Megakines - novel tools for structural insight into receptor:chemokine complexes

Chemokines are small, secreted cytokines that activate membrane receptors belonging to the G protein-coupled receptor (GPCR) superfamily.The chemokine-receptor interactions control crucial physiological processes, but are also implicated in many pathologies, including atherosclerosis, inflammatory diseases, HIV infection or cancer, and hold a great potential for therapeutic intervention.Yet, although GPCRs are the target of about one third of currently marketed drugs, only three of them act on chemokine receptors, essentially due to poor structural understanding of the intricate interactions with their ligands. Indeed, about 50 chemokines and 20 receptors have been identifiedin humans. Their interactions require precise orchestration, as a chemokine may bind to several receptors, while a single chemokine receptor has multiple ligands. However, the structural determinants dictating ligand specificity and receptor activation remain elusive.Lately, cryo-EM has emerged as a ground-breaking technique for elucidating molecular structures but despite recent advancements, analysis of small proteins like receptor:chemokine complexes (∼50 kDa) is still challenging. In this project, we propose an innovative approach to increase the chemokine size, without altering its functionality, through a rigid insertion into a bulky scaffold protein. Such enlarged chemokines, calledMegakines, will facilitate structural analysis of chemokine receptors. The proposed Megakine technology has the potential to revolutionize cryo-EM studies ofchemokine receptors and facilitate the therapeutic development.