First high-resolution structure of a GPCR-arrestin complex

17-06-2020

An international team of scientists led by Chris Tate's group at the MRC Laboratory of Molecular Biology (UK), have solved the first high-resolution structure of arrestin coupled to a non-sensory GPCR, using cryoEM and the MASSIF-1 automated beamline at the ESRF. The β1-adrenoceptor (β1AR) is a GPCR activated by the hormone noradrenaline.

  • Share

G protein-coupled receptors (GPCRs) are integral membrane proteins that transduce chemical signals from the extracellular matrix into the cell. There are ~800 GPCRs encoded by the human genome and they respond to a diverse array of stimuli such as hormones, neurotransmitters, ions, photons and odorants. GPCRs are vital for a cell to survive and their disfunction has been implicated in neurodegeneration, cardiovascular diseases and cancer, and been shown to contribute to obesity, diabetes and mental disorders. This makes them a popular target for drugs.

GPCRs trigger critical intracellular signalling cascades through coupling with either G proteins or arrestins – a process that is called ‘biased agonism’. A receptor can activate more than one signalling cascade and the one which is activated is determined by what activates it (in this case, either the G protein or the arrestin). Certain ligands/drugs can bias this critical signalling towards either G proteins or arrestins.

Published in Nature, the key advance of the study is the comparison of a GPCR with the same ligand (formoterol), coupled to either arrestin or a G protein mimetic at high enough resolution to observe subtle changes in the receptor. Knowledge of these minute differences are critical in understanding biased agonism and, eventually, in being able to control this process

The team of scientists used cryo-EM to determine the structure of the receptor-arrestin complex. However, they also needed the structure of the receptor alone bound to formoterol to allow comparisons with other receptor complexes. The receptor alone is too small for cryo-EM studies so X-ray crystallography, carried out at the the ESRF’s unique fully automated beamline MASSIF-1, was used GPCRs are flexible molecules and crystals tend to vary enormously in their quality. This means that a large number need to be screened to find the few that provide good data. The full automation of sample mounting and data collection on MASSIF-1 allowed a huge number of crystals to be assessed without human presence. Coupled to automatic workflows that identify the best areas of crystals and calculate optimised data collection strategies, high quality data could be collected for these challenging samples clearly showing the effect of the bound drug.

We have used these crystals to develop new algorithms for intelligent data collection because they were so challenging to work with – it is fantastic to see these method developments now supporting important translational research” says Matthew Bowler (EMBL), scientist co-responsible for the operation of MASSIF-1. “The automated routines on MASSIF-1 have allowed the researchers to determine a high-resolution structure of the receptor while spending more time on the electron microscopy. The combination of these two techniques is extremely powerful” adds Didier Nurizzo (ESRF), scientist co-responsible for the operation of MASSIF-1.

As a proof of concept, this work could be highly significant as many drug companies are trying to develop biased drugs to reduce side effects of current medications. A classic example of this is in pain therapy, where long-term use of opiates leads to chronic constipation, tolerance and addiction.

The work was funded by UKRI MRC, the Wellcome Trust, European Research Council, Department of Biotechnology, Indian Institute of Technology, Kanpur, India, Heptares Therapeutics, Council of Scientific and Industrial Research, India, BBSRC and the European Synchrotron Radiation Facility.

 

Further references:

Molecular basis of β-arrestin coupling to formoterol-bound β1-adrenoceptor. Lee, Y., Warne, T., Nehmé, R., Pandey, S., Dwivedi-Agnihotri, H., Chaturvedi, M., Edwards, PC., García-Nafría, J., Leslie, AGW., Shukla, AK., Tate, CG. Nature [Epub ahead of print] Chris’ group page

Top image: β-arrestin (in green) makes extensive contacts with both β1-adrenoceptor (in blue, formoterol in yellow) and the lipid bilayer (in grey) upon coupling. Image credit MRC Laboratory of Molecular Biology.