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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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Related in: MedlinePlus

CC1[TM-distal]-CC2 structural changes associated with Orai1 C272-292 bindinga, V324 and L328’ side chain (green sticks) proximity in the apo α1:α1’ interface. The distance between the V324-Cβ and L328’-Cγ atoms is indicated (broken black line). b, V324 and L328’ side chain (green sticks) proximity in α1:α1’ interface of the CC1[TM-distal]-CC2:Orai1 C272-292 structure. The distance between the V324-Cβ and L328’-Cγ atoms is indicated (red broken line). c, Central pivot point of the apo α2:α2’ interface. The intermolecular Y362-OH (green sticks) distance (broken black line) is shown. d, Central α2:α2’ pivot point in the CC1[TM-distal]-CC2:Orai1 C272-292 structure. The intermolecular Y362-OH (green sticks) distance (broken red line) is shown. The Orai1 L273-Cγ (brown sticks) to Y362-OH and intermolecular Y361-OH (green sticks) distances (broken black lines) are also shown. e, Distance between the α2 helical axes in the apo (blue cartoons; broken black line) versus Orai1 C272-292-bound (white cartoons; broken red line) states. f, Angular opening (broken curved line) of the C-terminal α2 region upon Orai1 C272-292 binding. The apo α2 helices (blue cartoons) are shown relative to Orai1-bound α2 helices (white cartoons). g, Surface electrostatics of the CC1[TM-distal]-CC2 structure. The distinct α1:α1’ acidic and the C-terminal basic residues are labelled. h, Electrostatic complementarity between CC1[TM-distal]-CC2 and Orai1 C272-292 derived from the complex structure. The basic rim residues of the SOAP (broken black circle) and acidic patches are labelled. The Orai1 C272-292 peptides (yellow cartoons) and the acidic side chains are shown (red space fill). The electrostatic gradient in (g) and (h) is from −2 (red) to +2 (blue) kT/e.
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Figure 2: CC1[TM-distal]-CC2 structural changes associated with Orai1 C272-292 bindinga, V324 and L328’ side chain (green sticks) proximity in the apo α1:α1’ interface. The distance between the V324-Cβ and L328’-Cγ atoms is indicated (broken black line). b, V324 and L328’ side chain (green sticks) proximity in α1:α1’ interface of the CC1[TM-distal]-CC2:Orai1 C272-292 structure. The distance between the V324-Cβ and L328’-Cγ atoms is indicated (red broken line). c, Central pivot point of the apo α2:α2’ interface. The intermolecular Y362-OH (green sticks) distance (broken black line) is shown. d, Central α2:α2’ pivot point in the CC1[TM-distal]-CC2:Orai1 C272-292 structure. The intermolecular Y362-OH (green sticks) distance (broken red line) is shown. The Orai1 L273-Cγ (brown sticks) to Y362-OH and intermolecular Y361-OH (green sticks) distances (broken black lines) are also shown. e, Distance between the α2 helical axes in the apo (blue cartoons; broken black line) versus Orai1 C272-292-bound (white cartoons; broken red line) states. f, Angular opening (broken curved line) of the C-terminal α2 region upon Orai1 C272-292 binding. The apo α2 helices (blue cartoons) are shown relative to Orai1-bound α2 helices (white cartoons). g, Surface electrostatics of the CC1[TM-distal]-CC2 structure. The distinct α1:α1’ acidic and the C-terminal basic residues are labelled. h, Electrostatic complementarity between CC1[TM-distal]-CC2 and Orai1 C272-292 derived from the complex structure. The basic rim residues of the SOAP (broken black circle) and acidic patches are labelled. The Orai1 C272-292 peptides (yellow cartoons) and the acidic side chains are shown (red space fill). The electrostatic gradient in (g) and (h) is from −2 (red) to +2 (blue) kT/e.

Mentions: Along with the ‘a’ and ‘d’ interactions, the α1:α1’ interface exhibits central V324:L328’ hydrophobic side chain packing in the absence of Orai1 C272-292 binding (Fig. 2a). In complex with Orai1 C272-292, the α1 helices undergo a registry shift, facilitating closer V324:V324’ side chain interactions. The helix registry shift causes the distance between the V324-Cβ and L328’-Cγ atoms to increase from ~4.6 Å in the apo state to ~8.1 Å in the Orai1 C272-292-bound state (Fig. 2b). Two marked conformational changes occur in the α2:α2’ interface to accommodate the Orai1 C272-292 peptides at opposite ends of the SOAP. First, the α2 helices become separated in the Orai1 C272-292-bound state compared to the apo state. This α2:α2’ dilation is illustrated by the Y362:Y362’ pivot point residues which move from a distance of ~3.2 Å in the apo form (Fig. 2c) to ~11.0 Å in the Orai1 C272-292-bound state (OH groups; Fig. 2d); moreover, the distance between the α2 helical axes increases by ~5.6 Å after this separation (Fig. 2e), and the Y362 side chains interact with L273 of the Orai1 C272-292 peptides (Fig. 2d). Second, the C-terminal half of the α2 helices hinge away from L1’ by ~30.8° at the Y362 pivot point (Fig. 2f). This angular opening of the α2 helices allows supercoiling with Orai1 C272-292 in the SOAP to occur.


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)

CC1[TM-distal]-CC2 structural changes associated with Orai1 C272-292 bindinga, V324 and L328’ side chain (green sticks) proximity in the apo α1:α1’ interface. The distance between the V324-Cβ and L328’-Cγ atoms is indicated (broken black line). b, V324 and L328’ side chain (green sticks) proximity in α1:α1’ interface of the CC1[TM-distal]-CC2:Orai1 C272-292 structure. The distance between the V324-Cβ and L328’-Cγ atoms is indicated (red broken line). c, Central pivot point of the apo α2:α2’ interface. The intermolecular Y362-OH (green sticks) distance (broken black line) is shown. d, Central α2:α2’ pivot point in the CC1[TM-distal]-CC2:Orai1 C272-292 structure. The intermolecular Y362-OH (green sticks) distance (broken red line) is shown. The Orai1 L273-Cγ (brown sticks) to Y362-OH and intermolecular Y361-OH (green sticks) distances (broken black lines) are also shown. e, Distance between the α2 helical axes in the apo (blue cartoons; broken black line) versus Orai1 C272-292-bound (white cartoons; broken red line) states. f, Angular opening (broken curved line) of the C-terminal α2 region upon Orai1 C272-292 binding. The apo α2 helices (blue cartoons) are shown relative to Orai1-bound α2 helices (white cartoons). g, Surface electrostatics of the CC1[TM-distal]-CC2 structure. The distinct α1:α1’ acidic and the C-terminal basic residues are labelled. h, Electrostatic complementarity between CC1[TM-distal]-CC2 and Orai1 C272-292 derived from the complex structure. The basic rim residues of the SOAP (broken black circle) and acidic patches are labelled. The Orai1 C272-292 peptides (yellow cartoons) and the acidic side chains are shown (red space fill). The electrostatic gradient in (g) and (h) is from −2 (red) to +2 (blue) kT/e.
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Related In: Results  -  Collection

Show All Figures
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Figure 2: CC1[TM-distal]-CC2 structural changes associated with Orai1 C272-292 bindinga, V324 and L328’ side chain (green sticks) proximity in the apo α1:α1’ interface. The distance between the V324-Cβ and L328’-Cγ atoms is indicated (broken black line). b, V324 and L328’ side chain (green sticks) proximity in α1:α1’ interface of the CC1[TM-distal]-CC2:Orai1 C272-292 structure. The distance between the V324-Cβ and L328’-Cγ atoms is indicated (red broken line). c, Central pivot point of the apo α2:α2’ interface. The intermolecular Y362-OH (green sticks) distance (broken black line) is shown. d, Central α2:α2’ pivot point in the CC1[TM-distal]-CC2:Orai1 C272-292 structure. The intermolecular Y362-OH (green sticks) distance (broken red line) is shown. The Orai1 L273-Cγ (brown sticks) to Y362-OH and intermolecular Y361-OH (green sticks) distances (broken black lines) are also shown. e, Distance between the α2 helical axes in the apo (blue cartoons; broken black line) versus Orai1 C272-292-bound (white cartoons; broken red line) states. f, Angular opening (broken curved line) of the C-terminal α2 region upon Orai1 C272-292 binding. The apo α2 helices (blue cartoons) are shown relative to Orai1-bound α2 helices (white cartoons). g, Surface electrostatics of the CC1[TM-distal]-CC2 structure. The distinct α1:α1’ acidic and the C-terminal basic residues are labelled. h, Electrostatic complementarity between CC1[TM-distal]-CC2 and Orai1 C272-292 derived from the complex structure. The basic rim residues of the SOAP (broken black circle) and acidic patches are labelled. The Orai1 C272-292 peptides (yellow cartoons) and the acidic side chains are shown (red space fill). The electrostatic gradient in (g) and (h) is from −2 (red) to +2 (blue) kT/e.
Mentions: Along with the ‘a’ and ‘d’ interactions, the α1:α1’ interface exhibits central V324:L328’ hydrophobic side chain packing in the absence of Orai1 C272-292 binding (Fig. 2a). In complex with Orai1 C272-292, the α1 helices undergo a registry shift, facilitating closer V324:V324’ side chain interactions. The helix registry shift causes the distance between the V324-Cβ and L328’-Cγ atoms to increase from ~4.6 Å in the apo state to ~8.1 Å in the Orai1 C272-292-bound state (Fig. 2b). Two marked conformational changes occur in the α2:α2’ interface to accommodate the Orai1 C272-292 peptides at opposite ends of the SOAP. First, the α2 helices become separated in the Orai1 C272-292-bound state compared to the apo state. This α2:α2’ dilation is illustrated by the Y362:Y362’ pivot point residues which move from a distance of ~3.2 Å in the apo form (Fig. 2c) to ~11.0 Å in the Orai1 C272-292-bound state (OH groups; Fig. 2d); moreover, the distance between the α2 helical axes increases by ~5.6 Å after this separation (Fig. 2e), and the Y362 side chains interact with L273 of the Orai1 C272-292 peptides (Fig. 2d). Second, the C-terminal half of the α2 helices hinge away from L1’ by ~30.8° at the Y362 pivot point (Fig. 2f). This angular opening of the α2 helices allows supercoiling with Orai1 C272-292 in the SOAP to occur.

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
Related in: MedlinePlus