8.A.63 The Sigma Non-opioid Intracellular Receptor (S1R) Family 

The Sigma-1 Receptor (sigmaR1, OPRS1, SRBP, AAC8) functions in lipid transport from the endoplasmic reticulum and is involved in a wide array of cellular functions, posibly through regulation of the biogenesis of lipid microdomains at the plasma membrane. It is also involved in the regulation of different receptors and ion channels like the potassium channel and may modulate neurotransmitter release. It plays a role in calcium signaling together with ANK2 of the ITP3R-dependent calcium efflux in the endoplasmic reticulum. It also plays a role in several other cell functions including proliferation, survival and death. It was originally identified for its ability to bind various psychoactive drugs. It is involved in learning processes, memory and mood alteration (Jbilo et al. 1997; Wang and Duncan 2006). It is a potential target for treatment of retinal disease (Smith et al. 2018).

Crystal structures of the sigma1 receptor are available (Schmidt et al. 2016). These structures reveal a trimeric architecture with a single transmembrane domain in each protomer. The carboxy-terminal domain of the receptor shows an extensive flat, hydrophobic membrane-proximal surface, suggesting an intimate association with the cytosolic surface of the endoplasmic reticulum membrane in cells. This domain includes a cupin-like β-barrel with the ligand-binding site buried at its centre. This large, hydrophobic ligand-binding cavity shows remarkable plasticity in ligand recognition, binding ligands in similar positions despite dissimilar chemical structures. The protein has a short extracellular N terminus with most of the C terminus extending into the cytoplasm (Schmidt et al. 2016). 

The sigma1 receptor shows an allosteric-like effect on the functions of proteins as diverse as the androgen receptor (Thomas et al. 2017) and G protein-coupled receptors (Kim et al. 2012). It also interacts with a wide range of other classes of signaling proteins, receptors, and channels (Kim and Pasternak 2017).

The sigma-1 receptor is expressed in the central nervous system, including the eye, where it mediates the regulation of ion channels.  The sigma-1 receptor agonist (+)-SKF10047 inhibits potassium chloride (KCl)-induced calcium influx, while the antagonist, BD1047, reverses the inhibitory effect of (+)-SKF10047. Whole-cell patch clamp recordings of rat cultured primary RGCs demonstrated that (+)-SKF10047 inhibited calcium currents. Coimmunoprecipitation studies demonstrated an association between L-type calcium channels and the sigma-1 receptors. Thus,  sigma-1 receptor activation can regulate calcium homeostasis and signaling, likely by directly influencing the activity of L-type voltage-gated calcium channels. Regulation of calcium influx by sigma-1 receptor ligands may represent in part the neuroprotective effect of sigma-1 receptors (Tchedre et al. 2008).  Sigma-1 recpetor antagonists have been used to counteract pain (Vela et al. 2015). This receptor plays a role in neurodegenertive diseases (Ruscher and Wieloch 2015) inculding Alzheimer's disease (Jin et al. 2015).



Abdullah, C.S., R. Aishwarya, S. Alam, N.S. Remex, M. Morshed, S. Nitu, S. Miriyala, M. Panchatcharam, B. Hartman, J. King, M. Alfrad Nobel Bhuiyan, J. Traylor, C.G. Kevil, A.W. Orr, and M.S. Bhuiyan. (2021). The molecular role of Sigmar1 in regulating mitochondrial function through mitochondrial localization in cardiomyocytes. Mitochondrion 62: 159-175. [Epub: Ahead of Print]

Hong, W.C., H. Yano, T. Hiranita, F.T. Chin, C.R. McCurdy, T.P. Su, S.G. Amara, and J.L. Katz. (2017). The sigma-1 receptor modulates dopamine transporter conformation and cocaine binding and may thereby potentiate cocaine self-administration in rats. J. Biol. Chem. [Epub: Ahead of Print]

Jbilo, O., H. Vidal, R. Paul, N. De Nys, M. Bensaid, S. Silve, P. Carayon, D. Davi, S. Galiègue, B. Bourrié, J.C. Guillemot, P. Ferrara, G. Loison, J.P. Maffrand, G. Le Fur, and P. Casellas. (1997). Purification and characterization of the human SR 31747A-binding protein. A nuclear membrane protein related to yeast sterol isomerase. J. Biol. Chem. 272: 27107-27115.

Jin, J.L., M. Fang, Y.X. Zhao, and X.Y. Liu. (2015). Roles of sigma-1 receptors in Alzheimer''s disease. Int J Clin Exp Med 8: 4808-4820.

Kim, F.J. and G.W. Pasternak. (2017). Cloning the sigma2 receptor: Wandering 40 years to find an identity. Proc. Natl. Acad. Sci. USA. [Epub: Ahead of Print]

Kim, F.J., J.M. Schrock, C.M. Spino, J.C. Marino, and G.W. Pasternak. (2012). Inhibition of tumor cell growth by Sigma1 ligand mediated translational repression. Biochem. Biophys. Res. Commun. 426: 177-182.

Rodríguez-Muñoz, M., E. Cortés-Montero, J. Garzón-Niño, and P. Sánchez-Blázquez. (2020). The ALS-related σ1R E102Q Mutant Eludes Ligand Control and Exhibits Anomalous Response to Calcium. Int J Mol Sci 21:.

Ruscher, K. and T. Wieloch. (2015). The involvement of the sigma-1 receptor in neurodegeneration and neurorestoration. J Pharmacol Sci 127: 30-35.

Schmidt, H.R., S. Zheng, E. Gurpinar, A. Koehl, A. Manglik, and A.C. Kruse. (2016). Crystal structure of the human σ1 receptor. Nature 532: 527-530.

Smith, S.B., J. Wang, X. Cui, B.A. Mysona, J. Zhao, and K.E. Bollinger. (2018). Sigma 1 receptor: A novel therapeutic target in retinal disease. Prog Retin Eye Res. [Epub: Ahead of Print]

Tchedre, K.T., R.Q. Huang, A. Dibas, R.R. Krishnamoorthy, G.H. Dillon, and T. Yorio. (2008). Sigma-1 receptor regulation of voltage-gated calcium channels involves a direct interaction. Invest Ophthalmol Vis Sci 49: 4993-5002.

Thomas, J.D., C.G. Longen, H.M. Oyer, N. Chen, C.M. Maher, J.M. Salvino, B. Kania, K.N. Anderson, W.F. Ostrander, K.E. Knudsen, and F.J. Kim. (2017). Sigma1 Targeting to Suppress Aberrant Androgen Receptor Signaling in Prostate Cancer. Cancer Res 77: 2439-2452.

Vela, J.M., M. Merlos, and C. Almansa. (2015). Investigational sigma-1 receptor antagonists for the treatment of pain. Expert Opin Investig Drugs 24: 883-896.

Wang, L. and G. Duncan. (2006). Silencing of sigma-1 receptor induces cell death in human lens cells. Exp Cell Res 312: 1439-1446.

Wu, N.H., Y. Ye, B.B. Wan, Y.D. Yu, C. Liu, and Q.J. Chen. (2021). Emerging Benefits: Pathophysiological Functions and Target Drugs of the Sigma-1 Receptor in Neurodegenerative Diseases. Mol Neurobiol 58: 5649-5666.

Zhang, K., Z. Zhao, L. Lan, X. Wei, L. Wang, X. Liu, H. Yan, and J. Zheng. (2017). Sigma-1 Receptor Plays a Negative Modulation on N-type Calcium Channel. Front Pharmacol 8: 302.


TC#NameOrganismal TypeExample

Sigma-1 non-opioid intracellular receptor SGMR-1, OPRS1, SRBP, AAG8) of 223 aas and 2 or 3 TMSs.  It influences the activities of various channels and carriers including L-type Ca2+ channels (Tchedre et al. 2008) and the dopamine transporter, DAT (2.A.22.1.3; Hong et al. 2017). Sigma-1 receptors play a negative modulation role on N-type Ca2+ channels involving chaperone-mediated direct interactions (Zhang et al. 2017). The sigma-1 receptor is a theraputic target in retinal disease (Smith et al. 2018). The sigma1R E102Q mutant exhibits an anomalous response to cytosolic calcium levels, altered affinity for target proteins, and a loss of response to regulatory ligands, and these modifications may contribute to the onset of juvenile ALS (Rodríguez-Muñoz et al. 2020). Sigmar1 localizes to mitochondrial membranes and is indispensable for maintaining mitochondrial respiratory homeostasis in cardiomyocytes (Abdullah et al. 2021). It helps to locate endoplasmic reticulum calcium channels, regulates calcium homeostasis, and acts as a molecular chaperone to control cell fate and participate in signal transduction. It plays a role in protecting neurons through a variety of signaling pathways and participates in the regulation of cognition and motor behavior closely related to neurodegenerative diseases. Sig-1R is a target for alleviating Alzheimer's disease and other neurodegenerative diseases (Wu et al. 2021).

Sigma-1 receptor of Homo sapiens


The ERG2 and sigma1 receptor-like protein of 194 aas and 2 TMSs

Sigma-1 recpeptor of Trichosporon oleaginosus


C-8 sterol isomerase of 217 aas and 3 TMSs.

isomerase of Candida dubliniensis


Uncharacterized protein of 374 aas and 2 - 3 TMSs.

UP of Vitis vinifera (Grape)


Uncharacterized protein of 228 aas and 3 mildly hydrophobic peaks.

UP of Caenorhabditis elegans


C8 sterol isomerase of 191 aas and 1 - 3 putative TMSs.

Isomerase of Mycobacterium gilvum