Unlocking the structural secrets of complex protein drug targets

Summary: Understanding how the medicines we discover and develop interact with the proteins they are designed to target is vital. For the best chance of success, we need to ensure they are not only hitting the right target but that they are having the right effect and are considered safe before entering clinical trials.

The field of structure-based drug design – a cornerstone of modern drug discovery – fundamentally depends on technologies that can unlock the 3D structural secrets of complex proteins. Using the revolutionary technology of cryo-electron microscopy (cryo-EM), which earned its inventors the Nobel Prize for Chemistry, our scientists gain vital clues about a protein’s biological function, its role in disease and its potential interactions with our candidate drugs.

CryoEM is able to uncover exquisite detail of target molecules and how drug candidates can bind an interact to help guide novel drug discovery

The electron beams setting the world of structural biology alight

Cryo-EM works by flash-freezing - fast enough to stop the water present forming ice crystals - a microscopic protein sample in a single-molecule-thick layer of vitreous ice. Using electron beams, hundreds of thousands of images of individual molecules within the sample are captured from multiple viewpoints, allowing the computational construction of an exquisitely detailed 3D model. These atomic resolution models even help reveal how structures within the molecules move and change as they perform their functions.

Within AstraZeneca, cryo-EM has already enabled the identification of a number of world-first protein structures all of which are telling us new information about a range of targets and drug candidates we are working on:

• In collaboration with the Medical Research Council’s Laboratory of Molecular Biology (LMB), we have determined the structure of human ataxia telangiectasia mutated (ATM), a key trigger protein in the DNA damage response and a prime therapeutic target in oncology^1,2
• In collaboration with SciLifeLab at Stockholm University and the Karolinska Institutet, we have revealed the structure of the receptor tyrosine kinase RET – relevant in neurodegenerative disease and diabetes – and proposed a model for its activation and targeting³
• A collaboration with University College London has utilised cryo-EM to elucidate the structure of the enzyme phospholipase Cγ1 in complex with a kinase FGFR1, mutations in the former are associated with resistance to certain cancer drugs such as Bruton’s tyrosine kinase (BTK) inhibitors.⁴
• A collaboration with the University of Cambridge to describe a high-resolution cryo-EM structure for the DNA repair enzyme, DNA-PK, and uncover intricate details of its interactions with other proteins involved in DNA repair pathways.⁵

Sharing knowledge and uniting science to drive discovery

The structural biology team within Discovery Sciences, R&D at AstraZeneca has access to two state-of-the-art cryo-electron microscopes through the Cambridge Pharmaceutical Cryo-EM Consortium, a collaboration with the University of Cambridge, the LMB, leading manufacturer Thermo Fisher and four other pharmaceutical companies in the Cambridge area. This Consortium allows us to not only access the very highest-level technology but facilitates our culture of keeping doors and minds open so we can achieve all we want to achieve in pushing the boundaries of science to deliver life-changing medicines. In Sweden, AstraZeneca’s collaboration with SciLifeLab at Stockholm University and the Karolinska Institutet has provided similar benefits.

References

1. Baretic D et al 2017 https://pubmed.ncbi.nlm.nih.gov/28508083/

2. Baretic D et al 2019 https://pubmed.ncbi.nlm.nih.gov/31255703/

3. Bigalke JM et al 2019 https://advances.sciencemag.org/content/5/7/eaau4202/tab-article-info

4. Liu Y et al 2020 https://pubmed.ncbi.nlm.nih.gov/31918402/

5. Chaplin et al 2020 https://www.nature.com/articles/s41594-020-00517-x