Mechanistic view on domains mediating STIM1–Orai coupling

Fahrner, Marc; Muik, Martin; Derler, Isabella; Schindl, Rainer; Fritsch, Reinhard; Frischauf, Irene; Romanin, Christoph

doi:10.1111/j.1600-065x.2009.00815.x

Cited by 102 publications

(82 citation statements)

References 96 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previous studies on the mechanics of SOCE have established that colocalization of STIM1 puncta with Orai CRAC channels equates with activation of calcium entry (12,13,26,(30)(31)(32)(33). Furthermore, while there are CRAC channels other than Orai1 to Orai3, such as select members of the TRPC family, activation of TRPC channels first requires colocalization of STIM1 and an Orai channel before the TRPC channel can be recruited and activated (16,17).…”

Section: Yfp-stim1 Biosensor Cell Linementioning

confidence: 99%

Activation of the Endoplasmic Reticulum Calcium Sensor STIM1 and Store-Operated Calcium Entry by Rotavirus Requires NSP4 Viroporin Activity

Hyser

Utama

Crawford

et al. 2013

J Virol

View full text Add to dashboard Cite

Rotavirus nonstructural protein 4 (NSP4) induces dramatic changes in cellular calcium homeostasis. These include increased endoplasmic reticulum (ER) permeability, resulting in decreased ER calcium stores and activation of plasma membrane (PM) calcium influx channels, ultimately causing a 2-to 4-fold elevation in cytoplasmic calcium. Elevated cytoplasmic calcium is absolutely required for virus replication, but the underlying mechanisms responsible for calcium influx remain poorly understood. NSP4 is an ER-localized viroporin, whose activity depletes ER calcium, which ultimately leads to calcium influx. We hypothesized that NSP4-mediated depletion of ER calcium activates store-operated calcium entry (SOCE) through activation of the ER calcium sensor stromal interaction molecule 1 (STIM1). We established and used a stable yellow fluorescent protein-expressing STIM1 cell line (YFP-STIM1) as a biosensor to assess STIM1 activation (puncta formation) by rotavirus infection and NSP4 expression. We found that STIM1 is constitutively active in rotavirus-infected cells and that STIM1 puncta colocalize with the PMlocalized Orai1 SOCE calcium channel. Expression of wild-type NSP4 activated STIM1, resulting in PM calcium influx, but an NSP4 viroporin mutant failed to induce STIM1 activation and did not activate the PM calcium entry pathway. Finally, knockdown of STIM1 significantly reduced rotavirus yield, indicating STIM1 plays a critical role in virus replication. These data demonstrate that while rotavirus may ultimately activate multiple calcium channels in the PM, calcium influx is predicated on NSP4 viroporin-mediated activation of STIM1 in the ER. This is the first report of viroporin-mediated activation of SOCE, reinforcing NSP4 as a robust model to understand dysregulation of calcium homeostasis during virus infections. C alcium (Ca 2ϩ ) is a ubiquitous secondary messenger, and the concentration of intracellular Ca 2ϩ is tightly regulated. As obligate intracellular parasites, viruses subvert host cell pathways to support robust virus replication. Many viruses disrupt host Ca 2ϩ homeostasis in order to establish a cellular environment conducive for virus replication and assembly (1). One well-established hallmark of rotavirus (RV) infection is dramatic changes in cellular Ca 2ϩ homeostasis, including increased permeability of the endoplasmic reticulum (ER), resulting in decreased ER Ca 2ϩ stores and activation of Ca 2ϩ influx channels in the plasma membrane (PM), ultimately resulting in an elevated cytoplasmic Ca 2ϩ concentration ([Ca 2ϩ ]cyto) (2-4). While both ER Ca 2ϩ stores and extracellular Ca 2ϩ contribute to the increased [Ca 2ϩ ]cyto, the extracellular pool is much greater than the ER stores; therefore, Ca 2ϩ influx through the PM likely accounts for the bulk of the increase in [Ca 2ϩ ]cyto in RV-infected cells. Using expression of individual recombinant RV proteins, nonstructural protein 4 (NSP4) was identified as the sole RV protein responsible for the elevation in [Ca 2ϩ ]cyto levels in Sf9 insect...

show abstract

Section: Yfp-stim1 Biosensor Cell Linementioning

confidence: 99%

Activation of the Endoplasmic Reticulum Calcium Sensor STIM1 and Store-Operated Calcium Entry by Rotavirus Requires NSP4 Viroporin Activity

Hyser

Utama

Crawford

et al. 2013

J Virol

View full text Add to dashboard Cite

show abstract

“…Human STIM1 has 685 amino acids and consists of an approximately 22 kDa N-terminal portion (STIM1-N) located in the ER lumen, a single transmembrane segment and an approximately 51 kDa C-terminal portion (STIM1-C) in the cytoplasm (2). The STIM1-N can be further divided into tandem EF-hand and sterile alpha motif domains (16), whereas the STIM1-C encompasses two coiled-coil domains, a Pro/Ser-rich domain and a Lys-rich domain (17). Structural investigation and biochemical evidence revealed that STIM1-N alone was capable of promoting the transition of itself from a monomer to an oligomer upon release of Ca 2þ from the first EF-hand of STIM1-N; this release is thought to be an initiation event for capacitive Ca 2þ entry (16,18).…”

mentioning

confidence: 99%

Structural and mechanistic insights into the activation of Stromal interaction molecule 1 (STIM1)

Yang

Jin²,

Cai³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

191

405

View full text Add to dashboard Cite

Calcium influx through the Ca 2þ release-activated Ca 2þ (CRAC) channel is an essential process in many types of cells. Upon store depletion, the calcium sensor in the endoplasmic reticulum, STIM1, activates Orai1, a CRAC channel in the plasma membrane. We have determined the structures of SOAR from Homo sapiens (hSOAR), which is part of STIM1 and is capable of constitutively activating Orai1, and the entire coiled coil region of STIM1 from Caenorhabditis elegans (ceSTIM1-CCR) in an inactive state. Our studies reveal that the formation of a SOAR dimer is necessary to activate the Orai1 channel. Mutations that disrupt SOAR dimerization or remove the cluster of positive residues abolish STIM1 activation of Orai1. We identified a possible inhibitory helix within the structure of ceSTIM1-CCR that tightly interacts with SOAR. Functional studies suggest that the inhibitory helix may keep the C-terminus of STIM1 in an inactive state. Our data allowed us to propose a model for STIM1 activation.crystal structure | SOAR | store-operated calcium entry | Stromal interaction molecule

show abstract

“…Additionally, recent mutagenesis studies have implicated conserved acidic residues, including E106 and E190 in the first and third predicted transmembrane (TM) segments, and D110, D112, and D114 in the TM1-TM2 linker region of human Orai1 in shaping ion selectivity (7-10). These studies have led to the notion that the TM1 and TM3 segments of Orai1 flank the ion conduction pathway of the CRAC channel with the acidic residues within these segments forming coordinating sites for the conducting ions (9,11).…”

mentioning

confidence: 99%

Structural determinants of ion permeation in CRAC channels

McNally

Yamashita

Engh

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

132

162

View full text Add to dashboard Cite

CRAC channels generate Ca 2؉ signals critical for the activation of immune cells and exhibit an intriguing pore profile distinguished by extremely high Ca 2؉ selectivity, low Cs ؉ permeability, and small unitary conductance. To identify the ion conduction pathway and gain insight into the structural bases of these permeation characteristics, we introduced cysteine residues in the CRAC channel pore subunit, Orai1, and probed their accessibility to various thiolreactive reagents. Our results indicate that the architecture of the ion conduction pathway is characterized by a flexible outer vestibule formed by the TM1-TM2 loop, which leads to a narrow pore flanked by residues of a helical TM1 segment. Residues in TM3, and specifically, E190, a residue considered important for ion selectivity, are not close to the pore. Moreover, the outer vestibule does not significantly contribute to ion selectivity, implying that Ca 2؉ selectivity is conferred mainly by E106. The ion conduction pathway is sufficiently narrow along much of its length to permit stable coordination of Cd 2؉ by several TM1 residues, which likely explains the slow flux of ions within the restrained geometry of the pore. These results provide a structural framework to understand the unique permeation properties of CRAC channels.Orai1 ͉ STIM1 ͉ store-operated channels C a 2ϩ release-activated Ca 2ϩ (CRAC) channels are the principal route of Ca 2ϩ entry in immune cells and orchestrate functions such as gene expression, motility, and the release of inflammatory mediators (1). Mutations in CRAC channels give rise to devastating immunodeficiencies and abnormalities in muscle, skin, and teeth, highlighting their importance for various organ systems (1). The recent discoveries of STIM1 (the ER Ca 2ϩ sensor), and Orai1 (the CRAC channel pore subunit) have provided major breakthroughs to illuminate the molecular basis of CRAC channel function (2). However, while the identification of these proteins has produced rapid progress in our understanding of the cellular events underlying channel activation, the molecular mechanisms of ion selectivity and permeation remain unclear.CRAC channels are distinguished by an extraordinarily high selectivity for Ca 2ϩ over monovalent ions (P Ca /P Na Ͼ 1,000), a very low unitary conductance (Ͻ1 pS), and low permeability to Cs ϩ and larger monovalent cations (3). The structural underpinnings of these characteristics have been the focus of much debate but are largely unknown. As with most ion channels, the pore properties of CRAC channels are likely shaped by the arrangement and chemistry of pore-lining residues. Thus, to understand the basis of the unique permeation properties of CRAC channels, the residues lining the ion transport pathway need to be elucidated.Orai1 bears little sequence homology to other ion channel proteins, and consequently, there are few clues regarding the contribution of the different parts of the molecule for pore formation. Electrophysiological studies indicate that the exquisite Ca 2ϩ selectivity of CRAC...

show abstract

Mechanistic view on domains mediating STIM1–Orai coupling

Cited by 102 publications

References 96 publications

Activation of the Endoplasmic Reticulum Calcium Sensor STIM1 and Store-Operated Calcium Entry by Rotavirus Requires NSP4 Viroporin Activity

Activation of the Endoplasmic Reticulum Calcium Sensor STIM1 and Store-Operated Calcium Entry by Rotavirus Requires NSP4 Viroporin Activity

Structural and mechanistic insights into the activation of Stromal interaction molecule 1 (STIM1)

Structural determinants of ion permeation in CRAC channels

Contact Info

Product

Resources

About