Molecular Neuroscience and Biophysics (Andrew Plested)

Research

Glutamate Receptors 

Nerve cells in the brain communicate by releasing neurotransmitters, chemicals such as glutamate. The electrical firing of one cell leads to a tiny amount of glutamate being released in a brief pulse. This glutamate is picked up by sensors, called receptors, embedded in the membrane walls of neighbouring cells. Generally, these receptors respond by briefly changing their shape, and opening a tiny pore in the membrane.  Electrical current flows through this pore into the receiving cell. This electrical current can excite the cell to fire its own nerve impulses, passing on the signal. Nerve cells can fire rapidly, often tens or hundreds of times in a second, and so, in order to pass the message reliably, some receptors must work even faster. They receive the glutamate signal, activate and then release the glutamate, ready for another cycle, in a fraction of a second. One kind of glutamate receptor that behaves like this turns out to be important for all kinds of brain functions, such as hearing sounds or recalling memories. Other types of glutamate receptor have slow activations (lasting up to a second) and these convey an entirely different message, which can make the target cell increase the strength of the specific connection. This is one way that the brain stores memories. We follow the notion that by understanding the receptors, we can understand the properties of the connections between nerve cells, and thus unravel how the brain processes and stores information. The receptors themselves are also fascinating microscopic machines that, historically, have been full of interesting surprises.

One avenue of research that we have focused on is how different members of the glutamate receptor family, which derive from very similar genes, are tuned to respond to glutamate in such different ways. AMPA and kainate-type glutamate receptors contain a hotspot which controls both their gating and their ability to follow fast signalling in a highly coupled fashion (Carbone and Plested, 2012). This hotspot lies between the binding pocket for glutamate and the gating apparatus of the membrane ion channel. This coupling was rather unexpected at the molecular level, but it makes sense in terms of signalling in the brain. In AMPA receptors, both effects serve to make synaptic transmission more precise at high frequencies. These properties are important at synapses in the auditory pathway, where synapses can signal in the kilohertz range (Taschenberger and von Gersdorff, 2000). There, AMPA receptor subunit composition changes during development - at the onset of hearing, faster AMPA receptors are recruited (Joshi et al, 2004). More recently, we have extended this analysis to complexes of glutamate receptor subunits with auxiliary proteins (Carbone and Plested 2016).

Another technique that we have employed is to directly crosslink subunits, in order to detect receptor gating motions (Das et al, 2010, Lau et al, 2013, Baranovic et al, 2016, Salazar et al, 2017). By crosslinking with either disulphide bonds or engineered metal bridges during receptor gating, we could relate activation states to domain geometry. These techniques is particularly powerful when combined with the high-resolution maps of glutamate receptor structure from X-Ray crystallographic experiments.

In recent years we have become increasingly interested in optical approaches for controlling and measuring receptor activity. We used unnatural amino acids that are sensitive to UV light to crosslink subunits and inactivate the AMPA receptor (Klippenstein et al, 2014). By fusing fluorescent proteins to receptor domains, we could produce a glutamate receptor that reports its activity by FRET (Zachariassen et al, 2016).

References

Baranovic J. et al (2016) Biophysical Journal
Carbone A.L. and Plested A.J.R. (2012), Neuron
Carbone A.L. and Plested A.J.R. (2016), Nature Communications 
Das U., Kumar J., Mayer M.L. and Plested A.J.R. (2010) PNAS
Joshi, I., Shokralla, S., Titis, P., and Wang, L.Y. (2004), JNeurosci
Klippenstein V., Ghisi V., Wietstruk M. and Plested A.J.R. (2014) JNeurosci
Lau A.Y., et al (2013) Neuron                              
Salazar H., Eibl C.E., Chebli M. and Plested A.J.R. (2017) Nature Communications
Taschenberger, H. and Gersdorff, H.V. (2000), JNeurosci
Zachariassen L.G. et al (2016) PNAS 

Leibniz-Forschungsinstitut für Molekulare Pharmakologie im Forschungsverbund Berlin e.V. (FMP)
Campus Berlin-Buch
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