Key advances have been made on the following topics:
- NMDAR structural dynamics and allosteric mechanisms
NMDARs form large heterotetrameric molecular complexes. A distinguishing feature of NMDARs is their high conformational mobility which underlies their remarkable allosteric potential. Understanding the functional coupling of the various domains remains a major challenge. Using a combination of experimental approaches and in silico analysis, we identified a rotation motion at the interface between the two constitute dimers as a key structural mechanism in GluN2B NMDAR allostery. Surprisingly, we found that in GluN2A receptors, long-range allosteric coupling proceeds through a distinct interface, within local LBD dimers. These results provide the first integrated views of long-distance domains coupling in full-length NMDARs, and highlight the potential of subunit-subunit interfaces as novel sites for pharmacological manipulation of glutamate receptors.
- Molecular optogenetics and NMDAR functional diversity
Reprogramming receptor to artificially respond to light has strong potential for molecular studies and interrogation of biological functions. In the last years, we have designed a set of light controllable NMDARs using either photosensitive amino acids or ligands. In a first work, we provided the first demonstration of real-time detection of molecular rearrangements due to reversible light-switching of single amino acid side-chains inserted into a neuronal receptor. In a second and still ongoing work, we developed a photoswitchable allosteric potentiator for GluN2B-receptors exploiting the GluN2B-selective polyamine modulatory site. We have now obtained full experimental validation of this receptor tool both in vitro, ex vivo and in vivo. Ongoing experiments are currently performed to decipher the specific roles of GluN2B receptors in synapse function and behavior.
- A new family of glycine excitatory NMDA receptors
Based on the discovery of a pharmacological agent (CGP-78608) that uniquely and massively potentiates GluN1/GluN3 receptors (by preventing their desensitization), we discovered that GluN1/GluN3A receptors form glutamate-insensitive NMDARs expressed at high levels in specific brain regions, where they constitute a new type of neuronal receptors gated by glycine. These results have profound implication on our understanding of NMDAR signaling diversity and open new vistas on the roles of glycine in neurotransmission.
- The microenvironment at excitatory synapses
A striking feature of NMDARs is that they can be regulated by their microenvironment in a localized and subunit-specific manner. Tight receptor regulation is critical for normal brain physiology. We focused on NMDAR modulation by two atypical ligands, D-serine and zinc. Using an original ZnT3-Cre mouse line, we are currently mapping the distribution of zincergic neurons and pathways throughout the brain. We also discovered that vesicular zinc is not limited to excitatory synapses but is also accumulated by a specific subpopulation of interneurons in the cortex and hippocampus. Using an original inducible knock-in mouse line that harbor glycine-impaired NMDARs, we unveiled striking effects on synaptic plasticity pointing to major differences in the availability and role of glycine and D-serine as NMDAR co-agonists and synapse regulators.
