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Table 2 Characteristics of the Kell system

From: Chronic granulomatous disease, the McLeod phenotype and the contiguous gene deletion syndrome-a review

Kell protein 93 kDa type II membrane glycoprotein
Short N-terminal intracellular segment with one cysteine residue
Single transmembrane section
Large extracellular domain (665 amino acids with 15 cysteine residues)
One cysteine residue (Cys72) in extracellular domain binds XK protein
Homology to certain zinc endoproteases
Demonstrates endothelin-3 converting enzymatic activity
Encoded by the KEL gene (7q33)
K0 (null) RBC lack Kell antigens but have enhance XK activity
KEL gene is inherited autosomally
XK protein Molecular weight of 50.9 kDa
10 transmembrane segments
Short N-terminal domain (intracellular)
Large C-terminal domain (intracellular)
A large hydrophilic loop (Figure 3)
Single cysteine residue that binds covalently to Cys72 on Kell
Loss of XK leads to McLeod syndrome that has X-linked inheritance