Regulation of Derlin-1-mediated degradation of NADPH oxidase partner p22 by thiol modification.

The transmembrane protein p22 heterodimerizes with NADPH oxidase (Nox) 1-4 and is essential for the reactive oxygen species-producing capacity of oxidases. Missense mutations in the p22 gene prevent the formation of phagocytic Nox2-based oxidase, which contributes to host defense. This results in chronic granulomatous disease (CGD), a severe primary immunodeficiency syndrome. In this study, we characterized missense mutations in p22 (L51Q, L52P, E53V, and P55R) in the A22° type (wherein the p22 protein is undetectable) of CGD. We demonstrated that these substitutions enhanced the degradation of the p22 protein in the endoplasmic reticulum (ER) and the binding of p22 to Derlin-1, a key component of ER-associated degradation (ERAD). Therefore, the L-L-E-P sequence is responsible for protein stability in the ER. We observed that the oxidation of the thiol group of Cys-50, which is adjacent to the L-L-E-P sequence, suppressed p22 degradation. However, the suppression effect was markedly attenuated by the serine substitution of Cys-50. Blocking the free thiol of Cys-50 by alkylation or C50S substitution promoted the association of p22 with Derlin-1. Derlin-1 depletion partially suppressed the degradation of p22 mutant proteins. Furthermore, heterodimerization with p22 (C50S) induced rapid degradation of not only Nox2 but also nonphagocytic Nox4 protein, which is responsible for redox signaling. Thus, the redox-sensitive Cys-50 appears to determine whether p22 becomes a target for degradation by the ERAD system through its interaction with Derlin-1.