Data Availability StatementAll relevant data are within the manuscript. when T3 is neutral at pH < 7.3. After deprotonation of T3 (but no additional deprotonation of PS) at pH 7.3, T3 loses potency more slowly with increasing pH than PS. We interpret this total result as indicating the negative charge is not required for inhibition but does increase activity. Finally, Cefuroxime sodium we show that both T3 and PS affect nAChR channel desensitization, which may implicate a binding site homologous to one that was recently indicated for accelerated desensitization of the GABAA receptor by PS. Introduction The nicotinic acetylcholine receptor (nAChR) is an excitatory receptor protein localized in the central nervous system [1], the peripheral nervous system and neuromuscular junction (reviewed in [2]). Pathologies of the receptor, including epilepsy [3] and myasthenia gravis (in muscle-type nAChRs) [4, 5], demonstrate its crucial function in fast synaptic transmission. In muscle-type nAChRs, it is a cation-conducting member of the pentameric ligand-gated ion channel (pLGIC), or Cys-loop receptor superfamily [6C10]. Of the five homologous subunits that comprise the nAChR structure and central pore, two are identical (, , , , ). When acetylcholine molecules bind to the - and - subunit interfaces in the receptors extracellular domain (ECD), conformational changes propagate to its transmembrane domain (TMD). Four alpha helices (M1-M4) from each subunit form the TMD, with the M2 helices from each subunit lining the receptors central pore. Upon binding acetylcholine, the central pores inner diameter increases, permitting ion flux through the channel [11]. The pLGIC superfamily includes glycine receptors, 5-HT3 receptors, and -aminobutyric acid (GABAA) receptors [6], as well as a range of homologs in invertebrates, plants, and prokaryotes [12]. Neurosteroids, either those synthesized in endocrine glands and metabolized, or those synthesized in brain tissue, can have hypnotic [13], anxiolytic [14], anxiogenic [15], anti-convulsant [16], and analgesic effects (for review see [17]), and can have synergistic effects with anesthetics [18, 19]. Previous investigations of pLGICs elucidated structure-function relationships of neurosteroids molecular features [20C23]. The distinction between molecular features of otherwise similar compounds provides insight into binding sites on the receptor; closely-related molecular species can have differing [22, 24] or opposing [10, 25] effects on their target receptor, and the same neurosteroid can have differing effects on alternative receptor isoforms [26C28]. The neurosteroid 3-hydroxy-5-pregnan-20-one Cefuroxime sodium (allopregnanolone) activates the GABAA receptor [29], as does the related 5-pregnane-3,21-diol-20-one (THDOC) [30C32]. The thyroid hormone L-3,3,5-L-triiodothyronine (T3) (Fig 1A) was originally theorized to have neurosteroid-like effects due Cefuroxime sodium to its similarity to neurosteroids size, shape, and lipophilicity [33]. In particular, the results of computational analysis of the overall volumes and shapes of pregnanolone sulfate (PS) and T3 are compared in Figs ?Figs55 and ?and66 of our previous study [33}. Superpositioning of the two molecules showed that not only the molecular volumes, {but also the shapes,|but the shapes also,} {are nearly identical,|are identical nearly,} and no unmatched functional groups extend from the main axis. Additionally, we have previously published molecular dynamics simulations of single molecules of T3 and allopregnanolone (see S1 Movie and S2 Movie of [29]), illustrating the rigidity of these two molecules in an aqueous solution. The rigidity of the steroid scaffold can be compared Cefuroxime sodium to the rigidity of T3 due to the steric hindrance due to the two Rabbit polyclonal to AMPK gamma1 iodines on the inner aromatic Cefuroxime sodium ring of T3. {Open in a separate window Fig 1 Molecular structure of T3 and PS.|Open in a separate window Fig 1 Molecular structure of PS and T3.}Comparisons of structures of the thyroid hormone T3 (A) and the neurosteroid PS (B). {T3 and neurosteroids share common features including molecular volume and.|Neurosteroids and T3 share common features including molecular volume and.}
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