NMR solution structure of the tandem Src homology 3 domains of p47phox complexed with a p22phox-derived proline-rich peptide

Structural profiles of the full phagocyte NADPH oxidase unveiled by combining computational biology and experimental knowledge

The phagocyte NADPH oxidase (NOX2) is an enzyme, crucial for innate immune defense, producing reactive oxygen species necessary for pathogen destruction. Its activation requires the assembly of soluble proteins (p47phox, p40phox, p67phox, and Rac) with the membrane-bound flavocytochrome b558 (cytb558). We combined circular-dichroism analyses, with decades of experimental data, to filter structural models of the NADPH oxidase complex generated by the artificial intelligence program AlphaFold2 (AF2). The predicted patterns tend to closely resemble the active states of the proteins, as shown by the compact structure of the cytb558, whose dehydrogenase domain is stabilized closer to the membrane. The modeling of the interaction of p47phox with cytb558, which is the initial assembly and activation steps of the NADPH oxidase, enables us to describe how the C-terminus of p47phox interacts with the cytb558. Combining the AF2 cytb558 -p47phox model and its classical molecular dynamics simulations, we highlighted new hydrophobic lipid insertions of p47phox, particularly at residues Trp80-Phe81 of its PX domain. The AF2 models also revealed the implications of intrinsically disordered regions, such as the fragment between the PX domain and the SH3 regions of p47phox, in ensuring distant protein-protein and membrane-protein interactions. Finally, the AF2 prediction of the cytb558-Trimera model highlighted the importance of leaving Rac1 as a separate protein to reach an active state of the NADPH oxidase complex. Altogether, our step-by-step approach provides a structural model of the active complex showing how disordered regions and specific lipid and protein interactions can enable and stabilize the multi-subunit assembly.

My 50-Plus Years of Academic Research Collaborations with Industry. A Retrospective

A retrospective is presented highlighting the synthesis of selected "first-in-kind" natural products, their synthetic analogues, structure elucidations, and rationally designed bioactive synthetic compounds that were accomplished because of collaborations with past and present pharmaceutical and agrochemical companies. Medicinal chemistry projects involving structure-based design exploiting cocrystal structures of small molecules with biologically relevant enzymes, receptors, and bacterial ribosomes with synthetic small molecules leading to marketed products, clinical candidates, and novel drug prototypes were realized in collaboration. Personal reflections, historical insights, behind the scenes stories from various long-term projects are shared in this retrospective article.

The NADPH oxidase 2 subunit p47phox binds to the WAVE regulatory complex and p22phox in a mutually exclusive manner

The actin cytoskeleton and reactive oxygen species (ROS) both play crucial roles in various cellular processes. Previous research indicated a direct interaction between two key components of these systems: the WAVE1 subunit of the WAVE regulatory complex (WRC), which promotes actin polymerization and the p47phox subunit of the NADPH oxidase 2 complex (NOX2), which produces ROS. Here, using carefully characterized recombinant proteins, we find that activated p47phox uses its dual Src homology 3 domains to bind to multiple regions within the WAVE1 and Abi2 subunits of the WRC, without altering WRC's activity in promoting Arp2/3-mediated actin polymerization. Notably, contrary to previous findings, p47phox uses the same binding pocket to interact with both the WRC and the p22phox subunit of NOX2, albeit in a mutually exclusive manner. This observation suggests that when activated, p47phox may separately participate in two distinct processes: assembling into NOX2 to promote ROS production and engaging with WRC to regulate the actin cytoskeleton.

Structure of human phagocyte NADPH oxidase in the activated state

Phagocyte NADPH oxidase, a protein complex with a core made up of NOX2 and p22 subunits, is responsible for transferring electrons from intracellular NADPH to extracellular oxygen1. This process generates superoxide anions that are vital for killing pathogens1. The activation of phagocyte NADPH oxidase requires membrane translocation and the binding of several cytosolic factors2. However, the exact mechanism by which cytosolic factors bind to and activate NOX2 is not well understood. Here we present the structure of the human NOX2-p22 complex activated by fragments of three cytosolic factors: p47, p67 and Rac1. The structure reveals that the p67-Rac1 complex clamps onto the dehydrogenase domain of NOX2 and induces its contraction, which stabilizes the binding of NADPH and results in a reduction of the distance between the NADPH-binding domain and the flavin adenine dinucleotide (FAD)-binding domain. Furthermore, the dehydrogenase domain docks onto the bottom of the transmembrane domain of NOX2, which reduces the distance between FAD and the inner haem. These structural rearrangements might facilitate the efficient transfer of electrons between the redox centres in NOX2 and lead to the activation of phagocyte NADPH oxidase.

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Virtual Screening of Peptide Libraries: The Search for Peptide-Based Therapeutics Using Computational Tools

Over the last few decades, we have witnessed growing interest from both academic and industrial laboratories in peptides as possible therapeutics. Bioactive peptides have a high potential to treat various diseases with specificity and biological safety. Compared to small molecules, peptides represent better candidates as inhibitors (or general modulators) of key protein-protein interactions. In fact, undruggable proteins containing large and smooth surfaces can be more easily targeted with the conformational plasticity of peptides. The discovery of bioactive peptides, working against disease-relevant protein targets, generally requires the high-throughput screening of large libraries, and in silico approaches are highly exploited for their low-cost incidence and efficiency. The present review reports on the potential challenges linked to the employment of peptides as therapeutics and describes computational approaches, mainly structure-based virtual screening (SBVS), to support the identification of novel peptides for therapeutic implementations. Cutting-edge SBVS strategies are reviewed along with examples of applications focused on diverse classes of bioactive peptides (i.e., anticancer, antimicrobial/antiviral peptides, peptides blocking amyloid fiber formation).

Targeting NOX2 with Bivalent Small-Molecule p47phox-p22phox Inhibitors

Nicotinamide adenine dinucleotide phosphate oxidase isoform 2 (NOX2) is an enzymatic complex whose function is the regulated generation of reactive oxygen species (ROS). NOX2 activity is central to redox signaling events and antibacterial response, but excessive ROS production by NOX2 leads to oxidative stress and inflammation in a range of diseases. The protein-protein interaction between the NOX2 subunits p47phox and p22phox is essential for NOX2 activation, thus p47phox is a potential drug target. Previously, we identified 2-aminoquinoline as a fragment hit toward p47phoxSH3A-B and converted it to a bivalent small-molecule p47phox-p22phox inhibitor (Ki = 20 μM). Here, we systematically optimized the bivalent compounds by exploring linker types and positioning as well as substituents on the 2-aminoquinoline part and characterized the bivalent binding mode with biophysical methods. We identified several compounds with submicromolar binding affinities and cellular activity and thereby demonstrated that p47phox can be targeted by potent small molecules.

New NADPH Oxidase 2 Inhibitors Display Potent Activity against Oxidative Stress by Targeting p22phox-p47phox Interactions

NADPH oxidase (NOX2) is responsible for reactive oxygen species (ROS) production in neutrophils and has been recognized as a key mediator in inflammatory and cardiovascular pathologies. Nevertheless, there is a lack of specific NOX2 pharmacological inhibitors. In medicinal chemistry, heterocyclic compounds are essential scaffolds for drug design, and among them, indole is a very versatile pharmacophore. We tested the hypothesis that indole heteroaryl-acrylonitrile derivatives may serve as NOX2 inhibitors by evaluating the capacity of 19 of these molecules to inhibit NOX2-derived ROS production in human neutrophils (HL-60 cells). Of these compounds, C6 and C14 exhibited concentration-dependent inhibition of NOX2 (IC₅₀~1 µM). These molecules also reduced NOX2-derived oxidative stress in cardiomyocytes and prevented cardiac damage induced by ischemia-reperfusion. Compound C6 significantly reduced the membrane translocation of p47^phox, a cytosolic subunit that is required for NOX2 activation. Molecular docking analyses of the binding modes of these molecules with p47^phox indicated that C6 and C14 interact with specific residues in the inner part of the groove of p47^phox, the binding cavity for p22^phox. This combination of methods showed that novel indole heteroaryl acrylonitriles represent interesting lead compounds for developing specific and potent NOX2 inhibitors.

Identification of a Noxo1 inhibitor by addition of a polyethylene glycol chain

Reactive oxygen species (ROS) are a heterogeneous group of highly reactive ions and molecules derived from molecular oxygen (O₂) which can cause DNA damage and lead to skin cancer. NADPH oxidase 1 (Nox1) is a major producer of ROS in the skin upon exposure to ultraviolet light. Functionally, Nox1 forms a holoenzyme complex that generates two superoxide molecules and reduces NADPH. The signaling activation occurs when the organizer subunit Noxo1 translocates to the plasma membrane bringing a cytochrome p450, through interaction with Cyba. We propose to design inhibitors that prevent Cyba-Noxo1 binding as a topical application to reduce UV-generated ROS in human skin cells. Design started from an apocynin backbone structure to generate a small molecule to serve as an anchor point. The initial compound was then modified by addition of a polyethylene glycol linked biotin. Both inhibitors were found to be non-toxic in human keratinocyte cells. Further in vitro experiments using isothermal calorimetric binding quantification showed the modified biotinylated compound bound Noxo1 peptide with a K_D of 2 nM. Both using isothermal calorimetric binding and MALDI (TOF) MS showed that binding of a Cyba peptide to Noxo1 was blocked. In vivo experiments were performed using donated skin explants with topical application of the two inhibitors. Experiments show that ultraviolet light exposure of with the lead compound was able to reduce the amount of cyclobutene pyrimidine dimers in DNA, a molecule known to lead to carcinogenesis. Further synthesis showed that the polyethylene glycol but not the biotin was essential for inhibition.

Exploring the Potential of Black Soldier Fly Larval Proteins as Bioactive Peptide Sources through in Silico Gastrointestinal Proteolysis: A Cheminformatic Investigation

Despite their potential as a protein source for human consumption, the health benefits of black soldier fly larvae (BSFL) proteins following human gastrointestinal (GI) digestion are poorly understood. This computational study explored the potential of BSFL proteins to release health-promoting peptides after human GI digestion. Twenty-six proteins were virtually proteolyzed with GI proteases. The resultant peptides were screened for high GI absorption and non-toxicity. Shortlisted peptides were searched against the BIOPEP-UWM and Scopus databases to identify their bioactivities. The potential of the peptides as inhibitors of myeloperoxidase (MPO), NADPH oxidase (NOX), and xanthine oxidase (XO), as well as a disruptor of Keap1–Nrf2 protein–protein interaction, were predicted using molecular docking and dynamics simulation. Our results revealed that about 95% of the 5218 fragments generated from the proteolysis of BSFL proteins came from muscle proteins. Dipeptides comprised the largest group (about 25%) of fragments arising from each muscular protein. Screening of 1994 di- and tripeptides using SwissADME and STopTox tools revealed 65 unique sequences with high GI absorption and non-toxicity. A search of the databases identified 16 antioxidant peptides, 14 anti-angiotensin-converting enzyme peptides, and 17 anti-dipeptidyl peptidase IV peptides among these sequences. Results from molecular docking and dynamic simulation suggest that the dipeptide DF has the potential to inhibit Keap1–Nrf2 interaction and interact with MPO within a short time frame, whereas the dipeptide TF shows promise as an XO inhibitor. BSFL peptides were likely weak NOX inhibitors. Our in silico results suggest that upon GI digestion, BSFL proteins may yield high-GI-absorbed and non-toxic peptides with potential health benefits. This study is the first to investigate the bioactivity of peptides liberated from BSFL proteins following human GI digestion. Our findings provide a basis for further investigations into the potential use of BSFL proteins as a functional food ingredient with significant health benefits.

Computational Screening for the Anticancer Potential of Seed-Derived Antioxidant Peptides: A Cheminformatic Approach

Some seed-derived antioxidant peptides are known to regulate cellular modulators of ROS production, including those proposed to be promising targets of anticancer therapy. Nevertheless, research in this direction is relatively slow owing to the inevitable time-consuming nature of wet-lab experimentations. To help expedite such explorations, we performed structure-based virtual screening on seed-derived antioxidant peptides in the literature for anticancer potential. The ability of the peptides to interact with myeloperoxidase, xanthine oxidase, Keap1, and p47^phox was examined. We generated a virtual library of 677 peptides based on a database and literature search. Screening for anticancer potential, non-toxicity, non-allergenicity, non-hemolyticity narrowed down the collection to five candidates. Molecular docking found LYSPH as the most promising in targeting myeloperoxidase, xanthine oxidase, and Keap1, whereas PSYLNTPLL was the best candidate to bind stably to key residues in p47^phox. Stability of the four peptide-target complexes was supported by molecular dynamics simulation. LYSPH and PSYLNTPLL were predicted to have cell- and blood-brain barrier penetrating potential, although intolerant to gastrointestinal digestion. Computational alanine scanning found tyrosine residues in both peptides as crucial to stable binding to the targets. Overall, LYSPH and PSYLNTPLL are two potential anticancer peptides that deserve deeper exploration in future.

Effect of Disease Causing Missense Mutations on Intrinsically Disordered Regions in Proteins

BACKGROUND

It is well known that disease-causing missense mutations (DCMMs) reduce the structural stability/integrity of the proteins with well-defined 3D structures, thereby impacting their molecular functions. However, it is not known in what way DCMMs affect the intrinsically disordered proteins (IDPs) that do not adopt well defined stable 3D structures.

METHODS

In order to investigate how DCMMs may impact intrinsically disordered regions (IDRs) in proteins, we undertook Molecular Dynamics (MD) based studies on three different examples of functionally important IDRs with known DCMMs. Our studies revealed that the functional impact of DCMMs is in reducing the conformational heterogeneity of IDRs, which is intrinsic and quintessential for their multi-faceted cellular roles.

RESULTS

These results are reinforced by energy landscapes of the wildtype and mutant IDRs where the former is characterized by many local minima separated by low barriers, whereas the latter are characterized by one global minimum and several local minima separated by high energy barriers. Our MD based studies also indicate that DCMMs stabilize very few structural possibilities of IDRs either by the newly formed interactions induced by the substituted side chains or by means of restricted or increased flexibilities of the backbone conformations at the mutation sites.

CONCLUSION

Furthermore, the structural possibilities stabilized by DCMMs do not support the native functional roles of the IDRs, thereby leading to disease conditions.

Characterization of the Intramolecular Interactions and Regulatory Mechanisms of the Scaffold Protein Tks4

The scaffold protein Tks4 is a member of the p47^phox-related organizer superfamily. It plays a key role in cell motility by being essential for the formation of podosomes and invadopodia. In addition, Tks4 is involved in the epidermal growth factor (EGF) signaling pathway, in which EGF induces the translocation of Tks4 from the cytoplasm to the plasma membrane. The evolutionarily-related protein p47^phox and Tks4 share many similarities in their N-terminal region: a phosphoinositide-binding PX domain is followed by two SH3 domains (so called “tandem SH3”) and a proline-rich region (PRR). In p47^phox, the PRR is followed by a relatively short, disordered C-terminal tail region containing multiple phosphorylation sites. These play a key role in the regulation of the protein. In Tks4, the PRR is followed by a third and a fourth SH3 domain connected by a long (~420 residues) unstructured region. In p47^phox, the tandem SH3 domain binds the PRR while the first SH3 domain interacts with the PX domain, thereby preventing its binding to the membrane. Based on the conserved structural features of p47^phox and Tks4 and the fact that an intramolecular interaction between the third SH3 and the PX domains of Tks4 has already been reported, we hypothesized that Tks4 is similarly regulated by autoinhibition. In this study, we showed, via fluorescence-based titrations, MST, ITC, and SAXS measurements, that the tandem SH3 domain of Tks4 binds the PRR and that the PX domain interacts with the third SH3 domain. We also investigated a phosphomimicking Thr-to-Glu point mutation in the PRR as a possible regulator of intramolecular interactions. Phosphatidylinositol-3-phosphate (PtdIns(3)P) was identified as the main binding partner of the PX domain via lipid-binding assays. In truncated Tks4 fragments, the presence of the tandem SH3, together with the PRR, reduced PtdIns(3)P binding, while the presence of the third SH3 domain led to complete inhibition.

NADPH Oxidases (NOX): An Overview from Discovery, Molecular Mechanisms to Physiology and Pathology

The reactive oxygen species (ROS)-producing enzyme NADPH oxidase (NOX) was first identified in the membrane of phagocytic cells. For many years, its only known role was in immune defense, where its ROS production leads to the destruction of pathogens by the immune cells. NOX from phagocytes catalyzes, via one-electron trans-membrane transfer to molecular oxygen, the production of the superoxide anion. Over the years, six human homologs of the catalytic subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the NOX2/gp91phox component present in the phagocyte NADPH oxidase assembly itself, the homologs are now referred to as the NOX family of NADPH oxidases. NOX are complex multidomain proteins with varying requirements for assembly with combinations of other proteins for activity. The recent structural insights acquired on both prokaryotic and eukaryotic NOX open new perspectives for the understanding of the molecular mechanisms inherent to NOX regulation and ROS production (superoxide or hydrogen peroxide). This new structural information will certainly inform new investigations of human disease. As specialized ROS producers, NOX enzymes participate in numerous crucial physiological processes, including host defense, the post-translational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. These diversities of physiological context will be discussed in this review. We also discuss NOX misregulation, which can contribute to a wide range of severe pathologies, such as atherosclerosis, hypertension, diabetic nephropathy, lung fibrosis, cancer, or neurodegenerative diseases, giving this family of membrane proteins a strong therapeutic interest.

The NADPH Oxidase Family and Its Inhibitors

Significance: The oxidative stress, resulting from an imbalance in the production and scavenging of reactive oxygen species (ROS), is known to be involved in the development and progression of several pathologies. The excess of ROS production is often due to an overactivation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) and for this reason these enzymes became promising therapeutic targets. However, even if NOX are now well characterized, the development of new therapies is limited by the lack of highly isoform-specific inhibitors. Recent Advances: In the past decade, several groups and laboratories have screened thousands of molecules to identify new specific inhibitors with low off-target effects. These works have led to the characterization of several new potent NOX inhibitors; however, their specificity varies a lot depending on the molecules. Critical Issues: Here, we are reviewing more than 25 known NOX inhibitors, focusing mainly on the newly identified ones such as APX-115, NOS31, Phox-I1 and 2, GLX7013114, and GSK2795039. To have a better overall view of these molecules, the inhibitors were classified according to their specificity, from pan-NOX inhibitors to highly isoform-specific ones. We are also presenting the use of these compounds both in vitro and in vivo. Future Directions: Several of these new molecules are potent and very specific inhibitors that could be good candidates for the development of new drugs. Even if the results are very promising, most of these compounds were only validated in vitro or in mice models and further investigations will be required before using them as potential therapies.

Class I phosphoinositide 3-kinases control sustained NADPH oxidase activation in adherent neutrophils

Phagocytes, especially neutrophils, can produce reactive oxygen species (ROS), through the activation of the NADPH oxidase (NOX2). Although this enzyme is crucial for host-pathogen defense, ROS production by neutrophils can be harmful in several pathologies such as cardiovascular diseases or chronic pulmonary diseases. The ROS production by NOX2 involves the assembly of the cytosolic subunits (p67^phox, p47^phox, and p40^phox) and Rac with the membrane subunits (gp91^phox and p22^phox). Many studies are devoted to the activation of NOX2. However, the mechanisms that cause NADPH oxidase deactivation and thus terminate ROS production are not well known. Here we investigated the ability of class I phosphoinositide 3-kinases (PI3Ks) to sustain NADPH oxidase activation. The NADPH oxidase activation was triggered by seeding neutrophil-like PLB-985 cells, or human neutrophils on immobilized fibrinogen. Adhesion of the neutrophils, mediated by β2 integrins, induced activation of the NADPH oxidase and translocation of the cytosolic subunits at the plasma membrane. Inhibition of class I PI3Ks, and especially PI3Kβ, terminated ROS production. This deactivation of NOX2 is due to the release of the cytosolic subunits, p67^phox and p47^phox from the plasma membrane. Overexpression of an active form of Rac 1 did not prevent the drop of ROS production upon inhibition of class I PI3Ks. Moreover, the phosphorylation of p47^phox at S328, a potential target of kinases activated by the PI3K pathway, was unchanged. Our results indicate that the experimental downregulation of class I PI3K products triggers the plasma membrane NADPH oxidase deactivation. Release of p47^phox from the plasma membrane may involve its PX domains that bind PI3K products.

Developing Inhibitors of the p47phox-p22phox Protein-Protein Interaction by Fragment-Based Drug Discovery

Nicotinamide adenine dinucleotide phosphate oxidase isoform 2 is an enzyme complex, which generates reactive oxygen species and contributes to oxidative stress. The p47phox-p22phox interaction is critical for the activation of the catalytical NOX2 domain, and p47phox is a potential target for therapeutic intervention. By screening 2500 fragments using fluorescence polarization and a thermal shift assay and validation by surface plasmon resonance, we found eight hits toward the tandem SH3 domain of p47phox (p47phox^SH3A-B) with K_D values of 400-600 μM. Structural studies revealed that fragments 1 and 2 bound two separate binding sites in the elongated conformation of p47phox^SH3A-B and these competed with p22phox for binding to p47phox^SH3A-B. Chemical optimization led to a dimeric compound with the ability to potently inhibit the p47phox^SH3A-B-p22phox interaction (K_i of 20 μM). Thereby, we reveal a new way of targeting p47phox and present the first report of drug-like molecules with the ability to bind p47phox and inhibit its interaction with p22phox.

Soluble Regulatory Proteins for Activation of NOX Family NADPH Oxidases

NOX family NADPH oxidases deliberately produce reactive oxygen species and thus contribute to a variety of biological functions. Of seven members in the human family, the three oxidases NOX2, NOX1, and NOX3 form a heterodimer with p22^phox and are regulated by soluble regulatory proteins: p47^phox, its related organizer NOXO1; p67^phox, its related activator NOXA1; p40^phox; and the small GTPase Rac. Activation of the phagocyte oxidase NOX2 requires p47^phox, p67^phox, and GTP-bound Rac. In addition to these regulators, p40^phox plays a crucial role when NOX2 is activated during phagocytosis. On the other hand, NOX1 activation prefers NOXO1 and NOXA1, although Rac is also involved. NOX3 constitutively produces superoxide, which is enhanced by regulatory proteins such as p47^phox, NOXO1, and p67^phox. Here we describe mechanisms for NOX activation with special attention to the soluble regulatory proteins.

Aromatic Regions Govern the Recognition of NADPH Oxidase Inhibitors as Diapocynin and its Analogues

Oxidative stress is related to the pathogenesis and progress of several human diseases. NADPH oxidase (NOX), and mainly the NOX2 isoform, produces superoxide anions (O₂^•- ). To date, it is known that NOX2 can be inhibited by preventing the assembly of its subunits, p47phox and p22phox. In this work, we analyzed the binding to NOX2 of the apocynin dimer, diapocynin (C1), a known NOX2 inhibitor, and of 18 designed compounds (C2-C19) which have chemical relationships to C1, by in silico methods employing a p47phox structure from the Protein Data Bank (PDB code: 1WLP). C1 and six of the designed compounds were recognized in the region where p22phox binds to p47phox and makes π-π interactions principally with W193, W263, and Y279, which form an aromatic-rich region. C8 was chosen as the best compound according to the in silico studies and was synthesized and evaluated in vitro. C8 was able to prevent the production of reactive oxygen species (ROS) similar to C1. In conclusion, targeting the aromatic region of p47phox through π-interactions is important for inhibiting NOX activity.

CYBA encoding p22(phox), the cytochrome b558 alpha polypeptide: gene structure, expression, role and physiopathology

P22(phox) is a ubiquitous protein encoded by the CYBA gene located on the long arm of chromosome 16 at position 24, containing six exons and spanning 8.5 kb. P22(phox) is a critical component of the superoxide-generating nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs). It is associated with NOX2 to form cytochrome b558 expressed mainly in phagocytes and responsible for the killing of microorganisms when bacterial and fungal infections occur. CYBA mutations lead to one of the autosomal recessive forms of chronic granulomatous disease (AR22(0)CGD) clinically characterized by recurrent and severe infections in early childhood. However, p22(phox) is also the partner of NOX1, NOX3 and NOX4, but not NOX5, which are analogs of NOX2, the first identified member of the NOX family. P22(phox)-NOX complexes have emerged as one of the most relevant sources of reactive oxygen species (ROS) in tissues and cells, and are associated with several diseases such as cardiovascular and cerebrovascular diseases. The p22(phox)-deficient mouse strain nmf333 has made it possible to highlight the role of p22(phox) in the control of inner ear balance in association with NOX3. However, the relevance of p22(phox) for NOX3 function remains uncertain because AR22(0)CGD patients do not suffer from vestibular dysfunction. Finally, a large number of genetic variations of CYBA have been reported, among them the C242T polymorphism, which has been extensively studied in association with coronary artery and heart diseases, but conflicting results continue to be reported.

Crystallographic studies on protein misfolding: Domain swapping and amyloid formation in the SH3 domain

Oligomerization by 3D domain swapping is found in a variety of proteins of diverse size, fold and function. In the early 1960s this phenomenon was postulated for the oligomers of ribonuclease A, but it was not until the 1990s that X-ray diffraction provided the first experimental evidence of this special manner of oligomerization. Nowadays, structural information has allowed the identification of these swapped oligomers in over one hundred proteins. Although the functional relevance of this phenomenon is not clear, this alternative folding of protomers into intertwined oligomers has been related to amyloid formation. Studies on proteins that develop 3D domain swapping might provide some clues on the early stages of amyloid formation. The SH3 domain is a small modular domain that has been used as a model to study the basis of protein folding. Among SH3 domains, the c-Src-SH3 domain emerges as a helpful model to study 3D domain swapping and amyloid formation.

Nox4: a hydrogen peroxide-generating oxygen sensor

Nox4 is an oddity among members of the Nox family of NADPH oxidases [seven isoenzymes that generate reactive oxygen species (ROS) from molecular oxygen] in that it is constitutively active. All other Nox enzymes except for Nox4 require upstream activators, either calcium or organizer/activator subunits (p47(phox), NOXO1/p67(phox), and NOXA1). Nox4 may also be unusual as it reportedly releases hydrogen peroxide (H₂O₂) in contrast to Nox1-Nox3 and Nox5, which release superoxide, although this result is controversial in part because of possible membrane compartmentalization of superoxide, which may prevent detection. Our studies were undertaken (1) to identify the Nox4 ROS product using a membrane-free, partially purified preparation of Nox4 and (2) to test the hypothesis that Nox4 activity is acutely regulated not by activator proteins or calcium, but by cellular pO₂, allowing it to function as an O₂ sensor, the output of which is signaling H₂O₂. We find that approximately 90% of the electron flux through isolated Nox4 produces H₂O₂ and 10% forms superoxide. The kinetic mechanism of H₂O₂ formation is consistent with a mechanism involving binding of one oxygen molecule, which is then sequentially reduced by the heme in two one-electron reduction steps first to form a bound superoxide intermediate and then H₂O₂; kinetics are not consistent with a previously proposed internal superoxide dismutation mechanism involving two oxygen binding/reduction steps for each H₂O₂ formed. Critically, Nox4 has an unusually high Km for oxygen (∼18%), similar to the values of known oxygen-sensing enzymes, compared with a Km of 2-3% for Nox2, the phagocyte NADPH oxidase. This allows Nox4 to generate H₂O₂ as a function of oxygen concentration throughout a physiological range of pO2 values and to respond rapidly to changes in pO₂.

Molecular insights of p47phox phosphorylation dynamics in the regulation of NADPH oxidase activation and superoxide production

Phagocyte superoxide production by a multicomponent NADPH oxidase is important in host defense against microbial invasion. However inappropriate NADPH oxidase activation causes inflammation. Endothelial cells express NADPH oxidase and endothelial oxidative stress due to prolonged NADPH oxidase activation predisposes many diseases. Discovering the mechanism of NADPH oxidase activation is essential for developing novel treatment of these diseases. The p47^phox is a key regulatory subunit of NADPH oxidase; however, due to the lack of full protein structural information, the mechanistic insight of p47^phox phosphorylation in NADPH oxidase activation remains incomplete. Based on crystal structures of three functional domains, we generated a computational structural model of the full p47^phox protein. Using a combination of in silico phosphorylation, molecular dynamics simulation and protein/protein docking, we discovered that the C-terminal tail of p47^phox is critical for stabilizing its autoinhibited structure. Ser-379 phosphorylation disrupts H-bonds that link the C-terminal tail to the autoinhibitory region (AIR) and the tandem Src homology 3 (SH3) domains, allowing the AIR to undergo phosphorylation to expose the SH3 pocket for p22^phox binding. These findings were confirmed by site-directed mutagenesis and gene transfection of p47^phox−/− coronary microvascular cells. Compared with wild-type p47^phox cDNA transfected cells, the single mutation of S379A completely blocked p47^phox membrane translocation, binding to p22^phox and endothelial O₂^⨪ production in response to acute stimulation of PKC. p47^phox C-terminal tail plays a key role in stabilizing intramolecular interactions at rest. Ser-379 phosphorylation is a molecular switch which initiates p47^phox conformational changes and NADPH oxidase-dependent superoxide production by cells.

Conformational change of Sos-derived proline-rich peptide upon binding Grb2 N-terminal SH3 domain probed by NMR

Growth factor receptor-bound protein 2 (Grb2) is a small adapter protein composed of a single SH2 domain flanked by two SH3 domains. The N-terminal SH3 (nSH3) domain of Grb2 binds a proline-rich region present in the guanine nucleotide releasing factor, son of sevenless (Sos). Using NMR relaxation dispersion and chemical shift analysis methods, we investigated the conformational change of the Sos-derived proline-rich peptide during the transition between the free and Grb2 nSH3-bound states. The chemical shift analysis revealed that the peptide does not present a fully random conformation but has a relatively rigid structure. The relaxation dispersion analysis detected conformational exchange of several residues of the peptide upon binding to Grb2 nSH3.

Ethers and esters derived from apocynin avoid the interaction between p47phox and p22phox subunits of NADPH oxidase: evaluation in vitro and in silico

NOX (NADPH oxidase) plays an important role during several pathologies because it produces the superoxide anion (O₂^•−), which reacts with NO (nitric oxide), diminishing its vasodilator effect. Although different isoforms of NOX are expressed in ECs (endothelial cells) of blood vessels, the NOX2 isoform has been considered the principal therapeutic target for vascular diseases because it can be up-regulated by inhibiting the interaction between its p47phox (cytosolic protein) and p22phox (transmembrane protein) subunits. In this research, two ethers, 4-(4-acetyl-2-methoxy-phenoxy)-acetic acid (1) and 4-(4-acetyl-2-methoxy-phenoxy)-butyric acid (2) and two esters, pentanedioic acid mono-(4-acetyl-2-methoxy-phenyl) ester (3) and heptanedioic acid mono-(4-acetyl-2-methoxy-phenyl) ester (4), which are apocynin derivatives were designed, synthesized and evaluated as NOX inhibitors by quantifying O₂^•− production using EPR (electron paramagnetic resonance) measurements. In addition, the antioxidant activity of apocynin and its derivatives were determined. A docking study was used to identify the interactions between the NOX2′s p47phox subunit and apocynin or its derivatives. The results showed that all of the compounds exhibit inhibitory activity on NOX, being 4 the best derivative. However, neither apocynin nor its derivatives were free radical scavengers. On the other hand, the in silico studies demonstrated that the apocynin and its derivatives were recognized by the polybasic SH3A and SH3B domains, which are regions of p47phox that interact with p22phox. Therefore this experimental and theoretical study suggests that compound 4 could prevent the formation of the complex between p47phox and p22phox without needing to be activated by MPO (myeloperoxidase), this being an advantage over apocynin.

A model of interaction between nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and apocynin analogues by docking method

Some apocynin analogues have exhibited outstanding inhibition to NADPH oxidase. In this study, the key interactions between apocynin analogues and NADPH oxidase were analyzed by the docking method. The potential active site was first identified by the SiteID program combining with the key residue CYS378. Afterwards, the compounds in the training set were docked into NADPH oxidase (1K4U) under specific docking constraints to discuss the key interactions between ligands and the receptor. These key interactions were then validated by the consistence between the docking result and the experimental result of the test set. The result reveals that the Pi interaction between apocynin analogues and NADPH oxidase has a direct contribution to inhibition activities, except for H-bond formation and docking score. The key interactions might be valuable to discover and screen apocynin analogues as potent inhibitors of NADPH oxidase.

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.

High-resolution crystal structure of spectrin SH3 domain fused with a proline-rich peptide

A new chimeric protein, named WT-CIIA, was designed by connecting the proline-rich decapeptide PPPVPPYSAG to the C-terminus of the alpha-spectrin SH3 domain through a natural twelve-residue linker to obtain a single-chain model that would imitate intramolecular SH3-ligand interaction. The crystal structure of this fusion protein was determined at 1.7 Å resolution. The asymmetric unit of the crystal contained two SH3 globules contacting with one PPPVPPY fragment located between them. The domains are related by the two-fold non-crystallographic axis and the ligand lies in two opposite orientations with respect to the conservative binding sites of SH3 domains.

Biochemistry, physiology, and pathophysiology of NADPH oxidases in the cardiovascular system

The NADPH oxidase (Nox) enzymes are critical mediators of cardiovascular physiology and pathophysiology. These proteins are expressed in virtually all cardiovascular cells, and regulate such diverse functions as differentiation, proliferation, apoptosis, senescence, inflammatory responses and oxygen sensing. They target a number of important signaling molecules, including kinases, phosphatases, transcription factors, ion channels, and proteins that regulate the cytoskeleton. Nox enzymes have been implicated in many different cardiovascular pathologies: atherosclerosis, hypertension, cardiac hypertrophy and remodeling, angiogenesis and collateral formation, stroke, and heart failure. In this review, we discuss in detail the biochemistry of Nox enzymes expressed in the cardiovascular system (Nox1, 2, 4, and 5), their roles in cardiovascular cell biology, and their contributions to disease development.

Trimer hydroxylated quinone derived from apocynin targets cysteine residues of p47phox preventing the activation of human vascular NADPH oxidase

Enzymatically derived oligophenols from apocynin can be effective inhibitors of human vascular NADPH oxidase (Nox). An isolated trimer hydroxylated quinone (IIIHyQ) has been shown to inhibit endothelial NADPH oxidase with an IC(50) ~30 nM. In vitro studies demonstrated that IIIHyQ is capable of disrupting the interaction between p47(phox) and p22(phox), thereby blocking the activation of the Nox2 isoform. Herein, we report the role of key cysteine residues in p47(phox) as targets for the IIIHyQ. Incubation of p47(phox) with IIIHyQ results in a decrease of ~80% of the protein free cysteine residues; similar results were observed using 1,2- and 1,4-naphthoquinones, whereas apocynin was unreactive. Mutants of p47(phox), in which each Cys was individually replaced by Ala (at residues 111, 196, and 378) or Gly (at residue 98), were generated to evaluate their individual importance in IIIHyQ-mediated inhibition of p47(phox) interaction with p22(phox). Specific Michael addition on Cys196, within the N-SH3 domain, by the IIIHyQ is critical for disrupting the p47(phox)-p22(phox) interaction. When a C196A mutation was tested, the IIIHyQ was unable to disrupt the p47(phox)-p22(phox) interaction. However, the IIIHyQ was effective at disrupting this interaction with the other mutants, displaying IC(50) values (4.9, 21.0, and 2.3μM for the C111A, C378A, and C98G mutants, respectively) comparable to that of wild-type p47(phox).

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.

Combating oxidative stress in vascular disease: NADPH oxidases as therapeutic targets

NADPH oxidases are a family of enzymes that generate reactive oxygen species (ROS). The NOX1 (NADPH oxidase 1) and NOX2 oxidases are the major sources of ROS in the artery wall in conditions such as hypertension, hypercholesterolaemia, diabetes and ageing, and so they are important contributors to the oxidative stress, endothelial dysfunction and vascular inflammation that underlies arterial remodelling and atherogenesis. In this Review, we advance the concept that compared to the use of conventional antioxidants, inhibiting NOX1 and NOX2 oxidases is a superior approach for combating oxidative stress. We briefly describe some common and emerging putative NADPH oxidase inhibitors. In addition, we highlight the crucial role of the NADPH oxidase regulatory subunit, p47phox, in the activity of vascular NOX1 and NOX2 oxidases, and suggest how a better understanding of its specific molecular interactions may enable the development of novel isoform-selective drugs to prevent or treat cardiovascular diseases.

Proline rich polypeptide (PRP-1) increases the superoxide-producing and ferrihemoglobin reducing activities of cytochrome B(558) isoforms from human lymphosarcoma tissue cells

The two cytochromes (cyt) b(558) of acidic nature, one-95-100 kDa and another one, 60-70 kDa were isolated for the first time from the human's lymphosarcoma tissue cells using gel filtration and ion exchange chromatography. These hemoproteins possess NADPH dependent O(2)(-)-producing and ferrihemoglobin-reducing activities. The incubation of neuropeptide PRP-1 (5 μg) with cytochrome b(558), caused elevation of these activities. The gel filtration results indicated possible binding of PRP-1 to these cytochromes b(558). PRP-1 activated both NADPH dependent O(2)(-)-producing and ferriHb-reducing activities of the cyt b(1)(558) and cyt b(2)(558), obtained from human lymphosarcoma tissue cells. One can assume that PRP-1 associated with cyt b(558) on the surface of the tumor cells by increasing both NADPH dependent O(2)(-)-producing and ferriHb-reducing activities of cyt b(558), increases the oxidation- reduction status. Changing the oxidation-reduction status and oxygen homeostasis of the tumor cells by PRP-1 can serve as one of the possible explanation of antitumorigenic effect of this cytokine.

Structural transformation of the tandem ubiquitin-interacting motifs in ataxin-3 and their cooperative interactions with ubiquitin chains

The ubiquitin-interacting motif (UIM) is a short peptide with dual function of binding ubiquitin (Ub) and promoting ubiquitination. We elucidated the structures and dynamics of the tandem UIMs of ataxin-3 (AT3-UIM12) both in free and Ub-bound forms. The solution structure of free AT3-UIM12 consists of two α-helices and a flexible linker, whereas that of the Ub-bound form is much more compact with hydrophobic contacts between the two helices. NMR dynamics indicates that the flexible linker becomes rigid when AT3-UIM12 binds with Ub. Isothermal titration calorimetry and NMR titration demonstrate that AT3-UIM12 binds diUb with two distinct affinities, and the linker plays a critical role in association of the two helices in diUb binding. These results provide an implication that the tandem UIM12 interacts with Ub or diUb in a cooperative manner through an allosteric effect and dynamics change of the linker region, which might be related to its recognitions with various Ub chains and ubiquitinated substrates.

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.

Detection of non-DeltaGT NCF-1 mutations in chronic granulomatous disease

AIMS

Chronic granulomatous disease (CGD) is a rare inherited disorder caused by mutations in the subunits of the NADPH oxidase complex, leaving phagocytes unable to produce superoxide and thereby unable to kill invading microorganisms. A subgroup of CGD patients (approximately 20%) is reported to have mutations in NCF-1 encoding p47-phox, which is part of the cytosolic component of NADPH oxidase. More than 94% of these patients share the same mutation, a 2 bp GT deletion in the GTGT dinucleotide repeat in the start of exon 2. The presence of two pseudogenes more than 98% homologous to the functional NCF-1 has complicated the identification of other mutations in the gene. The aim of this study was to find a general technique for detection of non-GT deletion mutations in the coding region of NCF-1.

RESULTS

A technique involving GeneScan analysis followed by amplification of cDNA with intact dinucleotide repeat was set up and used to identify a novel mutation in exon 7 of NCF-1 in a patient with autosomal recessive CGD, explaining the disease by changing a UGG codon to a premature UGA STOP codon.

CONCLUSION

The method is generally applicable for the detection of NCF-1 mutations in patients with suspected CGD.

Structural, functional, and bioinformatic studies demonstrate the crucial role of an extended peptide binding site for the SH3 domain of yeast Abp1p

SH3 domains, which are among the most frequently occurring protein interaction modules in nature, bind to peptide targets ranging in length from 7 to more than 25 residues. Although the bulk of studies on the peptide binding properties of SH3 domains have focused on interactions with relatively short peptides (less than 10 residues), a number of domains have been recently shown to require much longer sequences for optimal binding affinity. To gain greater insight into the binding mechanism and biological importance of interactions between an SH3 domain and extended peptide sequences, we have investigated interactions of the yeast Abp1p SH3 domain (AbpSH3) with several physiologically relevant 17-residue target peptide sequences. To obtain a molecular model for AbpSH3 interactions, we solved the structure of the AbpSH3 bound to a target peptide from the yeast actin patch kinase, Ark1p. Peptide target complexes from binding partners Scp1p and Sjl2p were also characterized, revealing that the AbpSH3 uses a common extended interface for interaction with these peptides, despite K(d) values for these peptides ranging from 0.3 to 6 mum. Mutagenesis studies demonstrated that residues across the whole 17-residue binding site are important both for maximal in vitro binding affinity and for in vivo function. Sequence conservation analysis revealed that both the AbpSH3 and its extended target sequences are highly conserved across diverse fungal species as well as higher eukaryotes. Our data imply that the AbpSH3 must bind extended target sites to function efficiently inside the cell.

Isoform-selective interaction of the adaptor protein Tks5/FISH with Sos1 and dynamins

The adaptor protein Tks5/FISH (tyrosine kinase substrate 5/five SH3 domains, hereafter termed Tks5) is a crucial component of a protein network that controls the invasiveness of cancer cells and progression of Alzheimer's disease. Tks5 consists of an amino-terminal PX domain that is followed by five SH3 domains (SH3A-E), and two different splice variants are expressed. We identified son of sevenless-1 (Sos1) as a novel binding partner of Tks5 and found colocalization of Tks5 with Sos1 in human epithelial lung carcinoma (A549) cells and in podosomes of Src-transformed NIH 3T3 cells. We observe synergistic binding of SH3A and SH3B to Sos1 when peptide arrays are used, indicating that the tandem SH3A and SH3B domains of Tks5 can potentially bind in a superSH3 binding mode, as was described for the homologous protein p47phox. These results are further corroborated by pull-down assays and isothermal titration calorimetry showing that both intact SH3 domains are required for efficient binding to the entire proline-rich domain of Sos1. The presence of a basic insertion between the SH3A and SH3B domains in the long splice variant of Tks5 decreases the affinity to Sos1 isoforms about 10-fold as determined by analytical ultracentrifugation. Furthermore, it leads to an alteration in the recognition of binding motifs for the interaction with Sos1: While the insertion abrogates the interaction with the majority of peptides derived from the proline-rich domains of Sos1 and dynamin that are recognized by the short splice isoform, it enables binding to a different set of peptides including a sequence comprising the splice insertion in the long isoform of Sos1 (Sos1_2). In the absence of the basic insertion, Tks5 was found to bind a range of Sos1 and dynamin peptides including conventional proline-rich motifs and atypical recognition sequences. Hereby, the tandem SH3 domains in Tks5 employ two distinct types of binding modes: One class of peptides is recognized by single SH3 domains, whereas a second class of peptides requires the presence of both domains to bind synergistically. We conclude that the tandem SH3A and SH3B domains of Tks5 constitute a versatile module for the implementation of isoform-specific protein-protein interactions.

Characterization and expression of NADPH oxidase in LPS-, poly(I:C)- and zymosan-stimulated trout (Oncorhynchus mykiss W.) macrophages

In vertebrates, the generation of superoxide reactive oxygen species (ROS) via activation of the Nox/Duox family of NADPH oxidases is a prototypical feature of the pathogen-induced defensive responses of activated professional phagocytes. To understand the role of the rainbow trout (Oncorhynchus mykiss) Phox oxidase from a phylogenetic and functional perspective we describe the cloning, sequencing and expression analysis of multiple NADPH components in cultured macrophages. Phylogenetic analyses support the notion of the emergence of Phox-related components before the diversification of basal euteleosts and add to the limited collection of teleost NADPH oxidases. Expression studies using lipopolysaccharide, polyinosine-polycytidylic acid and zymosan to mimic the onset of inflammatory responses in trout macrophages suggest differences in regulation of the NADPH complex throughout the maturation/differentiation period of culture and between different treatments.

A region N-terminal to the tandem SH3 domain of p47phox plays a crucial role in the activation of the phagocyte NADPH oxidase

The superoxide-producing NADPH oxidase in phagocytes is crucial for host defence; its catalytic core is the membrane-integrated protein gp91phox [also known as Nox2 (NADPH oxidase 2)], which forms a stable heterodimer with p22phox. Activation of the oxidase requires membrane translocation of the three cytosolic proteins p47phox, p67phox and the small GTPase Rac. At the membrane, these proteins assemble with the gp91phox–p22phox heterodimer and induce a conformational change of gp91phox, leading to superoxide production. p47phox translocates to membranes using its two tandemly arranged SH3 domains, which directly interact with p22phox, whereas p67phox is recruited in a p47phox-dependent manner. In the present study, we show that a short region N-terminal to the bis-SH3 domain is required for activation of the phagocyte NADPH oxidase. Alanine substitution for Ile152 in this region, a residue that is completely conserved during evolution, results in a loss of the ability to activate the oxidase; and the replacement of Thr153 also prevents oxidase activation, but to a lesser extent. In addition, the corresponding isoleucine residue (Ile155) of the p47phox homologue Noxo1 (Nox organizer 1) participates in the activation of non-phagocytic oxidases, such as Nox1 and Nox3. The I152A substitution in p47phox, however, does not affect its interaction with p22phox or with p67phox. Consistent with this, a mutant p47phox (I152A), as well as the wild-type protein, is targeted upon cell stimulation to membranes, and membrane recruitment of p67phox and Rac normally occurs in p47phox (I152A)-expressing cells. Thus the Ile152-containing region of p47phox plays a crucial role in oxidase activation, probably by functioning at a process after oxidase assembly.

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.

Fc gamma R-stimulated activation of the NADPH oxidase: phosphoinositide-binding protein p40phox regulates NADPH oxidase activity after enzyme assembly on the phagosome

The phagocyte NADPH oxidase generates superoxide for microbial killing, and includes a membrane-bound flavocytochrome b(558) and cytosolic p67(phox), p47(phox), and p40(phox) subunits that undergo membrane translocation upon cellular activation. The function of p40(phox), which binds p67(phox) in resting cells, is incompletely understood. Recent studies showed that phagocytosis-induced superoxide production is stimulated by p40(phox) and its binding to phosphatidylinositol-3-phosphate (PI3P), a phosphoinositide enriched in membranes of internalized phagosomes. To better define the role of p40(phox) in FcgammaR-induced oxidase activation, we used immunofluorescence and real-time imaging of FcgammaR-induced phagocytosis. YFP-tagged p67(phox) and p40(phox) translocated to granulocyte phagosomes before phagosome internalization and accumulation of a probe for PI3P. p67(phox) and p47(phox) accumulation on nascent and internalized phagosomes did not require p40(phox) or PI3 kinase activity, although superoxide production before and after phagosome sealing was decreased by mutation of the p40(phox) PI3P-binding domain or wortmannin. Translocation of p40(phox) to nascent phagosomes required binding to p67(phox) but not PI3P, although the loss of PI3P binding reduced p40(phox) retention after phagosome internalization. We conclude that p40(phox) functions primarily to regulate FcgammaR-induced NADPH oxidase activity rather than assembly, and stimulates superoxide production via a PI3P signal that increases after phagosome internalization.