Structural basis for EROS binding to human phagocyte NADPH oxidase NOX2

EROS (essential for reactive oxygen species) is a recently identified molecular chaperone of NOX2 (gp91phox), the catalytic subunit of phagocyte NADPH oxidase. Deficiency in NOX2 expression or function due to genetic mutations leads to chronic granulomatous disease (CGD) with recurrent bacterial and fungal infections. To delineate how EROS interacts with NOX2, we solved the cryo-EM structure of the EROS-NOX2-p22phox heterotrimeric complex. EROS binds to NOX2 in plasma membrane through its anti-parallel α-helices H1 and H2, and in cytoplasm through multiple β-strands that form hydrogen bonds with the C terminal fragment of NOX2. EROS binding alters the conformation of the TM2 and TM6 transmembrane helices, increases the distance between the two hemes, and causes dislocation of the binding site for flavin adenine dinucleotide (FAD). EROS colocalizes with NOX2 on cell surface of neutrophil-like HL-60 cells and forms a heterotrimer with mature NOX2-p22phox in transfected cells. Phorbol myristate acetate, an activator of NOX2, induces dissociation of EROS from NOX2 in a NanoLuc complementation assay with concurrent production of superoxide in reconstituted cells. Taken together, these findings provide a structural basis for EROS-NOX2 interaction and suggest a previously unidentified function of EROS in regulating NOX2 activation. ### Competing Interest Statement The authors have declared no competing interest.