[^1]
Gene
[^2]
[XK](/genes/xk)
UniProt
[P27169](https://www.uniprot.org/uniprot/P27169)
Subcellular Localization
Plasma membrane
Protein Family
XK family (Kell blood group)
XK is a membrane protein that partners with the Kell glycoprotein to form the Kell blood group system precursor. The XK/Kell complex functions as a neutral amino acid transporter and is expressed in various tissues including neurons. Mutations in the XK gene cause McLeod syndrome, a rare X-linked neurodegenerative disorder.
XK is a 439 amino acid protein with 10 transmembrane domains. It forms a heterodimeric complex with the Kell glycoprotein (XK/Kell) through disulfide bonds. The protein lacks known enzyme activity but functions as a transporter.
XK plays several important roles in neuronal health:
- Amino acid transport: Facilitates uptake of neutral amino acids across the plasma membrane
- Redox regulation: May participate in cellular oxidative stress responses
- Neuronal development: Important for proper neuronal maturation and maintenance
- Erythrocyte function: In blood cells, the XK/Kell complex maintains erythrocyte shape and integrity
XK mutations cause McLeod syndrome, characterized by:
- Movement disorders: Chorea, dystonia, and parkinsonism
- Cognitive impairment: Progressive dementia in some patients
- Peripheral neuropathy: Sensorimotor neuropathy
- Cardiac arrhythmias: Cardiac involvement can be life-threatening
- Acanthocytosis: Abnormal red blood cell morphology
The neurodegenerative phenotype results from accumulated cellular dysfunction due to impaired amino acid transport and potential oxidative stress.
- Some studies suggest XK variants may modify PD risk
- The protein's role in cellular homeostasis may influence alpha-synuclein pathology
- Gene therapy: XK gene replacement in development
- Symptomatic treatment: Dopaminergic medications for movement symptoms
- Supportive care: Management of cardiac and neurological complications