Ca2+ channel selectivity at a single locus for high-affinity Ca2+ interactions.
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.
Ellinor
P T
PT
Department of Molecular and Cellular Physiology, Beckman Center, Stanford University Medical Center, California 94305, USA.
Yang
J
J
Sather
W A
WA
Zhang
J F
JF
Tsien
R W
RW
D000409:Alanine; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D002413:Cations, Divalent; D004563:Electrochemistry; D004594:Electrophysiology; D005260:Female; D018014:Gene Transfer Techniques; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine; D016296:Mutagenesis; D009206:Myocardium / Q000737:chemistry; D009865:Oocytes / Q000502:physiology; D017354:Point Mutation; D012333:RNA, Messenger / Q000235:genetics; D011817:Rabbits; D014982:Xenopus laevis
D015220:Calcium Channels; D002413:Cations, Divalent; D012333:RNA, Messenger; D005973:Glutamine; D018698:Glutamic Acid; D000409:Alanine; D002118:Calcium