Ectodomain Lysines and Suramin Block of P2X1 Receptors

• Published in: The Journal of biological chemistry Vol. 283; no. 44; pp. 29841 - 29846
• Main Authors: Sim, Joan A., Broomhead, Helen E., North, R. Alan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 31-10-2008; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Animals; Benzenesulfonates - pharmacology; Cell Line; Humans; Kidney - embryology; Lysine - chemistry; Mice; Molecular Basis of Cell and Developmental Biology; Molecular Sequence Data; Muscle, Smooth - metabolism; Patch-Clamp Techniques; Protein Structure, Tertiary; Receptors, Purinergic P2 - chemistry; Receptors, Purinergic P2 - metabolism; Receptors, Purinergic P2X; Sequence Homology, Amino Acid; Suramin - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M802523200

P2X1 receptors belong to a family of cation channels gated by extracellular ATP; they are found inter alia in smooth muscle, platelets, and immune cells. Suramin has been widely used as an antagonist at P2X receptors, and its analog 4,4′,4″,4‴-[carbonylbis(imino-5,1,3-benzenetriylbis(carbonylimino))] tetrakis-benzene-1,3-disulfonic acid (NF449) is selective for the P2X1 subtype. Human and mouse P2X1 receptors were expressed in human embryonic kidney cells, and membrane currents evoked by ATP were recorded. ATP (10 nm to 100 μm) was applied only once to each cell, to avoid the profound desensitization exhibited by P2X1 receptors. Suramin (10 μm) and NF449 (3–300 nm) effectively blocked the human receptor. Suramin had little effect on the mouse receptor. Suramin and NF449 are polysulfonates, with six and eight negative charges, respectively. We hypothesized that species differences might result from differences in positive residues presented by the large receptor ectodomain. Four lysines in the human sequence (Lys111, Lys127, Lys138, and Lys148) were changed individually and together to their counterparts in the mouse sequence. The substitution K138E, either alone or together with K111Q, K127Q, and K148N, reduced the sensitivity to block by both suramin and NF449. Conversely, when lysine was introduced into the mouse receptor, the sensitivity to block by suramin and NF449 was much increased for E138K, but not for Q111K, Q127K, or N148K. The results explain the marked species difference in antagonist sensitivity and identify an ectodomain lysine residue that plays a key role in the binding of both suramin and NF449 to P2X1 receptors.