Contribution of lipid environment to NADPH oxidase activity: Influence of sterol

• p22phox dependence of high-level glycosylation and heme acquisition of Cytb558.
• Phagocyte NADPH oxidase is active at endoplasmic reticulum membranes.
• Sterol membrane content modulates the NADPH oxidase activity.
• Sterols constraint the superoxide anion production rate by Cytb558.
• Potential cholesterol-binding sites in p22phox and gp91phox sequences.

The NADPH-oxidase complex, which plays beneficial or detrimental role in the inflammatory and degenerative diseases, is a membrane multi-subunit complex tightly regulated in order to produce superoxide anions, precursor of oxygen reactive species (ROS), in cells. The flavocytochrome b558 (Cytb558) is the catalytic core of the NADPH oxidase which consists of two membrane proteins gp91phox (highly glycosylated) and p22phox. In this work we took advantage of heterologous yeast cells engineered to express wild-type bovine Cytb558 to analyze the properties of the NADPH oxidase activity during the biosynthesis processing steps of gp91phox and p22phox within endoplasmic reticulum (ER) and plasma membrane (Pmb). Our data showed that, in yeast, the heterodimerization at the endoplasmic reticulum membranes was concomitant with high level glycosylation of gp91phox and the heme acquisition. This study also demonstrated that the phagocyte NADPH oxidase was active at ER membranes and that this activity was surprisingly higher at the ER compared to the Pmb membranes. We have correlated these findings with the presence of sterols in the plasma membranes and their absence in ER membranes. This correlation was confirmed by decreased superoxide anion production rates in proteoliposomes supplemented with ergosterol or cholesterol. Our data support the idea that membrane environment might be determinant for ROS regulation and that sterols could directly interact with the membrane proteins of the NADPH oxidase constraining its capacity to produce superoxide anions.