Two identical noninteracting sites in an ion channel revealed by proton transfer.
The functional consequences of single proton transfers occurring in the pore of a cyclic nucleotide-gated channel were observed with patch recording techniques. These results led to three conclusions about the chemical nature of ion binding sites in the conduction pathway: The channel contains two identical titratable sites, even though there are more than two (probably four) identical subunits; the sites are formed by glutamate residues that have a pKa (where K(a) is the acid constant) of 7.6; and protonation of one site does not perturb the pKa of the other. These properties point to an unusual arrangement of carboxyl side-chain residues in the pore of a cation channel.
Root
M J
MJ
Department of Neurobiology, Harvard Medical School, Boston, MA 02115.
MacKinnon
R
R
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015220:Calcium Channels / Q000378:metabolism; D002397:Catfishes; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D011522:Protons; D012964:Sodium / Q000378:metabolism; D014981:Xenopus
D015220:Calcium Channels; D007473:Ion Channels; D011522:Protons; D012964:Sodium