Recombinant Trachypithecus francoisi C-C chemokine receptor type 5 (CCR5)

What is the basic structure and function of Trachypithecus francoisi CCR5?

Trachypithecus francoisi CCR5 is a G protein-coupled receptor belonging to the beta chemokine receptor family, consisting of approximately 352 amino acid residues with a molecular weight of around 40.6 kDa . The protein features a characteristic seven-transmembrane structure with an extracellular N-terminus, three extracellular loops (EL1, EL2, EL3), three intracellular loops (IL1, IL2, IL3), and an intracellular C-terminus, similar to other primate CCR5 proteins . Functionally, it serves as a receptor for specific chemokines including MCP-2, MIP-1 alpha, MIP-1 beta, and RANTES, regulating immune cell migration and inflammatory responses . The receptor is primarily expressed on memory T lymphocytes, monocytes, and immature dendritic cells, where it participates in chemokine signaling pathways crucial for immune function . Additionally, like human CCR5, it can potentially serve as a coreceptor for certain simian immunodeficiency viruses (SIVs), making it significant in viral pathogenesis research .

How does Trachypithecus francoisi CCR5 compare to human CCR5 at the sequence level?

Trachypithecus francoisi CCR5 shares high sequence homology with human CCR5, reflecting evolutionary conservation across primate species . Nucleotide and amino acid sequence analyses reveal that primate CCR5 proteins are highly homologous, with variations slightly concentrated at the amino and carboxyl termini regions . One particularly important feature is the presence of Asp13 in Trachypithecus francoisi CCR5, a site that is critical for CD4-independent binding of SIV gp120 to Macaca mulatta CCR5 . This conservation suggests functional similarity in virus-receptor interactions across different primates, though species-specific differences may exist in binding affinity and downstream signaling pathways . The high degree of conservation in the transmembrane domains indicates the structural importance of these regions for maintaining receptor function, while the terminal regions show greater variability, potentially reflecting species-specific adaptations to different ligands or pathogens . These comparative sequence analyses provide valuable insights for researchers studying cross-species viral transmission and the evolution of host-pathogen interactions .

What expression systems are commonly used for producing recombinant Trachypithecus francoisi CCR5?

The most widely employed expression system for producing recombinant Trachypithecus francoisi CCR5 is Escherichia coli, which offers advantages in terms of scalability, cost-effectiveness, and relatively high protein yields . When expressing this seven-transmembrane protein in E. coli, researchers typically incorporate affinity tags such as polyhistidine (His) tags at the N-terminus to facilitate purification through immobilized metal affinity chromatography (IMAC) . The related Trachypithecus phayrei CCR5 has been successfully expressed as a full-length protein (1-352 amino acids) with an N-terminal His tag in E. coli, suggesting similar approaches would work for T. francoisi CCR5 . For proper folding of this complex membrane protein, expression conditions often require optimization of induction temperature, inducer concentration, and duration to minimize inclusion body formation . Alternative expression systems including yeast (Pichia pastoris or Saccharomyces cerevisiae), insect cells (Sf9 or Hi5), or mammalian cells (HEK293 or CHO) may provide better post-translational modifications and native-like folding, though with increased complexity and cost . The choice of expression system should be guided by the specific research application, whether structural studies, functional assays, or antibody production .

What methodological approaches are recommended for studying ligand binding properties of recombinant Trachypithecus francoisi CCR5?

Investigating the ligand binding properties of recombinant Trachypithecus francoisi CCR5 requires specialized techniques that preserve the native conformation of this seven-transmembrane receptor. Surface plasmon resonance (SPR) represents a powerful approach, where the purified recombinant CCR5 is immobilized on a sensor chip, allowing real-time monitoring of chemokine binding kinetics without the need for ligand labeling . Radioligand binding assays using 125I-labeled chemokines (such as 125I-MIP-1β) can provide quantitative binding parameters including dissociation constants (Kd), though these require appropriate safety measures for handling radioisotopes . Flow cytometry-based binding assays using fluorescently labeled chemokines offer an alternative approach when the receptor is expressed on cell surfaces, enabling analysis of binding in a more physiological membrane context . For higher throughput screening, researchers can employ functional ELISA methods, where immobilized CCR5 (approximately 10 μg/ml) is tested for binding to anti-CCR5 antibodies, with EC50 values typically in the range of 1.099-1.287 ng/mL for human CCR5 . When comparing binding properties across species, it's essential to maintain consistent experimental conditions and use appropriate controls, such as human CCR5 or other primate CCR5 variants, to identify species-specific differences in ligand recognition and binding affinity .

What are the recommended purification strategies for obtaining high-quality recombinant Trachypithecus francoisi CCR5 protein?

Purifying high-quality recombinant Trachypithecus francoisi CCR5 protein requires specialized approaches due to its hydrophobic transmembrane domains and complex structure. The initial purification typically employs immobilized metal affinity chromatography (IMAC) utilizing the N-terminal His-tag, with optimized buffers containing appropriate detergents such as n-dodecyl β-D-maltoside (DDM) or lauryl maltose neopentyl glycol (LMNG) to maintain protein solubility and native conformation . Following IMAC, size exclusion chromatography (SEC) is recommended to separate monomeric receptor from aggregates and to remove remaining contaminants, with typical buffer compositions including 20 mM Tris-HCl pH 8.0, 150 mM NaCl, and 0.03% DDM . For higher purity requirements, ion exchange chromatography can be incorporated as an intermediate step between IMAC and SEC, taking advantage of the protein's theoretical isoelectric point . Throughout the purification process, maintaining sample temperature at 4°C and including protease inhibitors helps minimize protein degradation . Quality assessment of the purified protein should include SDS-PAGE (aiming for >90% purity), Western blotting with anti-His antibodies, and functional binding assays to confirm biological activity . For long-term storage, the purified protein is best stabilized in PBS-based buffer containing 6% trehalose at pH 8.0, with aliquoting and storage at -80°C to avoid repeated freeze-thaw cycles that can compromise protein integrity .

What methodological challenges exist in studying the signaling pathways activated by Trachypithecus francoisi CCR5 and how can they be addressed?

Investigating signaling pathways activated by Trachypithecus francoisi CCR5 presents several methodological challenges that require sophisticated experimental approaches. The primary challenge stems from the need for expression systems that maintain the receptor in its native conformation while allowing detection of downstream signaling events, with cell lines derived from T. francoisi being ideal but rarely available . Researchers can address this by developing stable transfection systems in HEK293 or CHO cells expressing T. francoisi CCR5, coupled with pathway-specific reporter assays for G protein activation, calcium mobilization, or ERK/MAPK phosphorylation . Comparing signaling outcomes between human and T. francoisi CCR5 requires careful normalization for receptor expression levels, as variations in surface density can significantly impact signal magnitude independently of intrinsic signaling properties . Biased signaling—the preferential activation of certain pathways over others by specific ligands—presents another analytical challenge that necessitates multiparametric assays measuring multiple signaling endpoints simultaneously, such as bioluminescence resonance energy transfer (BRET) or fluorescence resonance energy transfer (FRET) techniques . The limited commercial availability of T. francoisi-specific signaling proteins and antibodies can be addressed by leveraging high sequence homology with human or macaque counterparts, verified through pilot experiments confirming cross-reactivity . RNA sequencing approaches comparing global transcriptional responses in cells expressing different primate CCR5 orthologs can reveal broader signaling networks and species-specific regulatory mechanisms that might be missed by targeted pathway analyses .

How can computational modeling and molecular dynamics simulations enhance our understanding of Trachypithecus francoisi CCR5 structure-function relationships?

Computational modeling and molecular dynamics simulations offer powerful approaches to elucidate structure-function relationships of Trachypithecus francoisi CCR5 at atomic resolution. Homology modeling, using human CCR5 crystal structures (PDB IDs: 4MBS, 6AKX) as templates, can generate reliable 3D models of T. francoisi CCR5, given the high sequence homology between primate CCR5 variants . These models can be refined through molecular dynamics simulations in explicit lipid bilayers over microsecond timescales, capturing conformational dynamics especially in the variable N-terminus and extracellular loops that mediate ligand recognition and viral glycoprotein binding . Docking simulations with chemokine ligands (MIP-1α, MIP-1β, RANTES) and viral envelope proteins can predict key interaction residues and binding energies, which can then be experimentally validated through site-directed mutagenesis and binding assays . Comparative simulations between human CCR5 and T. francoisi CCR5 can highlight species-specific differences in electrostatic surface potentials, binding pocket architecture, and allosteric communication networks within the receptor . Advanced simulation techniques such as Gaussian accelerated molecular dynamics (GaMD) or metadynamics can explore conformational transitions between active and inactive states, providing insights into activation mechanisms and potential species-specific signaling biases . Integration of these computational approaches with experimental data creates a powerful framework for understanding evolutionary adaptations in receptor function, designing selective ligands or inhibitors, and predicting cross-species viral transmission potential based on structural compatibility between viral envelope proteins and different primate CCR5 variants .

What are the optimal experimental designs for comparing functional differences between human and Trachypithecus francoisi CCR5?

Designing experiments to compare functional differences between human and Trachypithecus francoisi CCR5 requires careful consideration of expression systems, functional readouts, and appropriate controls. The optimal approach involves parallel expression of both receptors in the same cell background (typically HEK293 or CHO cells) using identical promoters and expression vectors, with equivalent expression levels confirmed by flow cytometry or quantitative Western blotting . Functional assays should encompass multiple aspects of receptor biology: chemokine binding (using competitive binding assays with radiolabeled or fluorescently labeled ligands), G protein activation (measured via [35S]GTPγS binding or BRET-based G protein dissociation assays), β-arrestin recruitment (using enzyme complementation or BRET techniques), and downstream signaling (calcium flux, ERK phosphorylation, gene expression) . To control for interspecies compatibility issues in signaling machinery, chimeric G proteins or human/T. francoisi chimeric receptors can isolate the contribution of specific receptor domains to observed functional differences . Viral coreceptor function should be assessed using pseudotyped lentiviral particles expressing different SIV or HIV envelope proteins, with infection efficiency quantified by reporter gene expression . Dose-response curves rather than single-point measurements are essential for detecting subtle differences in potency (EC50) or efficacy (Emax) between the two receptors across different ligands or viral strains . Statistical analysis should employ two-way ANOVA to simultaneously evaluate the effects of receptor type and ligand/virus variant, with multiple comparison corrections for the numerous parameters being tested .

What approaches can researchers use to investigate the role of post-translational modifications in Trachypithecus francoisi CCR5 function?

Investigating post-translational modifications (PTMs) of Trachypithecus francoisi CCR5 requires integrated approaches combining biochemical, mass spectrometry, and functional techniques. Researchers should begin with prediction algorithms to identify potential PTM sites (phosphorylation, sulfation, glycosylation, palmitoylation) based on sequence analysis, followed by experimental verification . Site-directed mutagenesis of predicted PTM sites (converting serines/threonines to alanines for phosphorylation sites, tyrosines to phenylalanines for sulfation sites, cysteines to serines for palmitoylation sites, or asparagines to glutamines for N-glycosylation sites) allows assessment of their functional importance in receptor expression, trafficking, ligand binding, and signaling . Mass spectrometry analysis of purified receptor provides direct identification of PTMs, with approaches such as enrichment strategies for phosphopeptides, titanium dioxide chromatography, or immunoprecipitation with PTM-specific antibodies enhancing detection sensitivity . Expression systems significantly impact PTM patterns—E. coli lacks most eukaryotic PTM machinery, while insect cells have limited glycosylation capabilities compared to mammalian cells . For studying dynamic regulation, researchers can employ metabolic labeling with 32P-orthophosphate to track phosphorylation changes after receptor activation, or pulse-chase experiments with [35S]cysteine/methionine to monitor receptor maturation and trafficking . Comparative analysis between human and T. francoisi CCR5 can reveal species-specific differences in PTM patterns and their functional consequences, potentially explaining differences in ligand selectivity, signaling bias, or viral coreceptor function . These approaches provide mechanistic insights into how PTMs regulate CCR5 function across different primate species, potentially revealing novel therapeutic targets for modulating receptor activity .

What can we learn from comparing the structural and functional properties of recombinant CCR5 proteins from different Trachypithecus species?

Comparative analysis of recombinant CCR5 proteins from different Trachypithecus species, including T. francoisi and T. phayrei, offers valuable insights into receptor evolution within this primate genus. The amino acid sequence of T. phayrei CCR5 (O97879) has been documented as a 352-residue protein, providing a reference point for structural comparison with T. francoisi CCR5 . Sequence alignment between these closely related species reveals regions of absolute conservation versus areas of divergence, with the latter potentially indicating species-specific adaptations to different environmental or pathogenic pressures . Functional comparisons through binding assays with chemokines and viral envelope proteins can reveal subtle differences in ligand selectivity, binding kinetics, or signaling outcomes that may correlate with species-specific sequence variations . Expression studies comparing surface levels, internalization rates, and recycling dynamics between different Trachypithecus CCR5 variants might uncover differences in receptor regulation that impact immune cell function or viral susceptibility . Molecular modeling of these closely related CCR5 variants can highlight how even minor sequence differences translate to structural alterations that affect binding pocket geometry or transmembrane helix packing . These comparative analyses within the Trachypithecus genus provide a finer-grained evolutionary perspective than broader cross-genera comparisons, potentially revealing more recent adaptive changes and offering insights into the functional plasticity of CCR5 over shorter evolutionary timescales . Such information enhances our understanding of structure-function relationships in this important immune receptor and may guide the development of species-specific CCR5 modulators for research applications .