactive oxidative burst response. In addition, more precise mapping analysis of polymorphism of other NOX2 genes reveals that these are also associated with autoimmunity. The identified genetic association shows the importance of redox control and that ROS regulate chronic inflammation instead of promoting it. The genetic identification of Ncf1 polymorphisms now opens for relevant studies of the regulatory mechanisms involved, effects that will have severe consequences in many different pathogenic pathways and understanding of the origin of autoimmune diseases.

Identification of a region in p47phox/NCF1 crucial for phagocytic NADPH oxidase (NOX2) activation

A point mutation in the mouse Ncf1(m1J) gene decreases production of ROS by the phagocytic NOX2 complex. Three mRNA splice variants are expressed, but only one is expressed as a protein, although at lower levels than the WT NCF1 (also known as p47phox). Our aim was to investigate whether the mutant p47phox, lacking 8 aa, is active, but as a result of its low expression, ROS production is decreased in Ncf1(m1J) mice, or whether the mutant p47phox completely lacks the capability to activate the NOX2 complex. The p47phox mutant (Δ228-235), which was equal to the protein in Ncf1(m1J) mice, failed to activate the NOX2 complex. When the deleted region was narrowed down to 2 aa, the p47phox protein remained inactive and failed to translocate to the membrane upon activation. Single amino acid substitutions revealed Thr233 to be vital for ROS production. Residues Tyr231 and Val232 also seemed to be important for p47phox function, as p47phox_Y231G and p47phox_V232G resulted in a >50% decrease in ROS production by the NOX2 complex. In addition, we identified the epitope of the D-10 anti-p47phox mAb. In conclusion, the p47phox protein variant expressed in Ncf1(m1J) mice is completely defective in activating the NOX2 complex to produce ROS, and the effect is dependent on SH3 region amino acids at positions 231-233, which are vital for the proper assembly of the NOX2 complex.

Atypical membrane-embedded phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2)-binding site on p47(phox) Phox homology (PX) domain revealed by NMR

The Phox homology (PX) domain is a functional module that targets membranes through specific interactions with phosphoinositides. The p47(phox) PX domain preferably binds phosphatidylinositol 3,4-bisphosphate (PI(3,4)P(2)) and plays a pivotal role in the assembly of phagocyte NADPH oxidase. We describe the PI(3,4)P(2) binding mode of the p47(phox) PX domain as identified by a transferred cross-saturation experiment. The identified PI(3,4)P(2)-binding site, which includes the residues of helices α1 and α1' and the following loop up to the distorted left-handed PP(II) helix, is located at a unique position, as compared with the phosphoinositide-binding sites of all other PX domains characterized thus far. Mutational analyses corroborated the results of the transferred cross-saturation experiments. Moreover, experiments with intact cells demonstrated the importance of this unique binding site for the function of the NADPH oxidase. The low affinity and selectivity of the atypical phosphoinositide-binding site on the p47(phox) PX domain suggest that different types of phosphoinositides sequentially bind to the p47(phox) PX domain, allowing the regulation of the multiple events that characterize the assembly and activation of phagocyte NADPH oxidase.

The NOXO1β PX domain preferentially targets PtdIns(4,5)P2 and PtdIns(3,4,5)P3

NOXO1β [NOXO1 (Nox organizer 1) β] is a cytosolic protein that, in conjunction with NOXA1 (Nox activator 1), regulates generation of reactive oxygen species by the NADPH oxidase 1 (Nox1) enzyme complex. NOXO1β is targeted to membranes through an N-terminal PX (phox homology) domain. We have used NMR spectroscopy to solve the structure of the NOXO1β PX domain and surface plasmon resonance (SPR) to assess phospholipid specificity. The solution structure of the NOXO1β PX domain shows greatest similarity to that of the phosphatidylinositol 3-kinase-C2α PX domain with regard to the positions and types of residues that are predicted to interact with phosphatidylinositol phosphate (PtdInsP) head groups. SPR experiments identify PtdIns(4,5)P(2) and PtdIns(3,4,5)P(3) as preferred targets of NOXO1β PX. These findings contrast with previous lipid overlay experiments showing strongest binding to monophosphorylated PtdInsP and phosphatidylserine. Our data suggest that localized membrane accumulation of PtdIns(4,5)P(2) or PtdIns(3,4,5)P(2) may serve to recruit NOXO1β and activate Nox1.

Positioning of a polymorphic quantitative trait nucleotide in the Ncf1 gene controlling oxidative burst response and arthritis severity in rats

The Ncf1 gene, encoding the P47(PHOX) protein that regulates production of reactive oxygen species (ROS) by the phagocyte NADPH oxidase (NOX2) complex, is associated with autoimmunity and arthritis severity in rats. We have now identified that the single-nucleotide polymorphism (SNP) resulting in an M153T amino acid substitution mediates arthritis resistance and thus explains the molecular polymorphism underlying the earlier identified Ncf1 gene effect. We identified the SNP in position 153 to regulate ROS production using COS(PHOX) cells transfected with mutated Ncf1. To determine the role of this SNP for control of arthritis, we used the Wistar strain, identified to carry only the postulated arthritis resistant SNP in position 153. When this Ncf1 allele was backcrossed to the arthritis susceptible DA strain, both granulocyte ROS production and arthritis resistance were restored. Position 153 is located in the hinge region between the PX and SH3 domains of P47(PHOX). Mutational analysis of this position revealed a need for an -OH group in the side chain but we found no evidence for phosphorylation. The polymorphism did not affect assembly of the P47(PHOX)/P67(PHOX) complex in the cytosol or membrane localization, but is likely to operate downstream of assembly, affecting activity of the membrane NOX2 complex.

p47phox molecular activation for assembly of the neutrophil NADPH oxidase complex

The p47(phox) cytosolic factor from neutrophilic NADPH oxidase has always been resistant to crystallogenesis trials due to its modular organization leading to relative flexibility. Hydrogen/deuterium exchange coupled to mass spectrometry was used to obtain structural information on the conformational mechanism that underlies p47(phox) activation. We confirmed a relative opening of the protein with exposure of the SH3 Src loops that are known to bind p22(phox) upon activation. A new surface was shown to be unmasked after activation, representing a potential autoinhibitory surface that may block the interaction of the PX domain with the membrane in the resting state. Within this surface, we identified 2 residues involved in the interaction with the PX domain. The double mutant R162A/D166A showed a higher affinity for specific phospholipids but none for the C-terminal part of p22(phox), reflecting an intermediate conformation between the autoinhibited and activated forms.

A prenylated p47phox-p67phox-Rac1 chimera is a Quintessential NADPH oxidase activator: membrane association and functional capacity

The superoxide-generating NADPH oxidase complex of resting phagocytes includes cytochrome b(559), a membrane-associated heterodimer composed of two subunits (Nox2 and p22(phox)), and four cytosolic proteins (p47(phox), p67(phox), Rac, and p40(phox)). Upon stimulation, the cytosolic components translocate to the membrane, as the result of a series of interactions among the cytosolic components and among the cytosolic components and cytochrome b(559) and its phospholipid environment. We described the construction of a tripartite chimera (trimera) consisting of strategic domains of p47(phox), p67(phox), and Rac1, in which interactions among cytosolic components were replaced by fusion (Berdichevsky, Y., Mizrahi, A., Ugolev, Y., Molshanski-Mor, S., and Pick, E. (2007) J. Biol. Chem. 282, 22122-22139). We now fused green fluorescent protein (GFP) to the N terminus of the trimera and found the following. 1) The GFP-p47(phox)-p67(phox)-Rac1 trimera activates the oxidase in amphiphile-dependent and -independent (anionic phospholipid-enriched membrane) cell-free systems. 2) Geranylgeranylation of the GFP-trimera makes it a potent oxidase activator in unmodified (native) membranes and in the absence of amphiphile. 3) Prenylated GFP-trimera binds spontaneously to native membranes (as assessed by gel filtration and in-line fluorometry), forming a tight complex capable of NADPH-dependent, activator-independent superoxide production at rates similar to those measured in canonical cell-free systems. 4) Prenylation of the GFP-trimera supersedes completely the dependence of oxidase activation on the p47(phox) phox homology domain and, partially, on the Rac1 polybasic domain, but the requirement for Trp(193) in p47(phox) persists. Prenylated GFP-p47(phox)-p67(phox)-Rac1 trimera acts as a quintessential single molecule oxidase activator of potential use in high throughput screening of inhibitors.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

Targeting and regulation of reactive oxygen species generation by Nox family NADPH oxidases

Nox family NADPH oxidases serve a variety of functions requiring reactive oxygen species (ROS) generation, including antimicrobial defense, biosynthetic processes, oxygen sensing, and redox-based cellular signaling. We explored targeting, assembly, and activation of several Nox family oxidases, since ROS production appears to be regulated both spatially and temporally. Nox1 and Nox3 are similar to the phagocytic (Nox2-based) oxidase, functioning as multicomponent superoxide-generating enzymes. Factors regulating their activities include cytosolic activator and organizer proteins and GTP-Rac. Their regulation varies, with the following rank order: Nox2 > Nox1 > Nox3. Determinants of subcellular targeting include: (a) formation of Nox-p22(phox) heterodimeric complexes allowing plasma membrane translocation, (b) phospholipids-binding specificities of PX domain-containing organizer proteins (p47(phox) or Nox organizer 1 (Noxo1 and p40(phox)), and (c) variably splicing of Noxo1 PX domains directing them to nuclear or plasma membranes. Dual oxidases (Duox1 and Duox2) are targeted by different mechanisms. Plasma membrane targeting results in H(2)O(2) release, not superoxide, to support extracellular peroxidases. Human Duox1 and Duox2 have no demonstrable peroxidase activity, despite their extensive homology with heme peroxidases. The dual oxidases were reconstituted by Duox activator 2 (Duoxa2) or two Duoxa1 variants, which dictate maturation, subcellular localization, and the type of ROS generated by forming stable complexes with Duox.

Conformational changes in p47(phox) upon activation highlighted by mass spectrometry coupled to hydrogen/deuterium exchange and limited proteolysis

The neutrophil NADPH oxidase is an enzymatic complex involved in innate immunity. Phosphorylation of p47(phox) promotes its translocation with p67(phox) and p40(phox), followed by membrane interaction and assembly with flavocytochrome b(558) into a functional complex. To characterise p47(phox) conformational changes during activation, we used wild-type and the S303/304/328E triple mutant mimicking the phosphorylated state. Hydrogen/deuterium exchange and limited proteolysis coupled to mass spectrometry were used to discriminate between the various structural models. An increase in deuteration confirmed that p47(phox) adopts an open and more flexible conformation after activation. Limited proteolysis correlated this change with increased auto-inhibitory region (AIR) accessibility. These results establish a structural link between the AIR release and the exposure of the Phox homology (PX) domain.