The NADPH‐Dependent Oxidase of Phagocytes

Abstract

Polymorphonuclear leukocytes (PMNs) represent a prominent cellular element in the innate immune system, serving to ingest exogenous particles and microbes and to kill phagocytosed microorganisms. The microbicidal activity of PMNs depends on the interactions of a broad array of potent systems, including relatively stable degradative proteins as well as labile reactive radicals. These systems can be categorized as oxygen-dependent and nonoxidative mechanisms, although the physiologically relative activity depends on the precisely orchestrated interplay between both systems. The enzyme complex responsible for the activity of the oxygen-dependent system is the respiratory burst oxidase and its important contribution to host defense is best illustrated by the frequent and severe infections seen in individuals whose PMNs lack oxidase activity, namely patients with chronic granulomatous disease (CGD). Multiple elements comprise the oxygen-dependent system, and significant advances have been made in the past decade in understanding the protein components of the respiratory burst oxidase, their subcellular distribution in resting PMNs, and their agonist-dependent assembly into a functional system at phagosomal and plasma membranes. In parallel, substantial insights into the molecular bases of CGD have likewise been made. Nonetheless there remain significant gaps in our understanding of the precise functional contributions of particular components of the system, the molecular mechanisms that regulate their coordinated assembly, and the role of related proteins in nonphagocytic cells.

Novel Human Homologues of p47 and p67 Participate in Activation of Superoxide-producing NADPH Oxidases

“…The activation of cytochrome b 558 requires stimulus-induced membrane translocation of cytosolic proteins including the small GTPase Rac and the two specialized cytosolic proteins p67 phox and p47 phox , each containing two SH3 domains (3)(4)(5)(6)(7)(8)(9). In this process, p47 phox translocates to the membrane by itself, whereas p67 phox is recruited via p47 phox (15,16); they constitutively associate via a tail-to-tail interaction (17)(18)(19).…”

“…Hence, the formation of the active phagocyte oxidase in cells requires the five proteins, namely gp91 phox , p22 phox , p67 phox , p47 phox , and Rac in the GTP-bound state; chronic granulomatous disease is caused by a defect of any of the genes encoding these proteins except Rac (9). The active oxidase can be formed in a cell-free system reconstituted with the purified proteins described above and anionic amphiphiles such as arachidonic acid (3)(4)(5)(6)(7)(8)(9). In the presence of excess amounts of p67 phox and Rac, however, p47 phox is not essential for the cell-free activation of the oxidase (33)(34)(35).…”

“…The mammalian members occur in various types of cells. The founder Nox protein gp91 phox (Nox2) is predominantly expressed in professional phagocytes such as neutrophils and plays a crucial role in host defense against microbial infection (3)(4)(5)(6)(7)(8)(9). On the other hand, Nox1 and Nox4 are abundant in epithelial cells in colon and kidney (10 -14), respectively, but their biological roles are not well understood at present.…”

“…On the other hand, Nox1 and Nox4 are abundant in epithelial cells in colon and kidney (10 -14), respectively, but their biological roles are not well understood at present. The Nox oxidases are membrane-integrated proteins containing a complete electron-transferring apparatus (from NADPH to molecular oxygen) with binding sites for heme, FAD, and NADPH (3)(4)(5)(6)(7)(8)(9). In phagocytes, gp91 phox is complexed with p22 phox to form flavocytochrome b 558 .…”

Functional Epitope on Human Neutrophil Flavocytochrome b558

“…T he human phagocyte NADPH oxidase is a multisubunit enzyme complex that produces the superoxide anion (O 2 Ϫ ) for the destruction of pathogens (1). This system is activated by a variety of stimuli and exerts toxic effects in most inflammatory processes (2).…”