N-Methyl-D-aspartate receptors (NMDARs) are a principal subtype of excitatory ligandgated
ion channel with prominent roles in physiology and disease in the mammalian
central nervous system (CNS). Activation of NMDARs requires binding of both
glutamate and glycine. Apart from its co-agonist action, glycine can also prime NMDARs
for subsequent internalization upon binding of both glutamate and glycine. However, the
molecular basis responsible for mediating and regulating glycine priming and NMDAR
endocytosis is largely unknown. In my thesis, I discovered the principle that although
NMDAR gating and priming share a common requirement for glycine binding, the
molecular constraints for gating are distinct from those for priming through two mutations
of the glycine binding site in GluN1 subunit of the NMDAR that, while maintaining
gating of NMDARs, eliminate glycine priming of the receptors. One of the molecular
signatures of glycine priming is recruitment of the endocytic adaptor protein AP-2. I have
characterized the two regions in GluN2 subunits required for enhanced AP-2 association.
This unexpected result suggests binding of glycine initiates a conformational change
transmitted from GluN1 to GluN2 allowing for docking of endocytic machinery.
Furthermore, I have discovered that naturally occurring splice variants of GluN1 subunit,
containing a 21 amino acid sequence in the N-terminus domain (N1) cassette, abrogate
glycine stimulated AP-2 recruitment and glycine-primed NMDAR internalization. These
findings imply that there are distinct populations of native NMDARs in the CNS – those
lacking N1 that show glycine-primed internalization and those containing N1 that are not
primable. Collectively, my thesis work demonstrates a dramatic all-or-none priming effect
with splice variants of NMDARs, a highly unexpected discovery providing novel insight into the molecular mechanisms and physiological role of glycine priming. Ultimately,
elucidating principles and mechanisms of glycine priming lay the foundation for new
types therapeutic approaches for CNS disorders, approaches without the deleterious
consequences of directly blocking NMDARs.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/34027 |
| Date | 12 December 2012 |
| Creators | Han, Lu |
| Contributors | Salter, Michael |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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