A de novo GRIN1 Variant Associated With Myoclonus and Developmental Delay: From Molecular Mechanism to Rescue Pharmacology.

Xiuhua Bozarth,William Dobyns,Jin Zhang,Ding Liu,Weiting Tang,Nabina Paudyal,Gil Shaulsky,Vasanthi Jayaraman,Yuchen Xu,Scott J Myers,Stephen F Traynelis,Sukhan Kim,Rui Song,Hongjie Yuan,Nidhi K Bhatia,Wenshu Xiangwei

doi:10.3389/fgene.2021.694312

Abstract

N-Methyl-D-aspartate receptors (NMDARs) are highly expressed in brain and play important roles in neurodevelopment and various neuropathologic conditions. Here, we describe a new phenotype in an individual associated with a novel de novo deleterious variant in GRIN1 (c.1595C>A, p.Pro532His). The clinical phenotype is characterized with developmental encephalopathy, striking stimulus-sensitive myoclonus, and frontal lobe and frontal white matter hypoplasia, with no apparent seizures detected. NMDARs that contained the P532H within the glycine-binding domain of GluN1 with either the GluN2A or GluN2B subunits were evaluated for changes in their pharmacological and biophysical properties, which surprisingly revealed only modest changes in glycine potency but a significant decrease in glutamate potency, an increase in sensitivity to endogenous zinc inhibition, a decrease in response to maximally effective concentrations of agonists, a shortened synaptic-like response time course, a decreased channel open probability, and a reduced receptor cell surface expression. Molecule dynamics simulations suggested that the variant can lead to additional interactions across the dimer interface in the agonist-binding domains, resulting in a more open GluN2 agonist-binding domain cleft, which was also confirmed by single-molecule fluorescence resonance energy transfer measurements. Based on the functional deficits identified, several positive modulators were evaluated to explore potential rescue pharmacology.

Highlights

N-Methyl-D-aspartate receptors are ligand-gated ionotropic glutamatergic receptors that mediate excitatory synaptic transmission in the central nervous system and play an important role in brain development
To confirm the results from the molecular dynamics (MD) simulations showing a more open GluN2 glutamate-binding domain cleft in the GluN1-P532H mutant, we investigated the distance across the agonist binding domain (ABD) cleft in the GluN2 subunit using smFRET
We report one patient who presented with early onset severe encephalopathy, and striking stimulus-induced myoclonus due to a de novo pathogenic variant in the GRIN1 gene

Summary

Introduction

N-Methyl-D-aspartate receptors are ligand-gated ionotropic glutamatergic receptors that mediate excitatory synaptic transmission in the central nervous system and play an important role in brain development. NMDARs are a multimeric complex of two GluN1 subunits (encoded by the GRIN1 gene) and two GluN2 subunits (encoded by GRIN2A-D) (Traynelis et al, 2010; Hansen et al, 2021). All NMDAR GluN subunits share a similar architecture that includes an extracellular amino terminal domain (NTD, known as ATD), a bi-lobed extracellular agonist binding domain (ABD), a transmembrane domain (TMD containing M1, M2, M3, and M4), and an intracellular carboxyl terminal domain (CTD). Activation of NMDARs requires both glycine binding to the GluN1 subunit and glutamate binding to the GluN2 subunit. NMDARs play critical roles in normal brain function, such as neural development, synaptic plasticity, learning, memory, and motor function

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Results

Conclusion