Molecular and cellular biophysics of synapses
(1) The subunit assembly mechanism and architecture of the ionotropic glutamate receptors.
Ionotropic glutamate receptors (iGluRs) are ligand-gated ion channel that are critical for excitatory neurotransmission. They are divided into three subtypes (AMPA, NMDA and kainite receptors) based on their pharmacological characteristics. The heteroterameric AMPA receptors play pivotal roles in synaptic plasticity. Their dysfunction is related to a variety of psychiatric and neurological disorders, including schizophrenia, Alzheimera??s disease, ALS, X-linked mental retardation, limbic encephalitis, CNS lupus, and Rasmussena??s encephalitis.
The exact function and trafficking of these receptors depends critically on their subunit composition and organization. However, because of the limited structural information available on native full-length AMPA receptors, the molecular basis for the function, trafficking, and biogenesis of AMPA receptors remains poorly understood. We study the subunit assembly mechanism and the structures of fully assembled AMPA receptors as well as their assembly intermediates.
Our ultimate goal is to identify the structural basis for the function and modulation of AMPA receptors. By investigating recombinant AMPA receptors and genetic variants, we aim to extend our previous electron microscopy studies of brain-derived AMPA receptors. Our research further extends into understanding the molecular assembly and function of NMDA receptors. The precise knowledge of the molecular mechanism of ionotropic glutamate receptor function will pave the path toward developing new drugs for treating a variety of neurological and psychiatric disorders.
(2) AMPA and kainite receptor interactomes facilitate identifying novel functional repertoire of iGluRs
The iGluRs are protein complexes formed of tetrameric assembly of core receptor subunits and auxiliary transmembrane subunits. In the case of AMPA-Rs the auxiliary (and candidate auxiliary) subunits include, stargazin/TARPs, SOL-1, cornichon, CKAMP44/Shisa-9, and synDIG1. Each auxiliary subunit modulates channel trafficking and gating is specific ways. The functional variety of AMPA-Rs is therefore amplified by combinatorial effect caused by different types of AMPA-Rs binding to distinct auxiliary subunits.
The magnitude of molecular variety of iGluR auxiliary (or candidate auxiliary) subunit remains elusive. To gain insight into this question, we have recently conducted a comparative interactome analyses of AMPA and kainite receptors purified from rat brain (Shanks, Savas, Maruo et al. 2012, Cell Reports). With the aid of this large-scale data we were able to identify many candidate auxiliary subunits and/or potential binding partners of AMPA-R and kainite receptors. Among those candidates we have verified GSG1L as novel AMPA-R auxiliary subunit, based on experimental verification by combining methods in biochemistry, electrophysiology and cell biology. In-depth analyses of the biology revolving around GSG1L and further investigation of other potential iGluR interacting membrane proteins identified in our comparative interactome data may reveal novel physiological functions of AMPA-Rs.
(3) Isolation of novel macromolecular complexes from the neuronal membrane.
We believe that there are still novel macromolecules in the membrane that play fundamentally important biological function. Using our strength in membrane biochemistry, we develop new biochemical procedures to isolate new macromolecules from the neuronal membrane. Our interest is not only limited to prototypical transmembrane proteins but also to other molecular entities such as lipid clusters, glycolipid complex, and RNAs. This high-risk high-reward project is partly funded by the NIH EUREKA (Exceptional and Unconventional Research Enabling Knowledge Acceleration) Grant