Structural biology offers new perspectives for the treatment of psychiatric disorders

Structural biology offers new perspectives for the treatment of psychiatric disorders

Credit: GlyT1 (light blue) is a protein that transports glycine across the cell membrane (gray). To do this, it is opened alternately to the outside and inside of the cell. Unlike other neurotransmitter transporters, it is bound by the inhibitor (orange) from the intracellular side, rather than the extracellular one. The lateral body, a synthetic mini-antibody (dark blue), also inhibits GlyT1 by binding to a new extracellular site. Credit: Azadeh Shahsavar / DANDRITE

Glycine is the smallest amino acid – one of the building blocks of proteins. It also acts as a neurotransmitter in the brain, enabling neurons to communicate with each other and modulate neuronal activity. Many researchers have focused on increasing glycine levels in synapses to find an effective treatment for schizophrenia. This can be done using inhibitors that target Glycine Transporter 1 (GlyT1), a protein that sits in neuronal cell membranes and is responsible for the uptake of glycine into neurons. However, the development of such drugs is hampered because the 3D structure of GlyT1 was not known.

To determine the structure of GlyT1, researchers at the Danish Research Institute of Translational Neuroscience (DANDRITE), which is part of the Nordic EMBL Partnership for Molecular Medicine, F. Hoffmann-La Roche, EMBL Hamburg, University of Zurich, Aarhus University, and Linkster Therapeutics have joined forces. “This project required multidisciplinary collaboration and unique expertise from different laboratories over several years,” says Azadeh Shahsavar, first author of the study and now an assistant professor at DANDRITE. She took the measurements for the study during her time as a postdoc in the EMBL Interdisciplinary Postdocs (EIPOD) program, during which she worked at EMBL Hamburg, DANDRITE and Roche.

Poul Nissen, director of DANDRITE and a senior researcher in the study, says: “We are very grateful to the EMIP’s EIPOD scheme and the Nordic EMBL Partnership for keeping us on track for so long and enabling us to do a lot. “We would not have succeeded without it, and without Azadeh’s perseverance, of course!”

Overcoming challenges in studying Glycine Transporter 1

GlyT1 was particularly challenging to study because it is unstable when extracted from the cell membrane. To stabilize it, scientists have combined several approaches, such as creating more stable variants of the protein. To capture the transporter in a clinically relevant condition, the team used a chemical created by Roche that binds and stabilizes GlyT1 from the inside and designed a synthetic mini-antibody (side body) that binds it from the outside.

The scientists tested 960 different conditions and managed to obtain GlyT1 crystals in one of them. “The crystals were very small and difficult to image. We chose to measure them at EMBL Hamburg’s bar line P14, which is very suitable for challenging experiments like this,” says Azadeh. The X-ray beam at P14 is particularly strong and focused, and its equipment contains features adapted for working with micrometer-sized crystals. However, the quality of the crystals was variable, which made the collection of data challenging. Eventually, Azadeh’s perseverance paid off. “I remember when I first saw the electron density of the inhibitor. I was so excited that I could not sleep for two nights,” she says. “You live for those rewarding moments.”







Credit: 3D Molecular Structure of Glycine Transporter 1. GlyT1 (teal) transports glycine through the cell membrane. Unlike inhibitors of most neurotransmitter transporters, the inhibitor used in this study binds (green) GlyT1 from the intracellular side, rather than the extracellular one. The lateral body, a synthetic mini-antibody (pink), also inhibits GlyT1 by binding to a new extracellular site. Credit: Azadeh Shahsavar / DANDRITE

The last challenge was the data analysis. While the crystals gave only poor refraction patterns due to their small size, the strong X-rays destroyed the crystals in less than a second. A single crystal would only provide partial information about the structure, so Azadeh had to collect data from hundreds of crystals. “The processing of such a large amount of data was possible thanks to the unique infrastructure at EMBL Hamburg,” she says. The combination of partial datasets was complicated for the existing software, but the Schneider group at EMBL Hamburg wrote software designed specifically for such cases. This enabled Azadeh to merge datasets into a complete picture of GlyT1 with a 3.4 Å resolution (1 Å, or ångström, is one ten billionth of a meter – about the size of a typical atom). “I really enjoyed working with people with different scientific backgrounds. Everyone contributed their unique expertise that made this study possible,” says Azadeh.

For Thomas Schneider, Joint Head of Research Infrastructures at EMBL Hamburg, the study is a perfect example that highlights the importance of scientific excellence and the availability of leading infrastructures for advancement in research. “For challenging projects such as these, we like to employ the methodological expertise of our staff and make full use of the technological capabilities of our bar lines and sample preparation facilities. The DESY campus and the versatile high-precision diffractometer that work in collaboration between EMBL Hamburg, EMBL Grenoble and ARINAX were developed, were the key to this project. ‘

Azadeh agrees. “The excellence, infrastructure, hardware and software offered by EMBL is of the highest quality, and it is constantly being improved,” she adds.

Blueprint for new therapy

The analysis revealed an unexpected structure of GlyT1. Unlike other neurotransmitter transporters, which are bound from the outside of the cell membrane by their inhibitors, GlyT1 is bound by the inhibitor from the inside. “The structure was a surprise to us. It appears that the GlyT1 inhibitor must first cross the cell membranes before it can access GlyT1 from the neurons,” said Roger Dawson, a senior author in the study.

“This structure provides a blueprint for the development of new inhibitors of GlyT1, whether it be organic molecules or antibodies,” Roger explains. “The body part developed for this study binds GlyT1 at a previously unknown binding site and includes it in a state in which it can no longer transport glycine. We can use this knowledge to develop drugs that are not just on GlyT1, but also on other membrane transport proteins in the future. ”


Determination of glycine transporter opens new avenues in the development of psychiatric drugs


More information:
Azadeh Shahsavar et al., Structural insights into inhibition of glycine reuptake, Nature (2021). DOI: 10.1038 / s41586-021-03274-z

Provided by the European Molecular Biology Laboratory

Quotation: Structural Biology Opens New Perspectives for the Treatment of Psychiatric Disorders (2021, April 6) Retrieved April 7, 2021 from https://phys.org/news/2021-04-biology-perspectives-psychiatric-disorders.html

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