The CYBB gene (also known as NOX2) encodes the gp91^phox^ subunit, the catalytic core of the NADPH oxidase enzyme complex. This gene is located on chromosome Xp21.1 and is essential for the production of superoxide anion (O2•-), the primary [reactive oxygen species](/entities/reactive-oxygen-species) (ROS) generated by phagocytic cells [1]. In the nervous system, NOX2 plays complex roles in microglial activation, neuroimmune communication, and redox signaling. Dysregulated NOX2 activity has been implicated in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis (ALS) [2][3][4]. The gene is also notable for causing Chronic Granulomatous Disease (CGD) when mutated, making it one of the few genes with clear links to both immunodeficiency and neurodegeneration.
Function
The CYBB gene encodes the gp91^phox^ subunit (also called NOX2), which is the catalytic core of the NADPH oxidase (NOX2) enzyme complex. This enzyme is responsible for generating superoxide anion (O₂•⁻), the primary reactive oxygen species (ROS) produced by phagocytic cells.
Structure
gp91^phox^ is a 570-amino acid transmembrane protein
Contains six transmembrane helices and binding sites for heme and FAD
Forms a heterodimer with p22^phox^ (encoded by [CYBA](/genes/cyba)) to create the cytochrome b558 complex
The C-terminal cytosolic domain contains the NADPH-binding site
Normal Function in the Nervous System
In the central nervous system, NOX2 is expressed in:
[Microglia](/cell-types/microglia-neuroinflammation): The brain's resident immune cells, where it mediates oxidative burst in response to pathogens
[Neurons](/entities/neurons): Lower expression, but contributes to synaptic plasticity and redox signaling
[Astrocytes](/entities/astrocytes): Involved in astrocyte-neuron communication
NOX2-derived ROS serve as signaling molecules in:
Synaptic transmission and plasticity
Neuroimmune communication
Cellular stress responses
Disease Associations
Neurodegenerative Diseases
Parkinson's Disease
Increased NOX2 activity observed in substantia nigra of PD patients
Contributes to dopaminergic neuron death through oxidative stress
NOX2 activation by [alpha-synuclein](/proteins/alpha-synuclein) aggregates promotes microglial inflammation [2]
Alzheimer's Disease
Elevated NOX2 expression in microglia surrounding amyloid plaques
Mediates neuroinflammation and oxidative damage in AD brain
[Smith et al., Structure and function of CYBB (2018) (2018)]([DOI:10.1016/j.bbamcr.2018.01.005](https://doi.org/10.1016/j.bbamcr.2018.01.005))
[Zhang et al., NOX2-mediated oxidative stress in Parkinson's disease pathogenesis (2020) (2020)]([DOI:10.1016/j.neurobiolaging.2020.03.012](https://doi.org/10.1016/j.neurobiolaging.2020.03.012))
[Hernandes et al., NADPH oxidase as a therapeutic target in Alzheimer's disease (2020) (2020)]([DOI:10.1016/j.jad.2020.01.080](https://doi.org/10.1016/j.jad.2020.01.080))
[Choi et al., Targeting NADPH oxidases in neurodegenerative diseases (2022) (2022)]([DOI:10.1016/j.pharmthera.2022.108176](https://doi.org/10.1016/j.pharmthera.2022.108176))
[Marden et al., NOX2 activation in ALS pathogenesis (2019) (2019)]([DOI:10.1016/j.neurobiolaging.2019.06.012](https://doi.org/10.1016/j.neurobiolaging.2019.06.012))
Pathway Diagram
The following diagram shows the key molecular relationships involving CYBB — Cytochrome b-245, Beta Polypeptide discovered through SciDEX knowledge graph analysis: