Molecular Localization of an Ion-Binding Site within the Pore of Mammalian Sodium Channels

• Published in: Science (American Association for the Advancement of Science) 1992-07, Vol.257 (5067), p.248-251
• Main Authors: Backx, Peter H., Yue, David T., Lawrence, John H., Marban, Eduardo, Tomaselli, Gordon F.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; binding; Binding sites; Binding sites (Biochemistry); Binding Sites - genetics; Binding Sites - physiology; Biological and medical sciences; cadmium; Cadmium - pharmacology; Cell physiology; channels; Divalent cations; Electric current; Electric fields; Electric potential; Fundamental and applied biological sciences. Psychology; Ions; localization; Mammalia; Mammals; Membrane and intracellular transports; Membrane Potentials; Molecular and cellular biology; Molecular Sequence Data; Muscles - metabolism; Mutagenesis, Site-Directed; Myocardium - metabolism; Oocytes; Protein isoforms; resistance; sensitivity; sites; Skeletal muscle; sodium; Sodium - metabolism; Sodium channels; Sodium Channels - drug effects; Sodium Channels - metabolism; tetrodotoxin; Tetrodotoxin - pharmacology
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1321496

Sodium channels are the major proteins that underlie excitability in nerve, heart, and skeletal muscle. Chemical reaction rate theory was used to analyze the blockage of single wild-type and mutant sodium channels by cadmium ions. The affinity of cadmium for the native tetrodotoxin (TTX)-resistant cardiac channel was much higher than its affinity for the TTX-sensitive skeletal muscle isoform of the channel (μ l). Mutation of Tyr$^{401}$ to Cys, the corresponding residue in the cardiac sequence, rendered μ l highly susceptible to cadmium blockage but resistant to TTX. The binding site was localized approximately 20% of the distance down the electrical field, thus defining the position of a critical residue within the sodium channel pore.