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Type: Text × Subject: calcium channel ×

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    Supra-Molecular Assemblies of ORAI1 at Rest Precede Local Accumulation into Puncta after Activation
    (Basel : Molecular Diversity Preservation International, 2021) Peckys, Diana B.; Gaa, Daniel; Alansary, Dalia; Niemeyer, Barbara A.; de Jonge, Niels
    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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    The bruchpilot cytomatrix determines the size of the readily releasable pool of synaptic vesicles
    (London : Nature Publishing Group, 2013) Matkovic, Tanja; Siebert, Matthias; Knoche, Elena; Depner, Harald; Mertel, Sara; Owald, David; Schmidt, Manuela; Thomas, Ulrich; Sickmann, Albert; Kamin, Dirk; Hell, Stefan W.; Bürger, Jörg; Hollmann, Christina; Mielke, Thorsten; Wichmann, Carolin; Sigrist, Stephan J.
    Synaptic vesicles (SVs) fuse at a specialized membrane domain called the active zone (AZ), covered by a conserved cytomatrix. How exactly cytomatrix components intersect with SV release remains insufficiently understood. We showed previously that loss of the Drosophila melanogaster ELKS family protein Bruchpilot (BRP) eliminates the cytomatrix (T bar) and declusters Ca2+ channels. In this paper, we explored additional functions of the cytomatrix, starting with the biochemical identification of two BRP isoforms. Both isoforms alternated in a circular array and were important for proper T-bar formation. Basal transmission was decreased in isoform-specific mutants, which we attributed to a reduction in the size of the readily releasable pool (RRP) of SVs. We also found a corresponding reduction in the number of SVs docked close to the remaining cytomatrix. We propose that the macromolecular architecture created by the alternating pattern of the BRP isoforms determines the number of Ca2+ channel-coupled SV release slots available per AZ and thereby sets the size of the RRP.