Supra-Molecular Assemblies of ORAI1 at Rest Precede Local Accumulation into Puncta after Activation |
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Authors: | Diana B Peckys Daniel Gaa Dalia Alansary Barbara A Niemeyer Niels de Jonge |
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Affiliation: | 1.Molecular Biophysics, Center for Integrative Physiology and Molecular Medicine, Saarland University, 66421 Homburg, Germany; (D.B.P.); (D.A.); (B.A.N.);2.INM—Leibniz Institute for New Materials, 66123 Saarbrücken, Germany;3.Department of Physics, Saarland University, 66123 Saarbrücken, Germany |
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Abstract: | The Ca2+ selective channel ORAI1 and endoplasmic reticulum (ER)-resident STIM proteins form the core of the channel complex mediating store operated Ca2+ entry (SOCE). Using liquid phase electron microscopy (LPEM), the distribution of ORAI1 proteins was examined at rest and after SOCE-activation at nanoscale resolution. The analysis of over seven hundred thousand ORAI1 positions revealed a number of ORAI1 channels had formed STIM-independent distinct supra-molecular clusters. Upon SOCE activation and in the presence of STIM proteins, a fraction of ORAI1 assembled in micron-sized two-dimensional structures, such as the known puncta at the ER plasma membrane contact zones, but also in divergent structures such as strands, and ring-like shapes. Our results thus question the hypothesis that stochastically migrating single ORAI1 channels are trapped at regions containing activated STIM, and we propose instead that supra-molecular ORAI1 clusters fulfill an amplifying function for creating dense ORAI1 accumulations upon SOCE-activation. |
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Keywords: | calcium channel protein clusters membrane protein liquid phase electron microscopy single molecule correlative microscopy |
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