Block of NMDA receptor channels by endogenous neurosteroids: implications for the agonist induced conformational states of the channel vestibule.

Vojtech Vyklicky,Martin Horak,Hana Chodounska,Marian Novotny,Martin Zapotocky,Petr Kacer,Milos Petrovic,Miloslav Korinek,Katarina Lichnerova,Jiri Cerny,Barbora Krausova,Tereza Smejkalova,Ladislav Vyklicky,Martina Kaniakova,Ales Balik

doi:10.1038/srep10935

Abstract

N-methyl-D-aspartate receptors (NMDARs) mediate synaptic plasticity, and their dysfunction is implicated in multiple brain disorders. NMDARs can be allosterically modulated by numerous compounds, including endogenous neurosteroid pregnanolone sulfate. Here, we identify the molecular basis of the use-dependent and voltage-independent inhibitory effect of neurosteroids on NMDAR responses. The site of action is located at the extracellular vestibule of the receptor’s ion channel pore and is accessible after receptor activation. Mutations in the extracellular vestibule in the SYTANLAAF motif disrupt the inhibitory effect of negatively charged steroids. In contrast, positively charged steroids inhibit mutated NMDAR responses in a voltage-dependent manner. These results, in combination with molecular modeling, characterize structure details of the open configuration of the NMDAR channel. Our results provide a unique opportunity for the development of new therapeutic neurosteroid-based ligands to treat diseases associated with dysfunction of the glutamate system.

Highlights

Among the powerful allosteric modulators of N-methyl-D-aspartate receptors (NMDARs) are neurosteroids that have been shown to induce potentiation, inhibition or mixed effects[5]
Responses mediated by GluN1(T648A)/GluN2B receptors are blocked in a voltage-dependent manner (Fig. 3), indicating that the extracellular vestibule opens to a diameter that allows pregnan-20-on 3α -yl-[(2-trimethylammonio)-e thanoate] (PA-A) to move to the central pore cavity and block the ion flow
The model with the vestibule open wide enough to allow PA-A to move from the extracellular site to the ion channel cavity was considered to mimic the open state of the NMDAR (Fig. 5a–e)

Summary

Introduction

Among the powerful allosteric modulators of NMDARs are neurosteroids that have been shown to induce potentiation, inhibition or mixed effects[5]. These steroids represent a broad class of endogenous compounds whose site of synthesis and action is in the nervous system itself. They play multiple biological roles both during embryogenesis and in adults[6]. The access of PA-S to its site of action is conditioned by the activation of NMDARs by agonists (use-dependent allosteric inhibition). The model of the NMDAR channel opening provides an explanation for the different contributions of GluN1 and GluN2B subunits to the inhibition by the steroid

Methods

Results

Conclusion