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Distinct properties and differential β subunit regulation of two C‐terminal isoforms of the P/Q‐type Ca 2+ ‐channel α 1A subunit
Author(s) -
Sandoz Guillaume,
Bichet Delphine,
Cornet Veronique,
Mori Yasuo,
Felix Ricardo,
De Waard Michel
Publication year - 2001
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.0953-816x.2001.01728.x
Subject(s) - protein subunit , gene isoform , xenopus , alternative splicing , amino acid , chemistry , stereochemistry , biophysics , biology , biochemistry , gene
Two C‐terminal splice variants (BI‐1 and BI‐2, now termed Ca v 2.1a and Ca v 2.1b) of the neuronal voltage‐gated P/Q‐type Ca 2+ channel α 1A pore‐forming subunit have been cloned (Mori et al ., 1991, Nature , 350 , 398–402). BI‐1 and BI‐2 code for proteins of 2273 and 2424 amino acids, respectively, and differ only by their extreme carboxyl‐termini sequences. Here, we show that, in Xenopus oocytes, the two isoforms direct the expression of channels with different properties. Electrophysiological analysis showed that BI‐1 and BI‐2 have peak Ba 2+ currents (I Ba ) at a potential of +30 and +20 mV, respectively. The different C‐terminal sequence (amino acids 2229–2273) of BI‐1 caused a shift in steady‐state inactivation by +10 mV and decreased the proportion of fast component of current inactivation twofold. Likewise, the biophysical changes in I Ba caused by coexpression of the β 4 auxiliary subunit were substantially different in BI‐1‐ and BI‐2‐containing channels in comparison to those induced by β 3 . Several of these differences in β regulation were abolished by deleting the carboxyl‐terminal splicing region. By creating a series of GST fusion proteins, we identified two locations in the C‐terminal (Leu2090–Gly2229 for BI‐1 and BI‐2, and Arg2230–Pro2424 for BI‐2 only) that determine the differential interaction of β 4 with the distinct α 1A isoforms. These interactions appear to favour the binding of β 4 to the AID site, and also the plasma membrane expression of BI‐2. These results demonstrate that the final segment of the C‐terminal affects α 1A channel gating, interaction and regulation with/by the β subunits. The data will have several implications for the understanding of the biophysical effects of many channelopathies in which the carboxyl‐termini of α 1A and β 4 are affected.