A refined look at the hidden links of glutamate receptors: Disulfide bonds shape the trafficking and function of NMDA receptors

An international team of researchers from the Department of Neurochemistry of the IEM CAS and the Seoul National University College of Medicine, led by Martin Horák and Professor Young Ho Suh, has uncovered new insights into the function of glutamate NMDA receptors. These receptors play a key role in excitatory signalling in the brain and are critically involved in memory formation by strengthening synaptic connections.

The latest study by first authors Jakub Netolický and Seungha Lee, published in the prestigious Journal of Neuroscience (IF 4.0) (open in a new window), demonstrates that disulfide bonds within the GluN1 subunit profoundly influence not only receptor function but also their trafficking to the cell surface.

The key role of the GluN1 subunit

NMDA receptors (NMDARs) are composed of multiple subunits, among which GluN1 is an essential and ubiquitous component. This study focused specifically on this subunit. Using biochemical approaches in model cell systems, the researchers confirmed the presence of four disulfide bridges – covalent bonds formed between sulfur atoms of cysteine residues.

Targeted disruption of these bonds via mutagenesis led to a marked reduction in cell-surface receptor expression, indicating that disulfide bonds are critical for receptor quality control.

Electrophysiological recordings further revealed that structural alterations in GluN1 also affect receptor function, particularly their sensitivity to the neurotransmitters glutamate and glycine. Some mutated variants showed an increased likelihood of ion channel opening, leading to enhanced signal transmission.

Experiments in primary hippocampal neurons and model cell lines confirmed that disruption of disulfide bonds negatively impacts the early stages of NMDARs trafficking from the endoplasmic reticulum to the cell surface. This process was monitored using the ARIAD system, which enables precise temporal control of receptor release from the endoplasmic reticulum.

A pathogenic variant and its consequences

The study also provides an in-depth characterisation of the pathogenic GluN1-C744Y variant. This mutation reduced surface expression of the receptors while simultaneously increasing their sensitivity to glutamate and glycine.

In primary hippocampal neurons, this imbalance resulted in increased cellular damage due to excessive calcium influx – an effect known as excitotoxicity.

Importantly, the researchers demonstrated that memantine, an NMDARs antagonist approved by the U.S. Food and Drug Administration, inhibits NMDARs carrying this pathogenic variant more effectively than physiological receptors. This finding points to a potential therapeutic benefit for patients harbouring this mutation.

Why is it important?

This study provides new insights into the role of disulfide bonds in regulating both the function and trafficking of NMDAs, including the impact of the pathogenic GluN1-C744Y variant. It shows that even minor changes in the structure of receptors can significantly affect their presence on the cell surface and their function in synaptic transmission.

These findings deepen our understanding of the molecular basis of neurological disorders and suggest new therapeutic opportunities, such as the more targeted use of existing drugs – such as memantine. Ultimately, the study opens the door to more precise personalised treatment strategies, where even fine molecular details may determine therapeutic choice and efficacy.