Cysteine Substitution Mutagenesis and the Effects of Methanethiosulfonate Reagents at P2X2 and P2X4 Receptors Support a Core Common Mode of ATP Action at P2X Receptors

• Published in: The Journal of biological chemistry 2008-07, Vol.283 (29), p.20126-20136
• Main Authors: Roberts, Jonathan A., Digby, Helen R., Kara, Madina, Ajouz, Sam El, Sutcliffe, Michael J., Evans, Richard J.
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - pharmacology; Amino Acid Sequence; Animals; Conserved Sequence; Cysteine - genetics; Cysteine - metabolism; Electrophysiology; Female; Humans; Mechanisms of Signal Transduction; Mesylates - pharmacology; Molecular Sequence Data; Mutation - genetics; Oocytes - drug effects; Patch-Clamp Techniques; Receptors, Purinergic P2 - chemistry; Receptors, Purinergic P2 - genetics; Receptors, Purinergic P2 - metabolism; Receptors, Purinergic P2X2; Receptors, Purinergic P2X4; Sequence Alignment; Xenopus laevis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M800294200

The agonist binding site of ATP-gated P2X receptors is distinct from other ATP-binding proteins. Mutagenesis on P2X1 receptors of conserved residues in mammalian P2X receptors has established the paradigm that three lysine residues, as well as FT and NFR motifs, play an important role in mediating ATP action. In this study we have determined whether cysteine substitution mutations of equivalent residues in P2X2 and P2X4 receptors have similar effects and if these mutant receptors can be regulated by charged methanethiosulfonate (MTS) compounds. All the mutants (except the P2X2 K69C and K71C that were expressed, but non-functional) showed a significant decrease in ATP potency, with >300-fold decreases for mutants of the conserved asparagine, arginine, and lysine residues close to the end of the extracellular loop. MTS reagents had no effect at the phenylalanine of the FT motif, in contrast, cysteine mutation of the threonine was sensitive to MTS reagents and suggested a role of this residue in ATP action. The lysine-substituted receptors were sensitive to the charge of the MTS reagent consistent with the importance of positive charge at this position for coordination of the negatively charged phosphate of ATP. At the NFR motif the asparagine and arginine residues were sensitive to MTS reagents, whereas the phenylalanine was either unaffected or showed only a small decrease. These results support a common site of ATP action at P2X receptors and suggest that non-conserved residues also play a regulatory role in agonist action.