Structural and functional analysis of the human chemokine receptor and HIV-1 co-receptor CCR5

This thesis describes the elucidation of the activation mechanism of the human CC chemokine receptor 5 (CCR5) by a chemokine analog, its signaling complexes with the heterotrimeric Gi protein, and subsequent interactions with arrestin2.
Chapter 1 presents a general introduction to G protein-coupled receptor (GPCR) biology and recent advances in the structure elucidation of GPCRs and their signaling complexes. Additionally, the chapter covers the biology of chemokine receptors, focusing on the role of CCR5 in the human immune system.
Chapter 2 describes the cryo-EM structure of wild-type human CCR5 in an active conformation bound to the super-agonist [6P4]CCL5 and the heterotrimeric Gi. The structure of the signaling complex allowed to describe the activation mechanism of CCR5 and to elucidate key elements of the variable pharmacology of CCL5 analogs. These results shed new light on the molecular pharmacology of chemokine receptors and show how a chemokine receptor can be activated by the ‘deep’ binding of the agonist N-terminus into the orthosteric receptor pocket.
Chapter 3 provides a detailed protocol for the biochemical preparation of the [6P4]CCL5•CCR5•Gi signaling complex and describes current advances in chemokine structure determination and associated challenges. An additional NMR characterization of the [5P14]CCL5 partial agonist and [5P12]CCL5 antagonist chemokines is given in the Appendix of this Chapter.
Chapter 4 focuses on the last step of the GPCR signaling cascade – the interaction of CCR5 with arrestin2. Two high-resolution X-ray structures of human arrestin2 in complex with two distinct CCR5 C-terminal phosphopeptides were solved. These structures, in combination with mass spectrometry, NMR, and biochemical and cellular assays, uncovered a key GPCR phosphomotif, which is recognized by arrestin2 and enables its tight association with a GPCR. A further analysis of available structural and functional data on GPCR•arrestin interactions suggests how a certain arrangement of phosphoresidues within the intracellular side of GPCRs define arrestin2 and arrestin3 isoforms specificities.
Chapter 5 describes the isolation of the full-length [6P4]CCL5•CCR5•arrestin2 complex, its biochemical and structural characterization. Furthermore, it discusses the challenges of the structural analysis of this complex.