New molecular blueprint breaks ground for neurological therapies
About the School of Medicine Paper of the Month
The School of Medicine newsletter spotlights a recently published faculty research paper in each issue. The goals are to highlight the great research happening at OHSU and to share this information across departments, institutes and disciplines. The monthly paper summary is selected by Senior Associate Dean for Research Mary Stenzel-Poore, Ph.D., Associate Dean for Clinical Science Eric Orwoll, M.D., and Assistant Dean for Basic Research Mary Heinricher, Ph.D.
August 29, 2014
Our brains are exceptionally busy hubs of activity, with over 100 billion neurons working in concert to sense our surroundings, send messages to our limbs to move, process memories and many, many other activities. Each neuron may be connected to thousands of other neurons, sending signals to each other through neurochemical transmissions.
The most common excitatory neurotransmitter is glutamate, which has many different receptors that are involved with neural development and synaptic plasticity. Glutamate receptor malfunction is associated with a spectrum of neurological diseases and neuropsychiatric disorders including schizophrenia, epilepsy and encephalitis.“The N-methyl-D-aspartate (NMDA) receptor is a member of the glutamate receptor family and is essential for communication between neurons in the CNS,” said Eric Orwoll, M.D., associate dean for clinical science and director of the Oregon Clinical Translational Science Institute. “They are large, complex mobile structures that present a serious experimental challenge to protein chemists.” This month’s featured paper, “NMDA receptor structures reveal subunit arrangement and pore architecture,” published recently in the journal Nature, was chosen by Dr. Orwoll.“
Dr. Gouaux and his laboratory have successfully solved the crystal structure of a frog NMDA Receptor, a major advance in the NMDA field,” said Dr. Orwoll. A news release regarding this influential paper was published by OHSU earlier this summer, and can be found here.
UNKNOWN TO KNOWNPrior to this groundbreaking report, the structure of an intact NMDA receptor was unknown. Biochemical analysis has shown that the NMDA receptor is a heterotetrameric complex usually composed of two glycine binding units (GluN1) and two glutamate binding subunits (GluN2A-D). All NMDA receptors contain an amino-terminal domain, a ligand-binding domain, a transmembrane domain, and finally a cytoplasmic domain. Structures of an isolated amino terminal or an isolated ligand-binding domain have been solved, but the overall arrangement of these domains, and more important, their relationship to each other was unclear. Moreover, no structural information about the transmembrane domain was available.
The team was able to determine the crystal structure of an intact frog GluN1-GluN2B NMDA receptor. The structure included the GluN2B-specific allosteric inhibitor, partial agonists and the ion channel blocker, which provide important information into the mechanism of inhibition, activation and deactivation of the receptor.
INSIGHTSAnalysis of the structure shows that subunits are arranged in a 1-2-1-2 fashion, which demonstrates extensive interactions between the amino-terminal and ligand-binding domains and provides structural insights that were unobtainable through previous isolated biochemical experiments or structural analysis. The transmembrane domain, previously uncharacterized even as an isolated domain, contained a closed-blocked ion channel, a pyramidal central vestibule lined by residues implicated in binding ion channel blockers and magnesium and a roughly twofold symmetric arrangement of ion channel pore loops. The inhibitor, agonist and ion channel blocker structures are also visible in the structure, and provide the first insights into how molecular interactions can lead to inactivation of the receptor.
“This work provides a molecular blueprint for the development of new therapeutic agents and as a structural framework for biophysical mechanisms of action,” said Dr. Gouaux.
Future studies will be able to use this atomic level structure to better understand the mechanisms of allosteric modulation, specifically, and the overall mechanisms of gating and ion channel function more broadly.
Dr. Orwoll praised Dr. Gouaux’s work. “This is not only the first step in a long structural exploration, but this is a groundbreaking and critical step as it allows detailed physiological studies and rational pharmacologic approaches to be developed,” he said.
Congratulations to Lee and the entire Gouaux laboratory on this important work!
CITATIONNMDA receptor structures reveal subunit arrangement and pore architecture
Nature. 2014 Jul 10;511(7508):191-7. doi: 10.1038/nature13548. Epub 2014 Jun 22.
Chia-Hsueh Lee, Wei Lü, Jennifer Carlisle Michel, April Goehring, Juan Du, Xianqiang Song, & Eric Gouaux
MORE PUBLISHED PAPERS• Previous School of Medicine Papers of the Month
• Recent OHSU published papers
Pictured above from left to right: Jennifer Michel, Xianqiang Song, Wei Lu, Chia-Hsueh Lee, Juan Du, Eric Gouaux.