“iGluR retreat”, Pittsburgh, PA 2018

The first ionotropic glutamate receptor retreat (iGluRetreat) was held at Cornell University in Ithaca, NY in 2013 and has been subsequently held on a yearly basis, in 2014 at Buffalo, NY; 2015 at Albany, NY; 2016 at Montreal, Canada; 2017 at Yale, CT. The goal of the meeting is to exchange ideas and to promote stimulating discussions amongst researchers from different disciplines; from functional to structural approaches, computational modeling, medicinal chemistry to synaptic physiology. Attendees and speakers include both principal investigators and trainees, and it has grown to include researchers from around the world.

iGluRetreat2017

This year iGluR retreat will be held at University of Pittsburgh, July 31 – August 2.

Invited speakers are:

  •     Ivet Bahar (University of Pittsburgh)
  •     Ian Coombs (University College London)
  •     Yan Dong (University of Pittsburgh)
  •     Hiro Furukawa (Cold Spring Harbor Laboratory)
  •     Alasdair Gibb (University College London)
  •     Albert Lau (Johns Hopkins University)
  •     Linda Nowak (Cornell University)
  •     Pierre Paoletti (École Normale Supérieure)
  •     Lania Rubio (University of Pittsburgh)
  •     Mike Salter (University of Toronto)
  •     Yael Stern-Bach (Hebrew University of Jerusalem)
  •     Sharon Swanger (Virginia Tech)
  •     Weifeng Xu (MIT)

Official retreat website can be found here

 

Ion Permeation Mechanism in Epithelial Calcium Channel TRVP6

trpv6

Based on TRPV6 crystal structures, molecular dynamics simulations predicted binding sites for calcium, barium and gadolinium inside the channel pore. The first TRPV6 crystal structure was solved in our lab in 2015 and published in 2016 in Nature. We succeeded to determine several crystal structures of the channel bound to Ca2+, Ba2+ and Gd3+ and identified ion binding sites in the channel pore as well as in the extracellular vestibule (recruitment sites). Site locations and ion coordination geometry allowed us to make initial assumptions about ion permeation mechanism in TRPV6. It is well known that at low Ca2+ concentrations, the TRPV6-mediated inward current is mainly carried by Na+ ions. An increase in Ca2+ concentration leads to an increase in Ca2+ current but a reduction of Na+ current. We used MD simulations with varying numbers of Ca2+ and Na+ ions to verify experimental observations and to test our structural models.

Briefly, at low Ca2+ concentrations, only a single calcium ion binds at the narrow constriction of the TRPV6 selectivity filter formed by aspartates D541 and allows Na+ permeation. During ion permeation, no water crosses the channel pore narrow constriction. At high Ca2+ concentrations, calcium permeates the pore according to the knock-off mechanism that includes formation of a short-lived transition state with three calcium ions bound near D541. For Ba2+, the transition state lives longer and the knock-off permeation occurs slower. Gd3+ binds at D541 more tightly, blocks the channel and prevents Na+ from permeating the pore.

Check out these cool movies from the paper:

Movie 1. Na+ permeation through TRPV6 channel

Movie 2. Knock-off mechanism of Ca2+ permeation

The work published in Scientific Reports was done in collaboration with Dr. Maria Kurnikova’s lab from Carnegie Mellon University.

Inhibition of AMPARs by epileptic drugs

AMPA-PMP-1-1024x683
Identification of drug binding sites via crystallography

 

Figure 1. Binding sites for epileptic drugs that negatively regulate AMPARs, showing the AMPAR subunit protein in red ribbon, with the densities for PMP (A), GYKI (B), and CP (C) in ball-stick models, with their densities in green mesh.

 

Ionotropic glutamate receptors (iGluRs), and more specifically AMPA-subtype iGluRs (AMPARs), are emerging as therapeutic targets for epilepsy and other neurodegenerative diseases. However, there is only one FDA-approved drug that targets AMPARs (PMP or perampanel). PMP has significant side effects, and because AMPARs are so prevalent throughout the nervous system and excitatory neurotransmission, specific structural information is needed for the development of more efficacious drugs targeting epilepsy. This information has been previously unknown. In order to understand how PMP and similar molecules work, we solved the structure of AMPARs interacting with several drugs, including PMP, that negatively regulate AMPAR function through a noncompetitive allosteric mechanism (Figure 1, above). These structures allowed us to pinpoint and see how these drugs wedge into a binding pocket in the transmembrane region of the receptor to modulate function, preventing the ion channel in the AMPAR from opening. We also used electrophysiology to probe the drug binding sites, and show that this pocket near the top of the transmembrane region is necessary for modulation of AMPAR function by these drugs. We anticipate that this newly-revealed information will serve as an excellent foundation for the development of new therapeutics to better treat epilepsy and other neurodegenerative diseases. For more information, please read the press release from Columbia University Medical Center and our paper in Neuron.