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Ca2+ channel selectivity at a single locus for high-affinity Ca2+ interactions.

Neuron

Female, Animals, Binding Sites, Calcium, metabolism, Calcium Channels, chemistry, genetics, physiology, Cations, Divalent, Electrochemistry, Electrophysiology, Alanine, Gene Transfer Techniques, Glutamic Acid, Glutamine, Mutagenesis, Myocardium, Oocytes, Point Mutation, RNA, Messenger, Rabbits, Xenopus laevis

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      Abstract

      Ca2+ channels display remarkable selectivity and permeability, traditionally attributed to multiple, discrete Ca2+ binding sites lining the pore. Each of the four pore-forming segments of Ca2+ channel alpha 1 subunits contains a glutamate residue that contributes to high-affinity Ca2+ interactions. Replacement of all four P-region glutamates with glutamine or alanine abolished micromolar Ca2+ block of monovalent current without revealing any additional independent high-affinity Ca2+ binding site. Pairwise replacements of the four glutamates excluded the hypothesis that they form two independent high-affinity sites. Systematic alterations of side-chain length, charge, and polarity by glutamate replacement with aspartate, glutamine, or alanine weakened the Ca2+ interaction, with considerable asymmetry from one repeat to another. The P-region glutamate in repeat I was unusual in its sensitivity to aspartate replacement but not glutamine substitution. While all four glutamates cooperate in supporting high-affinity interactions with single Ca2+ ions, they also influence the interaction between multiple divalent cations.

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      7576655

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