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STIM1/Orai1 coiled-coil interplay in the regulation of store-operated calcium entry.

Stathopulos PB, Schindl R, Fahrner M, Zheng L, Gasmi-Seabrook GM, Muik M, Romanin C, Ikura M - Nat Commun (2013)

Bottom Line: STIM1 mutants disrupting CC1:CC1' interactions attenuate, while variants promoting CC1 stability spontaneously activate Orai1 currents.CC2 mutations cause remarkable variability in Orai1 activation because of a dual function in binding Orai1 and autoinhibiting STIM1 oligomerization via interactions with CC3.We conclude that SOCE is activated through dynamic interplay between STIM1 and Orai1 helices.

View Article: PubMed Central - PubMed

Affiliation: University Health Network and Department of Medical Biophysics, Campbell Family Cancer Research Institute, Ontario Cancer Institute, University of Toronto, Room 4-804, MaRS TMDT, 101 College Street, Toronto, Ontario, Canada M5G 1L7.

ABSTRACT
Orai1 calcium channels in the plasma membrane are activated by stromal interaction molecule-1 (STIM1), an endoplasmic reticulum calcium sensor, to mediate store-operated calcium entry (SOCE). The cytosolic region of STIM1 contains a long putative coiled-coil (CC)1 segment and shorter CC2 and CC3 domains. Here we present solution nuclear magnetic resonance structures of a trypsin-resistant CC1-CC2 fragment in the apo and Orai1-bound states. Each CC1-CC2 subunit forms a U-shaped structure that homodimerizes through antiparallel interactions between equivalent α-helices. The CC2:CC2' helix pair clamps two identical acidic Orai1 C-terminal helices at opposite ends of a hydrophobic/basic STIM-Orai association pocket. STIM1 mutants disrupting CC1:CC1' interactions attenuate, while variants promoting CC1 stability spontaneously activate Orai1 currents. CC2 mutations cause remarkable variability in Orai1 activation because of a dual function in binding Orai1 and autoinhibiting STIM1 oligomerization via interactions with CC3. We conclude that SOCE is activated through dynamic interplay between STIM1 and Orai1 helices.

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Docking of CC1[TM-distal]-CC2 on the Orai hexamera, Structural homology between D. melanogaster Orai and human Orai1 C272-292. The D. melanogaster Orai dimer (top) shows an antiparallel C-terminal configuration (yellow) highly homologous to human Orai1 C272-292 (bottom; yellow). The analogous interhelix angles indicated (broken curved lines). b, Docking of CC1[TM-distal]-CC2 onto hexameric D. melanogaster Orai. The Orai1 C272-292 helices within the CC1[TM-distal]-CC2 complex were structurally aligned through sequentially similar regions in each D. melanogaster Orai dimer. CC3 locations are inferred from the position of the α2 C-termini. The Orai dimer unit is indicated (broken black box). c, Sequence alignment of D. melanogaster Orai and H. sapiens Orai1 C-terminal residues. The H. sapiens Orai1 C272-292 residues and the homologous residues visible in the D. melanogaster crystal structure are yellow. The boxed residues indicate the structurally aligned regions.
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Figure 4: Docking of CC1[TM-distal]-CC2 on the Orai hexamera, Structural homology between D. melanogaster Orai and human Orai1 C272-292. The D. melanogaster Orai dimer (top) shows an antiparallel C-terminal configuration (yellow) highly homologous to human Orai1 C272-292 (bottom; yellow). The analogous interhelix angles indicated (broken curved lines). b, Docking of CC1[TM-distal]-CC2 onto hexameric D. melanogaster Orai. The Orai1 C272-292 helices within the CC1[TM-distal]-CC2 complex were structurally aligned through sequentially similar regions in each D. melanogaster Orai dimer. CC3 locations are inferred from the position of the α2 C-termini. The Orai dimer unit is indicated (broken black box). c, Sequence alignment of D. melanogaster Orai and H. sapiens Orai1 C-terminal residues. The H. sapiens Orai1 C272-292 residues and the homologous residues visible in the D. melanogaster crystal structure are yellow. The boxed residues indicate the structurally aligned regions.

Mentions: Recently, Drosophila melanogaster Orai was crystallized in a hexameric conformation with individual dimers stabilized through antiparallel CC interactions between the cytosolic C-terminal helices 25. Remarkably, the antiparallel configuration of the Orai C-terminal helices in D. melanogaster appear primed for an interaction with STIM, highly analogous to the one elucidated in our human STIM1 CC1[TM-distal]-CC2:Orai1 C272-292 complex structure (Fig. 4a). The interhelix angle between the two interacting D. melanogaster Orai C-terminal helices (i.e. 152°) is very similar to the angle observed in our human complex structure (i.e. 136°) (Fig. 4a). Docking of three dimer structures of CC1[TM-distal]-CC2:Orai1 C272-292 onto the Orai hexamer by structurally aligning the common Orai C-terminal regions (Fig. 4b and 4c) confirms the noteworthy structural compatibility. Specifically, the N-termini of CC1[TM-distal]-CC2, indicating the positions of CC1[TM-proximal], are directed away from the cytosolic channel face toward the ER membrane; further, the C-termini of CC1[TM-distal]-CC2, marking the locations of CC3, are adjacent to the C-termini from neighbouring CC1[TM-distal]-CC2 dimers and compatible with homotypic oligomerization of CC1[TM-distal]-CC2 via CC3 interactions into a required functional stoichiometry (Fig. 4b).


STIM1/Orai1 coiled-coil interplay in the regulation of store-operated calcium entry.

Stathopulos PB, Schindl R, Fahrner M, Zheng L, Gasmi-Seabrook GM, Muik M, Romanin C, Ikura M - Nat Commun (2013)

Docking of CC1[TM-distal]-CC2 on the Orai hexamera, Structural homology between D. melanogaster Orai and human Orai1 C272-292. The D. melanogaster Orai dimer (top) shows an antiparallel C-terminal configuration (yellow) highly homologous to human Orai1 C272-292 (bottom; yellow). The analogous interhelix angles indicated (broken curved lines). b, Docking of CC1[TM-distal]-CC2 onto hexameric D. melanogaster Orai. The Orai1 C272-292 helices within the CC1[TM-distal]-CC2 complex were structurally aligned through sequentially similar regions in each D. melanogaster Orai dimer. CC3 locations are inferred from the position of the α2 C-termini. The Orai dimer unit is indicated (broken black box). c, Sequence alignment of D. melanogaster Orai and H. sapiens Orai1 C-terminal residues. The H. sapiens Orai1 C272-292 residues and the homologous residues visible in the D. melanogaster crystal structure are yellow. The boxed residues indicate the structurally aligned regions.
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Figure 4: Docking of CC1[TM-distal]-CC2 on the Orai hexamera, Structural homology between D. melanogaster Orai and human Orai1 C272-292. The D. melanogaster Orai dimer (top) shows an antiparallel C-terminal configuration (yellow) highly homologous to human Orai1 C272-292 (bottom; yellow). The analogous interhelix angles indicated (broken curved lines). b, Docking of CC1[TM-distal]-CC2 onto hexameric D. melanogaster Orai. The Orai1 C272-292 helices within the CC1[TM-distal]-CC2 complex were structurally aligned through sequentially similar regions in each D. melanogaster Orai dimer. CC3 locations are inferred from the position of the α2 C-termini. The Orai dimer unit is indicated (broken black box). c, Sequence alignment of D. melanogaster Orai and H. sapiens Orai1 C-terminal residues. The H. sapiens Orai1 C272-292 residues and the homologous residues visible in the D. melanogaster crystal structure are yellow. The boxed residues indicate the structurally aligned regions.
Mentions: Recently, Drosophila melanogaster Orai was crystallized in a hexameric conformation with individual dimers stabilized through antiparallel CC interactions between the cytosolic C-terminal helices 25. Remarkably, the antiparallel configuration of the Orai C-terminal helices in D. melanogaster appear primed for an interaction with STIM, highly analogous to the one elucidated in our human STIM1 CC1[TM-distal]-CC2:Orai1 C272-292 complex structure (Fig. 4a). The interhelix angle between the two interacting D. melanogaster Orai C-terminal helices (i.e. 152°) is very similar to the angle observed in our human complex structure (i.e. 136°) (Fig. 4a). Docking of three dimer structures of CC1[TM-distal]-CC2:Orai1 C272-292 onto the Orai hexamer by structurally aligning the common Orai C-terminal regions (Fig. 4b and 4c) confirms the noteworthy structural compatibility. Specifically, the N-termini of CC1[TM-distal]-CC2, indicating the positions of CC1[TM-proximal], are directed away from the cytosolic channel face toward the ER membrane; further, the C-termini of CC1[TM-distal]-CC2, marking the locations of CC3, are adjacent to the C-termini from neighbouring CC1[TM-distal]-CC2 dimers and compatible with homotypic oligomerization of CC1[TM-distal]-CC2 via CC3 interactions into a required functional stoichiometry (Fig. 4b).

Bottom Line: STIM1 mutants disrupting CC1:CC1' interactions attenuate, while variants promoting CC1 stability spontaneously activate Orai1 currents.CC2 mutations cause remarkable variability in Orai1 activation because of a dual function in binding Orai1 and autoinhibiting STIM1 oligomerization via interactions with CC3.We conclude that SOCE is activated through dynamic interplay between STIM1 and Orai1 helices.

View Article: PubMed Central - PubMed

Affiliation: University Health Network and Department of Medical Biophysics, Campbell Family Cancer Research Institute, Ontario Cancer Institute, University of Toronto, Room 4-804, MaRS TMDT, 101 College Street, Toronto, Ontario, Canada M5G 1L7.

ABSTRACT
Orai1 calcium channels in the plasma membrane are activated by stromal interaction molecule-1 (STIM1), an endoplasmic reticulum calcium sensor, to mediate store-operated calcium entry (SOCE). The cytosolic region of STIM1 contains a long putative coiled-coil (CC)1 segment and shorter CC2 and CC3 domains. Here we present solution nuclear magnetic resonance structures of a trypsin-resistant CC1-CC2 fragment in the apo and Orai1-bound states. Each CC1-CC2 subunit forms a U-shaped structure that homodimerizes through antiparallel interactions between equivalent α-helices. The CC2:CC2' helix pair clamps two identical acidic Orai1 C-terminal helices at opposite ends of a hydrophobic/basic STIM-Orai association pocket. STIM1 mutants disrupting CC1:CC1' interactions attenuate, while variants promoting CC1 stability spontaneously activate Orai1 currents. CC2 mutations cause remarkable variability in Orai1 activation because of a dual function in binding Orai1 and autoinhibiting STIM1 oligomerization via interactions with CC3. We conclude that SOCE is activated through dynamic interplay between STIM1 and Orai1 helices.

Show MeSH