The superoxide-generating NADPH oxidase: structural aspects and activation mechanism

Abstract

Flavocytochrome b558 is the catalytic core of the respiratory-burst oxidase, an enzyme complex that catalyzes the NADPH-dependent reduction of O2 into the superoxide anion O2 in phagocytic cells. Flavocytochrome b558 is anchored in the plasma membrane. It is a heterodimer that consists of a large glycoprotein gp91phox (phox forphagocyte oxidase) (beta subunit) and a small protein p22phox (alpha subunit). The other components of the respiratory-burst oxidase are water-soluble proteins of cytosolic origin, namely p67phox, p47phox, p40phox and Rac. Upon cell stimulation, they assemble with the membrane-bound flavocytochrome b558 which becomes activated and generates O2-. A defect in any of the genes encoding gp91phox, p22phox, p67phox or p47phox results in chronic granulomatous disease, a genetic disorder characterized by severe and recurrent infections, illustrating the role of O2- and the derived metabolites H2O2 and HOCl in host defense against invading microorganisms. The electron carriers, FAD and hemes b, and the binding site for NADPH are confined to the gp91phox subunit of flavocytochrome b558. The p22phox subunit serves as a docking site for the cytoso lic phox proteins. This review provides an overview of current knowledge on the structural organization of the O2(-)-generating flavocytochrome b558, its kinetics, its mechanism of activation and the regulation of its biosynthesis. Homologues of gp91phox, called Nox and Duox, are present in a large variety of non-phagocytic cells. They exhibit modest O2(-)-generating oxidase activity, and some act as proton channels. Their role in various aspects of signal transduction is currently under investigation and is briefly discussed.

NADPH oxidase of human dendritic cells: Role in Candida albicans killing and regulation by interferons, dectin‐1 and CD206

“…It is worth to point out that, although it is not a physiological agonist, PMA directly activates the protein kinase C-dependent phosphorylation of NADPH oxidase components, thus reproducing the final step of NADPH oxidase activation by a large number of physiological stimulators of this enzyme [11]. DC pretreatment with IFN-a or IFN-c increases both the PMA-dependent and the poor PMA-independent fungicidal activity.…”

“…Fig. 2F, G shows that Candida affects the PMA-induced p47phox association with DC plasma membrane, thus hampering the assembly of NADPH oxidase components leading to O 2 -production [10,11].…”

“…ROS produced by NADPH oxidase of leukocytes are involved in pathogen killing, as demonstrated by the recurrent infections affecting individuals with chronic granulomatous disease, an inherited disorder in which the enzyme is not functional [10,11], but are also recognized as signaling molecules [12]. We previously showed that NADPH oxidase is not involved in DC differentiation, LPS-induced maturation, cytokine production and induction of T cell proliferation, but is required for DC killing of intracellular bacteria [9].…”

“…In peripheral tissues, immature DC capture antigens by specialized receptors, undergo maturation and migrate to lymphoid organs where they present antigens to naive T cells [1][2][3][4]. Moreover, DC produce cytotoxic molecules limiting pathogen replication [5][6][7][8].Recently, we reported that human monocyte-derived DC express NADPH oxidase [9], the enzyme of leukocytes responsible for ROS production, whose activation requires the association between cytosolic (p47phox, p67phox, p40phox, p21rac) and membrane (gp91phox, p22phox) components [10,11]. ROS produced by NADPH oxidase of leukocytes are involved in pathogen killing, as demonstrated by the recurrent infections affecting individuals with chronic granulomatous disease, an inherited disorder in which the enzyme is not functional [10,11], but are also recognized as signaling molecules [12].…”

“…Fig. 2F, G shows that Candida affects the PMA-induced p47phox association with DC plasma membrane, thus hampering the assembly of NADPH oxidase components leading to O 2 -production [10,11].NADPH oxidase is involved in Candida-killing activity of DC Leukocytes kill Candida essentially via oxygen-dependent mechanisms [29,30]. We then investigated whether NADPH oxidase is involved in Candida-killing activity of DC.…”