Biology subjects

Chitsazi, R.

Publications and source records attributed to Chitsazi, R..

4 recordsLinked to original sources

bioRxiv2026

Elevated conformational dynamics makes ACKR3 activation-prone and G protein-incompetent

The atypical receptor ACKR3 works together with the canonical chemokine receptor CXCR4 to drive cell migration along gradients of their shared agonist CXCL12. CXCR4 promotes chemotaxis by activating canonical G protein pathways and recruiting {beta}-arrestins. ACKR3 indirectly regulates CXCR4-mediated chemotaxis by scavenging CXCL12. Unlike canonical chemokine receptors, ACKR3 does not couple to G proteins and instead is 100% biased towards {beta}-arrestins. CXCR4 activation by CXCL12 is exquisitely sensitive to subtle changes in both receptor and ligand. By contrast, ACKR3 is activation-prone: it recruits {beta}-arrestins in response to many ligands and is much less sensitive to mutations, suggesting distinct activation mechanisms compared to CXCR4. To explore the basis of these differences, we compared the dynamics of ACKR3 and CXCR4 complexes with chemokines using molecular dynamic (MD) simulations. Ten-microsecond atomistic MD simulations revealed that CXCR4 adopts a stable active state when bound to WT CXCL12 but transitions to an inactive state when in complex with the antagonist variant, [P2G]CXCL12. By comparison, ACKR3 exhibits a variable transmembrane (TM) 6 state distribution and persistently "active" TM7 when complexed with either WT CXCL12 or [P2G]CXCL12, the latter retaining substantial agonistic activity at ACKR3. We further identified ligand-mediated residue interaction networks in the TM core that regulate TM6 and TM7 activation in CXCR4 but are absent or disrupted in ACKR3, resulting in less constrained receptor dynamics. These findings were validated by BRET-based assays with CXCL12 and ACKR3 mutants. Together, the data suggests that the unique conformational dynamics of ACKR3 govern its activation propensity, its ligand promiscuity, and its atypical effector coupling.

pharmacology and toxicology↗

bioRxiv2025

Rules of engagement: determinants of chemokine receptor activation and selectivity by CCL27 and CCL28

The distinct functional roles of chemokines CCL27 and CCL28 in epithelial immunity of skin and mucosal tissues, respectively, are coordinated by their shared receptor, CCR10 and the CCL28-specific receptor, CCR3. In this study, we conducted structure-function studies focused on the N-termini of these two chemokines to identify determinants of receptor activation, internalization and binding specificity. Deletion of two N-terminal residues of CCL27 resulted in a CCR10 antagonist, highlighting the critical roles of these residues in driving receptor pharmacology. Extension with a Phe produced a superagonist by occupying an available subpocket in the receptor binding site. Swapping the N-terminus of CCL28 onto the CCL27 globular domain (NT28-CCL27) also resulted in a superagonist of CCR10, but the opposite swap (NT27-CCL28) showed equivalent or reduced activity compared to WT CCL28, indicating that the CCL28 N-terminus is a stronger driver of CCR10 signaling. The effect of these and other mutations were rationalized by AlphaFold models of the CCR10 complexes. AlphaFold modeling also revealed that the reduced size of the binding pocket, and more basic nature of the N-terminus and extracellular loops of CCR3 compared to CCR10, contribute to its specificity for CCL28 while CCR10 accommodates both ligands. The overall basic nature of CCL28 also contributes to its high affinity for glycosaminoglycans, which is likely important for its retention in mucosal tissues. These data illustrate the modular compositions of these chemokines that has evolved to achieve overlapping but non-redundant functions, and the exploitation of this modular nature to produce engineered chemokines for probing or targeting CCR10 in disease contexts.

pharmacology and toxicology↗

bioRxiv2025

The 4th GPCR Dock: assessment of blind predictions for GPCR-ligand complexes in the era of AlphaFold

The GPCR Dock competitions are a series of community-wide assessments of computational structural modeling and ligand docking for G protein-coupled receptors, a central class of drug targets in the human proteome. The assessments are designed to provide an unbiased overview of progress and to pinpoint areas in need of refinement, thus shaping and directing the development of computational modeling methodologies for GPCRs. In the footsteps of 2008, 2010, and 2013 assessments, the 4th round (GPCR Dock 2021) featured five diverse and challenging prediction targets and coincided with the emergence of AlphaFold, the revolutionary Artificial Intelligence (AI) technology for protein structure prediction from amino acid sequences. This report summarizes the assessment results and challenges in the context of the convergent evolution of computational and experimental structure determination techniques for GPCRs. We demonstrate that thanks to the breakthroughs in AI-powered modeling, the accuracy of modern computational models of GPCR complexes with peptides can not only approach but also exceed that of low-resolution experimental structures. However, our results highlight the unwavering need for high-resolution GPCR structure determination, especially with small molecule chemicals, and for the concurrent application of physics-based and expert-guided modeling methods.

molecular biology↗

bioRxiv2023

A subtle structural modification of a synthetic cannabinoid receptor agonist drastically increases its efficacy at the CB1 receptor

The emergence of synthetic cannabinoid receptor agonists (SCRAs) as illicit psychoactive substances has posed considerable public health risks that include fatalities. Many SCRAs exhibit much higher efficacy and potency, compared with the phytocannabinoid {Delta}9-tetrahydrocannabinol (THC), at the cannabinoid receptor 1 (CB1R), a G protein-coupled receptor involved in modulating neurotransmitter release. In this study, we investigated structure activity relationships (SAR) of aminoalkylindole SCRAs at CB1Rs, focusing on 5F-pentylindoles containing an amide linker attached to different head moieties. Using in vitro bioluminescence resonance energy transfer (BRET) assays, we identified a few of SCRAs exhibiting significantly higher efficacy in engaging the Gi protein and recruiting {beta}-arrestin than the reference CB1R full agonist CP55940. Importantly, adding a methyl group at the head moiety of 5F-MMB-PICA yielded 5F-MDMB-PICA, an agonist exhibiting a large increase in efficacy and potency at the CB1R. This pharmacological observation was supported by a functional assay of the effects of these SCRAs on glutamate field potentials recorded in hippocampal slices. Molecular modeling and simulations of the CB1R bound with either of the SCRAs revealed critical structural determinants contributing to the higher efficacy of 5F-MDMB-PICA, and how these subtle differences propagated to the receptor-G protein interface. Thus, we find that apparently minor structural changes in the head moiety of SCRAs can cause major changes in efficacy. Our results highlight the need for close monitoring of structural modifications of newly emerging SCRAs and their potential for toxic drug responses in humans.

pharmacology and toxicology↗