Mutation of putative N-linked glycosylation sites on the human nucleotide receptor P2X7 reveals a key residue important for receptor function.
The nucleotide receptor P2X(7) is an immunomodulatory cation channel and a potential therapeutic target. P2X(7) is expressed in immune cells such as monocytes and macrophages and is activated by extracellular ATP following tissue injury or infection. Ligand binding to P2X(7) can stimulate ERK1/2, the transcription factor CREB, enzymes linked to the production of reactive oxygen species and interleukin-1 isoforms, and the formation of a nonspecific pore. However, little is known about the biochemistry of P2X(7), including whether the receptor is N-linked glycosylated and if this modification affects receptor function. Here we provide evidence that P2X(7) is sensitive to the glycosidases EndoH and PNGase F and that the human receptor appears glycosylated at N187, N202, N213, N241, and N284. Mutation of N187 results in weakened P2X(7) agonist-induced phosphorylation of ERK1/2, CREB, and p90 ribosomal S6 kinase, as well as a decreased level of pore formation. In further support of a role for glycosylation in receptor function, treatment of RAW 264.7 macrophages with the N-linked glycosylation synthesis inhibitor tunicamycin attenuates P2X(7) agonist-induced, but not phorbol ester-induced, ERK1/2 phosphorylation. Interestingly, residue N187 belongs to an N-linked glycosylation consensus sequence found in six of the seven P2X family members, suggesting this site is fundamentally important to P2X receptor function. To address the mechanism whereby N187 mutation attenuates receptor activity, we developed a live cell proteinase K digestion assay that demonstrated altered cell surface expression of P2X(7) N187A. This is the first report to map human P2X(7) glycosylation sites and reveal residue N187 is critical for receptor trafficking and function.
Lenertz
Lisa Y
LY
Department of Biomolecular Chemistry, The University of Wisconsin, Madison, Wisconsin 53706, USA.
Wang
Ziyi
Z
Guadarrama
Arturo
A
Hill
Lindsay M
LM
Gavala
Monica L
ML
Bertics
Paul J
PJ
D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine / Q000235:genetics* / Q000378:metabolism; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D017124:Conserved Sequence; D015536:Down-Regulation / Q000235:genetics; D005110:Extracellular Space / Q000235:genetics; D006031:Glycosylation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D017354:Point Mutation; D020641:Polymorphism, Single Nucleotide; D011499:Protein Processing, Post-Translational / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D058486:Receptors, Purinergic P2X7; D015398:Signal Transduction / Q000235:genetics
C546468:P2RX7 protein, human; C546469:P2rx7 protein, mouse; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D001216:Asparagine
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