Dataset Information

Plasticity in Ca2+ selectivity of Orai1/Orai3 heteromeric channel.

ABSTRACT: A general cellular response following depletion of intracellular calcium stores involves activation of store-operated channels (SOCs). While Orai1 forms the native Ca(2+) release-activated Ca(2+) (CRAC) channel in mast and T cells, the molecular architecture of less Ca(2+) selective SOCs is insufficiently defined. Here we present evidence that diminished Ca(2+) selectivity and robust Cs(+) permeation together with a reduced fast inactivation are characteristics of heteromeric Orai1 and Orai3 channels in contrast to their homomeric forms. The first extracellular loop of these Orai isoforms differs by two aspartates replacing glutamates that affect the selectivity. Co-expression of an Orai3 mutant that mimicked the first loop of Orai1 with either Orai1 or Orai3 recovered or decreased Ca(2+) selectivity, respectively. Heteromeric Orai1/3 protein assembly provides a concept for less Ca(2+)-selective SOCs.

SUBMITTER: Schindl R

PROVIDER: S-EPMC2780800 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

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Plasticity in Ca2+ selectivity of Orai1/Orai3 heteromeric channel.

Schindl Rainer R Frischauf Irene I Bergsmann Judith J Muik Martin M Derler Isabella I Lackner Barbara B Groschner Klaus K Romanin Christoph C

Proceedings of the National Academy of Sciences of the United States of America 20091103 46

A general cellular response following depletion of intracellular calcium stores involves activation of store-operated channels (SOCs). While Orai1 forms the native Ca(2+) release-activated Ca(2+) (CRAC) channel in mast and T cells, the molecular architecture of less Ca(2+) selective SOCs is insufficiently defined. Here we present evidence that diminished Ca(2+) selectivity and robust Cs(+) permeation together with a reduced fast inactivation are characteristics of heteromeric Orai1 and Orai3 cha ...[more]

PMID: 19887627

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Project description:Orai1, the pore subunit of Ca(2+) release-activated Ca(2+) channels, has four transmembrane segments (TMs). The first segment, TMI, lines the pore and plays an important role in channel activation and ion permeation. TMIII, on the other hand, does not line the pore but still regulates channel gating and permeation properties. To understand the role of TMIII, we have mutated and characterized several residues in this domain. Mutation of Trp-176 to Cys (W176C) and Gly-183 to Ala (G183A) had dramatic effects. Unlike wild-type channels, which exhibit little outward current and are activated by STIM1, W176C mutant channels exhibited a large outward current at positive potentials and were constitutively active in the absence of STIM1. G183A mutant channels also exhibited substantial outward currents but were active only in the presence of 2-aminoethoxydiphenyl borate (2-APB), irrespective of STIM1. With W176C mutant channels inward, monovalent currents were blocked by Ca(2+) with a high affinity similar to the wild type, but the Ca(2+)-dependent blocking of outward currents differed in the two cases. Although a 50% block of the WT outward current required 250 μm Ca(2+), more than 6 mm was necessary to have the same effect on W176C mutant channels. In the presence of extracellular Ca(2+), W176C and G183A outward currents developed slowly in a voltage-dependent manner, whereas they developed almost instantaneously in the absence of Ca(2+). These changes in permeation and gating properties mimic the changes induced by mutations of Glu-190 in TMIII and Asp-110/Asp-112 in the TMI/TMII loop. On the basis of these data, we propose that TMIII maintains negatively charged residues at or near the selectivity filter in a conformation that facilitates Ca(2+) inward currents and prevents outward currents of monovalent cations. In addition, to controlling selectivity, TMIII may also stabilize channel gating in a closed state in the absence of STIM1 in a Trp-176-dependent manner.

Dataset Information

Plasticity in Ca2+ selectivity of Orai1/Orai3 heteromeric channel.

Publications

Plasticity in Ca2+ selectivity of Orai1/Orai3 heteromeric channel.

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