The aromatic binding site for tetraethylammonium ion on potassium channels.
K+ channels are quite variable in their sensitivity to the pore-blocking agent tetraethylammonium ion (TEA) when it is applied to the extracellular side of the membrane. A Shaker K+ channel can be made highly sensitive by introducing a tyrosine (or phenylalanine) at residue 449 in each of the four subunits. A shift in the voltage dependence of blockade indicates that TEA senses a smaller fraction of the transmembrane electric field in the highly sensitive channels. There is a linear relationship between the free energy for TEA blockade and the number of subunits (zero, two, or four) containing tyrosine at 449, as if these four residues interact simultaneously with a TEA molecule to produce a high affinity binding site. The temperature dependence of blockade suggests that the interaction is not purely hydrophobic. These findings are consistent with a TEA-binding site formed by a bracelet of pore-lining aromatic residues. The center of the bracelet could bind a TEA molecule through a cation-pi orbital interaction.
Heginbotham
L
L
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
MacKinnon
R
R
D000818:Animals; D001665:Binding Sites; D004252:DNA Mutational Analysis; D004331:Drosophila melanogaster; D004553:Electric Conductivity; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008564:Membrane Potentials; D010649:Phenylalanine / Q000737:chemistry; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins; D013757:Tetraethylammonium Compounds / Q000378:metabolism*; D013816:Thermodynamics; D014443:Tyrosine / Q000737:chemistry
D015221:Potassium Channels; D011994:Recombinant Proteins; D013757:Tetraethylammonium Compounds; D014443:Tyrosine; D010649:Phenylalanine