CryoEM structure of cannabinoid receptor CB2 with a biased ligands

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G protein-coupled receptors (GPCRs) are transmit signals between the cellular environment and its interior. Due to their key role in cellular signalling, they are the target of a third of marketed drugs. Binding of ligands with agonist activity stabilises particular conformations of a GPCR, which result in the activation of G proteins and arrestin-mediated signalling pathways. It is now widely recognized that "biased" therapeutics, which activate only a subset of specific signalling pathways, offer significant advancement over existing drugs with full agonist or antagonist activity due to higher specificity of action and lower side effects. Significant efforts are now being directed to develop such drugs. However, due to the promiscuity of the GPCRs and complexity of the signalling pathways, it is often difficult to attribute the observed effects of candidate biased ligands to one particular mode of signalling. Cannabinoid receptor CB2 is a valuable drug target for treating inflammatory diseases, pain, osteoporosis, atherosclerosis and brain tumours. We recently identified several CB2 ligands that show strong biased signalling profile. Complementary mutagenesis results suggested that the ligand binding site contains "hot-spots" that mediate signalling induced by the ligand binding, and are likely to affect biased signalling. Our main hypothesise is that CB2 ligands exert their action and signalling bias via specific interactions in the ligand binding pocket. To test this hypothesis, we need structural information of how biased ligands bind the receptor. The project will focus on obtaining a CryoEM structure of CB2 receptor in complex with several biased ligands using CryoEM. The student will learn mammalian cell culture, membrane protein biochemistry and single-particle CryoEM techniques. These skills will be complemented with training pharmacological assays to characterise pharmacology of novel ligands inspired by the structural data. The results of the project will establish a link between the structural changes induced in receptors to their signalling properties and would promote the development of the next generation of "biased" therapeutics.The student will be embedded in the Centre of Membrane Proteins and Receptors (COMPARE), a unique collaboration between the Universities of Birmingham and Nottingham, a centre of GPCR excellence in Europe and worldwide. It offers a vibrant community of over 40 PhD students and post-docs to develop research and presentation skills and an academic network. Additionally, they will work at RCH on CryoEM structure determination and further expanding their academic network.