Structural insights into ligand-recognition, activation, and signaling-bias at the complement C5a receptor, C5aR1

Shukla, A. K.; Saha, S.; Maharana, J.; Yadav, M.; Sarma, P.; Singh, V.; Mohapatra, S.; Soni, C.; Mishra, S.; Ganguly, M.; Chami, M.; Banerjee, R.

doi:10.1101/2023.01.14.524051

bioRxiv · 10.1101/2023.01.14.524051

Structural insights into ligand-recognition, activation, and signaling-bias at the complement C5a receptor, C5aR1

Shukla, A. K.·Saha, S.·Maharana, J.·Yadav, M.·Sarma, P.·Singh, V.·Mohapatra, S.·Soni, C.·Mishra, S.·Ganguly, M.·Chami, M.·Banerjee, R.

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Abstract

Activation of the complement cascade is a critical part of our innate immune response against invading pathogens, and it operates in a concerted fashion with the antibodies and phagocytic cells towards the clearance of pathogens. The complement peptide C5a, generated during the activation of complement cascade, is a potent inflammatory molecule, and increased levels of C5a are implicated in multiple inflammatory disorders including the advanced stages of COVID-19 pathophysiology. The proximal step in C5a-mediated cellular and physiological responses is its interaction with two different seven transmembrane receptors (7TMRs) known as C5aR1 and C5aR2. Despite a large body of functional data on C5a-C5aR1 interaction, direct visualization of their interaction at high-resolution is still lacking, and it represents a significant knowledge gap in our current understanding of complement receptor activation and signaling. Here, we present cryo-EM structures of C5aR1 activated by its natural agonist C5a, and a G-protein-biased synthetic peptide ligand C5apep, in complex with heterotrimeric G-proteins. The C5a-C5aR1 structure reveals the ligand binding interface involving the N-terminus and extracellular loops of the receptor, and we observe that C5a exhibits a significant conformational change upon its interaction with the receptor compared to the basal conformation. On the other hand, the structural details of C5apep-C5aR1 complex provide a molecular basis to rationalize the ability of peptides, designed based on the carboxyl-terminus sequence of C5a, to act as potent agonists of the receptor, and also the mechanism underlying their biased agonism. In addition, these structural snapshots also reveal activation-associated conformational changes in C5aR1 including outward movement of TM6 and a dramatic rotation of helix 8, and the interaction interface for G-protein-coupling. In summary, this study provides previously lacking molecular basis for the complement C5a recognition and activation of C5aR1, and it should facilitate structure-based discovery of novel lead molecules to target C5aR1 in inflammatory disorders.

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Shukla, A. K., Saha, S., Maharana, J., Yadav, M., Sarma, P., Singh, V., Mohapatra, S., Soni, C., Mishra, S., Ganguly, M., Chami, M., Banerjee, R.. 2023-01-17. Structural insights into ligand-recognition, activation, and signaling-bias at the complement C5a receptor, C5aR1. https://doi.org/10.1101/2023.01.14.524051

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