TY - JOUR
T1 - Molecular Determinants of Ion Permeation and Selectivity in Inositol 1,4,5-Trisphosphate Receptor Ca2+ Channels
AU - Boehning, Darren
AU - Mak, Don On Daniel
AU - Kevin Foskett, J.
AU - Joseph, Suresh K.
PY - 2001
Y1 - 2001
N2 - We tested the hypothesis that key residues in a putative intraluminal loop contribute to determination of ion permeation through the intracellular Ca release channel (inositol 1,4,5-trisphosphate receptors (IP3Rs)) that is gated by the second messenger inositol 1,4,5-trisphophate (IP3). To accomplish this, we mutated residues within the putative pore forming region of the channel and analyzed the functional properties of mutant channels using a 45Ca flux assay and single channel electrophysiological analyses. Two IP3R mutations, V2548I and D2550E, retained the ability to release 45Ca2+ in response to IP3. When analyzed at the single channel level; both recombinant channels had IP3-dependent open probabilities similar to those observed in wild-type channels. The mutation V2548I resulted in channels that exhibited a larger K+ conductance (489 ±13 picosiemens (pS) for V2548I versus 364 ±5 pS for wildtype), but retained a Ca2+ selectivity similar to wild-type channels (PCa2+:PK+ ∼ 4:1). Conversely, D2550E channels were nonselective for Ca2+ over K+(PCa2+:PK+ ∼ 0.6:1), while the K+ conductance was effectively unchanged (391 ± 4 pS). These results suggest that amino acid residues Val2548 and Asp2550 contribute to the ion conduction pathway. We propose that the pore of IP3R channels has two distinct sites that control monovalent cation permeation (Val2548) and Ca2+ selectivity (Asp2550).
AB - We tested the hypothesis that key residues in a putative intraluminal loop contribute to determination of ion permeation through the intracellular Ca release channel (inositol 1,4,5-trisphosphate receptors (IP3Rs)) that is gated by the second messenger inositol 1,4,5-trisphophate (IP3). To accomplish this, we mutated residues within the putative pore forming region of the channel and analyzed the functional properties of mutant channels using a 45Ca flux assay and single channel electrophysiological analyses. Two IP3R mutations, V2548I and D2550E, retained the ability to release 45Ca2+ in response to IP3. When analyzed at the single channel level; both recombinant channels had IP3-dependent open probabilities similar to those observed in wild-type channels. The mutation V2548I resulted in channels that exhibited a larger K+ conductance (489 ±13 picosiemens (pS) for V2548I versus 364 ±5 pS for wildtype), but retained a Ca2+ selectivity similar to wild-type channels (PCa2+:PK+ ∼ 4:1). Conversely, D2550E channels were nonselective for Ca2+ over K+(PCa2+:PK+ ∼ 0.6:1), while the K+ conductance was effectively unchanged (391 ± 4 pS). These results suggest that amino acid residues Val2548 and Asp2550 contribute to the ion conduction pathway. We propose that the pore of IP3R channels has two distinct sites that control monovalent cation permeation (Val2548) and Ca2+ selectivity (Asp2550).
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U2 - 10.1074/jbc.c100094200
DO - 10.1074/jbc.c100094200
M3 - Article
C2 - 11278266
AN - SCOPUS:0035957945
SN - 0021-9258
VL - 276
SP - 13509
EP - 13512
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 17
ER -