Distinct regulation of sigma‐1 receptor multimerization by its agonists and antagonists

Abstract

Since its initial proposal four decades ago, extensive studies have shown that the sigma‐1 receptor (σ1R) interacts with and modulates the activity of multiple proteins with important functions. Recent crystal structures of σ1R as a homo‐trimer differ from a dimer‐tetramer model postulated by early work. Further it is not clear whether ligand binding regulates σ1R multimerization. Here I conducted mutational analyses and examined ligands' effects on σ1R oligomerization using novel non‐denaturing gels. In transfected cells σ1R exhibited as monomer, dimer, and mainly as high‐order multimers. Agonists ((+)pentazocine, (+)SKF10,047, DTG, PRE‐084) decreased, whereas antagonists (BD1008, BD1047, BD1063, haloperidol, NE‐100, progesterone) increased σ1R multimers, suggesting that agonists and antagonists differentially affect the stability of σ1R multimers. Mutations at key residues lining the trimerization interface abolished multimerization but preserved dimerization. Intriguingly, deletion of the transmembrane domain (TM) reduced σ1R to monomer. These results demonstrate that multiple domains play crucial roles in coordinating high‐order quaternary organization of σ1R, which may comprise interconvertible oligomeric states in a dynamic equilibrium. σ1R multimers exhibited high‐affinity and high‐capacity [3H](+)pentazocine binding, whereas monomers lacked binding. In competition binding the antagonist haloperidol appeared to show an apparent 10‐fold higher potency in wild‐type σ1R than in mutants with only dimers, which might explain why haloperidol binding increased σ1R multimers. Further, a σ1R mutant (E102Q) implicated in early‐onset amyotrophic lateral sclerosis exhibited as dimer only, suggesting that dysregulation of σ1R quaternary structure impairs its physiological function. Further exploration of ligand‐regulated σ1R multimerization may provide novel approaches to modulate the function of σ1R and its interacting proteins.Support or Funding InformationButler University Faculty Startup FundThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.