Structure-Based Modeling of Sigma 1 Receptor Interactions with Ligands and Cholesterol and Implications for Its Biological Function

Abstract

The sigma 1 receptor (S1R) is a 223-amino-acid-long transmembrane endoplasmic reticulum (ER) protein. The S1R plays an important role in neuronal health and it is an established therapeutic target for neurodegenerative and neuropsychiatric disorders. Despite its importance in physiology and disease, the biological function of S1R is poorly understood. To gain insight into the biological and signaling functions of S1R, we took advantage of recently reported crystal structures of human and Xenopus S1Rs and performed structural modeling of S1R interactions with ligands and cholesterol in the presence of the membrane. By combining bioinformatics analysis of S1R sequence and structural modelling approaches, we proposed a model that suggests that S1R may exist in two distinct conformations—“dynamic monomer” (DM) and “anchored monomer” (AM). We further propose that equilibrium between AM and DM conformations of S1R is essential for its biological function in cells, with AM conformation facilitating the oligomerization of S1R and DM conformation facilitating deoligomerization. Consistent with experimental evidence, our hypothesis predicts that increased levels of membrane cholesterol and S1R antagonists should promote the oligomeric state of S1R, but S1R agonists and pathogenic mutations should promote its deoligomerization. Obtained results provide mechanistic insights into signaling functions of S1R in cells, and the proposed model may help to explain neuroprotective effects of S1R modulators.

10th European Calcium Society symposium: The Ca2+-signaling toolkit in cell function, health and disease

“…Ilya Bezprozvanny (UT Southwestern Medical Center at Dallas, Dallas, TX, USA) discussed several mechanisms underlying neurodegeneration, thereby highlighting different novel neuroprotective targets. First, increased levels of ER membrane cholesterol promoted Sigma-1 receptor oligomerization and subsequent stabilization of ER-mitochondrial microdomains, thereby exerting neuroprotective effects ( Zhemkov et al, 2021a , b ; Kim and Bezprozvanny, 2023 ). Second, perturbed neuronal autophagy was highlighted as an important factor underlying the neurodegenerative processes in Alzheimer's disease.…”