Biology subjects

Hartley, O.

Publications and source records attributed to Hartley, O..

3 recordsLinked to original sources

bioRxiv2024

Noncanonical roles of chemokine regions in CCR9 activation revealed by structural modeling and mutational mapping

The G protein-coupled CC chemokine receptor 9 (CCR9) plays a major role in inflammatory bowel disease and has been implicated in cancer. Despite its importance as a drug target, there is limited mechanistic understanding of how CCR9 engages and is activated by its endogenous chemokine agonist CCL25. Here, by combining structural modeling with multimodal pharmacological assessment of receptor mutants, we generated a functional map of the CCR9-CCL25 interaction interface and delineated key determinants of binding, agonism, constitutive activity, and G protein vs arrestin signaling. In contrast to all complexes studied to date, where chemokines drive receptor activation through their N-termini, we determined that CCL25 activates CCR9 via a distinct region, its 30s loop. In support of this non-canonical mechanism, CCR9 signaling is tolerant to alanine mutations in the N-terminus of CCL25 but strongly affected by modifications to the 30s loop. Through molecular evolution of the CCL25 N-terminus, we identified chemokine analogs with enhanced binding properties. However, in contrast to other receptor-chemokine systems, these analogs remained full agonists, consistent with the localization of CCL25 signaling determinants outside of the N-terminus. The non-canonical signature of CCR9 activation provides new insights to aid CCR9 drug discovery and may also inform structure-based design of drugs targeting other chemokine receptors.

molecular biology↗

bioRxiv2020

Structural basis of the activation of the CC chemokine receptor 5 by a chemokine agonist

The human CC chemokine receptor 5 (CCR5) is a G protein-coupled receptor (GPCR) that plays a major role in inflammation and is involved in the pathology of cancer, HIV, and COVID-19. Despite its significance as a drug target, the activation mechanism of CCR5, i.e. how chemokine agonists transduce the activation signal through the receptor, is yet unknown. Here, we report the cryo-EM structure of wild-type CCR5 in an active conformation bound to the chemokine super-agonist [6P4]CCL5 and the heterotrimeric Gi protein. The structure provides the rationale for the sequence-activity relation of agonist and antagonist chemokines. The N-terminus of agonist chemokines pushes onto an aromatic connector that transmits activation to the canonical GPCR microswitch network. This activation mechanism differs significantly from other CC chemokine receptors that bind shorter chemokines in a shallow binding mode and have unique sequence signatures and a specialized activation mechanism. One-sentence summaryThe structure of CCR5 in complex with the chemokine agonist [6P4]CCL5 and the heterotrimeric Gi protein reveals its activation mechanism

biophysics↗

bioRxiv2019

High-Affinity Binding of Chemokine Analogs that Display Ligand Bias at the HIV-1 Co-receptor CCR5

The chemokine receptor CCR5 is a drug target to prevent transmission of HIV/AIDS. We studied four analogs of the native chemokine RANTES (CCL5) that have anti-HIV potencies of around 25 pM, which is more than four orders-of-magnitude higher than that of RANTES itself. It has been hypothesized that the ultra-high potency of the analogs is due to their ability to bind populations of receptors not accessible to native chemokines. To test this hypothesis, we developed a homogeneous dual-color fluorescence cross-correlation spectroscopy (FCCS) assay for saturation and competition binding experiments. The FCCS assay has the advantage that it does not rely on competition with radioactively labeled native chemokines used in conventional assays. We prepared site-specifically labeled fluorescent analogs using native chemical ligation of synthetic peptides, followed by bioorthogonal fluorescent labeling. We engineered a mammalian cell expression construct to provide fluorescently labeled CCR5, which was purified using a tandem immunoaffinity and size-exclusion chromatography approach to obtain monomeric fluorescent CCR5 in detergent solution. We found subnanomolar binding affinities for the two analogs 5P12-RANTES and 5P14-RANTES, and about twenty-fold reduced affinities for PSC-RANTES and 6P4-RANTES. Using homologous and heterologous competition experiments with unlabeled chemokine analogs, we conclude that the analogs all bind at the same binding site; whereas, the native chemokines (RANTES and MIP1) fail to displace bound fluorescent analogs even at tens of micromolar concentrations. Our results can be rationalized with de novo structural models of the N-terminal tails of the synthetic chemokines that adopt a different binding mode as compared to the parent compound.

biophysics↗