Recombinant Lophocebus aterrimus C-C chemokine receptor type 5 (CCR5)

What is CCR5 and what is its significance in Lophocebus aterrimus?

CCR5 (C-C chemokine receptor type 5) is a seven-transmembrane G protein-coupled receptor expressed primarily by T cells and macrophages. In Lophocebus aterrimus, as in other primates, CCR5 functions as a chemokine receptor that responds to ligands including MIP-1α, MIP-1β, and RANTES (CCL5) . The significance of studying CCR5 from Lophocebus aterrimus lies in comparative analysis with human CCR5, particularly in understanding species-specific differences in viral co-receptor function and immune responses. Unlike some other non-human primates such as red-capped mangabeys (which have a 24 bp deletion in their CCR5 gene), Lophocebus aterrimus possesses a functional CCR5 receptor that serves as a co-receptor for SIV infection .

How does the molecular structure of Lophocebus aterrimus CCR5 compare to human CCR5?

The molecular structure of Lophocebus aterrimus CCR5 shares significant homology with human CCR5, maintaining the characteristic seven-transmembrane domain structure typical of G protein-coupled receptors. While specific structural data for Lophocebus aterrimus CCR5 is limited in the literature, research indicates that primate CCR5 proteins generally consist of approximately 352-355 amino acids with a molecular weight of around 40.5 kDa .

The key differences between Lophocebus aterrimus CCR5 and human CCR5 likely occur in the N-terminal domain and extracellular loops, which are critical for ligand binding and co-receptor function. These structural variations may influence:

• Binding affinity for natural chemokine ligands

• Interaction with viral envelope proteins

• Response to synthetic antagonists and inhibitors

• Post-translational modifications, particularly sulfation patterns

Understanding these structural differences is essential for interpreting experimental results when using Lophocebus aterrimus CCR5 as a model for human CCR5 function or when studying species-specific differences in SIV/HIV pathogenesis.

What are the principal applications of recombinant Lophocebus aterrimus CCR5 in HIV/SIV research?

Recombinant Lophocebus aterrimus CCR5 serves several critical functions in HIV/SIV research:

• Comparative virology studies: Investigating species-specific differences in co-receptor usage between different SIV strains and HIV variants . This is particularly valuable for understanding viral tropism and host adaptation.

• Evolution of viral resistance: Analyzing how structural differences in mangabey CCR5 compared to human CCR5 might influence susceptibility or resistance to specific viral strains .

• Drug development platforms: Testing CCR5 antagonists and entry inhibitors across different primate CCR5 variants to identify broadly effective therapeutic candidates.

• Structural biology research: Using recombinant protein for crystallography or cryo-EM studies to determine species-specific structural features.

• Immunological research: Investigating differences in chemokine signaling pathways between human and non-human primate immune cells.

The natural hosts of SIV infection typically do not develop AIDS-like illness despite sustained viral replication, making comparative studies between human and non-human primate CCR5 particularly valuable for understanding pathogenesis mechanisms .

What expression systems are most effective for producing functional recombinant Lophocebus aterrimus CCR5?

The choice of expression system significantly impacts the structural integrity and functionality of recombinant Lophocebus aterrimus CCR5. Based on available data, researchers have multiple options:

For studies requiring functional CCR5 that accurately mimics the native receptor for signaling or binding studies, mammalian expression systems are generally preferred despite their higher cost and lower yield . For structural studies requiring large quantities of protein where post-translational modifications are less critical, E. coli or yeast systems may be more suitable.

How can researchers verify the functionality of recombinant Lophocebus aterrimus CCR5?

Verifying the functionality of recombinant Lophocebus aterrimus CCR5 requires a multi-faceted approach:

• Ligand binding assays: Using fluorescently labeled chemokines (MIP-1α, MIP-1β, RANTES) to measure binding affinity and specificity. Competition binding assays with unlabeled ligands can provide quantitative binding parameters .

• Calcium flux assays: Measuring intracellular calcium mobilization following ligand binding to confirm signal transduction capability.

• Chemotaxis assays: Evaluating the ability of the recombinant receptor to induce directional migration when expressed in appropriate cell lines.

• Co-receptor function assays: Testing the ability of the recombinant receptor to support SIV entry in cell-based assays, particularly important for comparative virology studies .

• Antagonist inhibition studies: Confirming that known CCR5 antagonists (like maraviroc) bind and block function in a dose-dependent manner. The study by Pierre Calmet (2020) demonstrated that cholesterol considerably decreases maraviroc binding affinity to CCR5 receptors, suggesting that lipid composition should be carefully controlled in these assays .

Researchers should include appropriate positive controls (such as human CCR5) and negative controls (non-transfected cells or cells expressing irrelevant receptors) in all functional assays.

What insights can be gained from studying the genetic variations in CCR5 across different primate species?

Studying genetic variations in CCR5 across primate species provides valuable insights into:

• Evolutionary adaptation to pathogens: The CCR5-Δ32 mutation in humans and the 24 bp deletion in red-capped mangabeys suggest convergent evolution in response to selective pressure from pathogens . These natural genetic knockouts serve as models for understanding resistance mechanisms.

• Host-pathogen co-evolution: Differences in CCR5 sequence and expression between primate species that are natural SIV hosts versus those that develop AIDS-like illness help elucidate factors contributing to non-pathogenic infection .

• Novel therapeutic approaches: Genetic variants that confer resistance to viral infection without compromising immune function identify potential targets for therapeutic intervention. The success of CCR5-Δ32 homozygous stem cell transplants in "curing" HIV infection in at least five patients demonstrates the translational potential of this research .

• Functional constraints on receptor evolution: Conserved regions across primate CCR5 variants highlight domains essential for chemokine signaling that cannot be altered without compromising immune function.

A comprehensive comparative genomics approach examining CCR5 variants across primate lineages, including Lophocebus aterrimus, provides a natural laboratory for understanding both pathogen resistance mechanisms and chemokine biology.

How does receptor sulfation affect the binding properties of Lophocebus aterrimus CCR5 compared to human CCR5?

Receptor tyrosine sulfation plays a critical role in chemokine binding and HIV/SIV co-receptor function. While specific data on Lophocebus aterrimus CCR5 sulfation is limited, research on human CCR5 provides important insights that can guide comparative studies:

• Sulfation heterogeneity: Evidence suggests CCR5 sulfation is heterogeneous, creating subpopulations of receptors with different binding properties . This heterogeneity likely extends to Lophocebus aterrimus CCR5, potentially with species-specific patterns.

• Impact on ligand binding: Studies have shown that the anti-HIV chemokine analog 5P12-RANTES owes its enhanced inhibitory activity to its capacity to bind a larger pool of differently sulfated CCR5 receptors than native chemokines like CCL5 .

• Methodological approach: To investigate sulfation differences between human and Lophocebus aterrimus CCR5, researchers can:

  • Perform ELISA assays on synthetic N-terminal sulfopeptides

  • Conduct binding assays under conditions that modulate CCR5 sulfation levels

  • Compare antibody recognition of differently sulfated receptor populations

  • Use mass spectrometry to map and quantify sulfation sites

Understanding species-specific differences in CCR5 sulfation patterns may reveal important insights into differential susceptibility to SIV/HIV infection and disease progression.

What role does the lipid environment play in the function of recombinant Lophocebus aterrimus CCR5?

The lipid environment significantly impacts CCR5 function and ligand interactions, as demonstrated in studies with human CCR5:

• Cholesterol effects: Research has shown that cholesterol considerably decreases maraviroc binding affinity to CCR5 receptors . This suggests that the lipid composition of the membrane environment is a critical factor in drug binding studies and potentially in natural ligand interactions.

• Reconstitution systems: When designing experiments with recombinant Lophocebus aterrimus CCR5, researchers should consider using reconstituted model lipid systems of controlled composition. Studies have successfully employed such systems with CCR5 from different expression sources including Pichia pastoris and cell-free expression .

• Conformational dynamics: Coarse-grained molecular dynamics simulations have demonstrated that cholesterol impacts receptor-conformational flexibility and dynamics . This suggests that differences in membrane composition between experimental systems may lead to different functional outcomes.

• Experimental considerations:

  • Control lipid composition in binding assays

  • Consider native-like lipid environments for functional studies

  • Compare results across different membrane compositions

  • Use techniques like plasmon waveguide resonance and fluorescence anisotropy to characterize receptor/ligand interactions in defined lipid environments

These considerations are particularly important when comparing results across different experimental systems or when attempting to correlate in vitro findings with in vivo biology.

What purification strategies yield the highest purity and functionality for recombinant Lophocebus aterrimus CCR5?

Purifying functional membrane proteins like CCR5 presents significant challenges. Based on established protocols for similar GPCRs, the following strategies are recommended:

• Affinity chromatography: Using tag systems appropriate to the expression system (His-tag, FLAG-tag, or biotin-Avi-tag approaches). For biotin-tagged proteins, the E. coli biotin ligase (BirA) system can be employed to specifically biotinylate the AviTag peptide during in vivo expression .

• Size exclusion chromatography: Following affinity purification, size exclusion chromatography helps remove aggregates and ensure a homogeneous preparation. Sucrose gradient ultracentrifugation has also been successfully used to purify CCR5 .

• Detergent selection: The choice of detergent for solubilization and purification is critical. Mild detergents like n-dodecyl-β-D-maltoside (DDM) and lauryl maltose neopentyl glycol (LMNG) better preserve protein structure and function compared to harsher alternatives.

• Lipid supplementation: Adding specific lipids during purification can maintain receptor stability and function. Cholesterol and phospholipids with defined acyl chain compositions help preserve native-like properties.

• Quality control: Assess protein purity by SDS-PAGE (>85% purity is typically considered acceptable) , and evaluate functionality through binding assays with known ligands.

The specific approach should be tailored to the downstream application, with more stringent purification required for structural studies than for initial binding assays.

How can researchers optimize expression conditions to improve yield and quality of recombinant Lophocebus aterrimus CCR5?

Optimizing expression conditions is essential for obtaining sufficient quantities of functional protein:

For all systems, codon optimization for the expression host can significantly improve yields. Additionally, incorporating stabilizing mutations or fusion partners may enhance expression without compromising function.

Quality control should include not only quantity assessments (e.g., total protein yield) but also functional assays to ensure the recombinant protein maintains native-like binding and signaling properties.

What are the most common challenges in working with recombinant Lophocebus aterrimus CCR5 and how can they be addressed?

Working with recombinant CCR5 presents several challenges:

• Low expression levels:

  • Solution: Screen multiple expression systems and conditions; consider using expression enhancers or chaperones; optimize codon usage for the expression host.

• Protein misfolding:

  • Solution: Express at lower temperatures; use protein stabilization additives; consider fusion partners that enhance folding; optimize detergent selection for membrane extraction.

• Heterogeneous post-translational modifications:

  • Solution: Select expression systems capable of appropriate modifications; purify specific subpopulations using techniques like ion exchange chromatography; characterize modification patterns by mass spectrometry.

• Aggregation during storage:

  • Solution: Optimize buffer conditions; add stabilizing agents like glycerol; store at appropriate concentration (typically 1-5 mg/ml); consider flash-freezing aliquots rather than repeated freeze-thaw cycles.

• Lipid dependency for function:

  • Solution: Reconstitute in defined lipid environments; supplement purification buffers with specific lipids; use nanodiscs or liposomes for functional studies.

• Variability in binding assays:

  • Solution: Standardize experimental conditions; include appropriate controls; account for receptor heterogeneity in data analysis; consider competition binding assays rather than direct binding for more reliable results .

By anticipating these challenges and implementing appropriate strategies, researchers can improve the consistency and reliability of their work with recombinant Lophocebus aterrimus CCR5.

How do functional assays with Lophocebus aterrimus CCR5 compare with those using human CCR5?

When conducting parallel studies with Lophocebus aterrimus CCR5 and human CCR5, researchers should consider:

• Binding kinetics differences: Variations in association and dissociation rates for chemokines and inhibitors may exist between species variants. These differences should be systematically characterized through competition binding assays .

• Signaling pathway variations: While the core G-protein signaling machinery is conserved, species-specific differences in coupling efficiency or bias toward different downstream pathways may exist. Calcium flux, ERK phosphorylation, and β-arrestin recruitment assays should be compared across species variants.

• Viral entry efficiency: When using CCR5 as a co-receptor for viral entry studies, efficiency may differ between species variants. Quantitative entry assays with pseudotyped viruses can help characterize these differences.

• Antagonist sensitivity: Response to inhibitors like maraviroc may vary between human and Lophocebus aterrimus CCR5. Full dose-response curves should be generated to determine IC50 values and efficacy parameters.

• Data standardization: To make valid comparisons, researchers should:

  • Use the same expression system for both proteins

  • Normalize for surface expression levels

  • Maintain consistent experimental conditions

  • Use internal standards across experiments

  • Present data as relative values when appropriate

These comparative studies are particularly valuable for understanding species-specific differences in HIV/SIV pathogenesis and for developing broadly effective antiviral strategies.

What genetic variations in Lophocebus aterrimus CCR5 might impact experimental outcomes compared to other primate CCR5 variants?

Genetic variations in CCR5 across primate species can significantly impact experimental outcomes:

• N-terminal domain variations: The N-terminus contains critical binding determinants for both chemokines and viral envelope proteins. Sequence differences in this region may alter binding affinity and specificity.

• Sulfation patterns: Tyrosine sulfation heterogeneity affects binding properties . Different primate species may have different patterns or efficiency of tyrosine sulfation.

• Transmembrane domain differences: Mutations in transmembrane domains can affect receptor conformation, G-protein coupling, and antagonist binding.

• Deletion mutations: Some primates carry deletion mutations similar to the human CCR5-Δ32. The red-capped mangabey has a 24 bp deletion in CCR5, causing it to use CCR2b as the coreceptor for SIV entry instead .

To account for these variations in experimental design:

• Sequence the specific Lophocebus aterrimus CCR5 variant being used

• Compare key functional domains with other primate CCR5 sequences

• Consider how identified variations might affect the specific interaction being studied

• Include appropriate controls (human CCR5, other primate variants) in parallel experiments

• Interpret results in the context of known sequence differences

Understanding the specific sequence and functional differences of the Lophocebus aterrimus CCR5 variant being studied is essential for accurate data interpretation and cross-species comparisons.

What emerging technologies are advancing research with recombinant primate CCR5 proteins?

Several emerging technologies are revolutionizing CCR5 research:

• Cryo-EM for membrane protein structural biology: Advances in cryo-electron microscopy now enable high-resolution structural determination of membrane proteins like CCR5 in various conformational states and in complex with ligands.

• CRISPR-based approaches: Precise genome editing allows creation of chimeric receptors or introduction of specific mutations to study structure-function relationships across species variants.

• Single-molecule methods: Techniques like single-molecule FRET and super-resolution microscopy provide insights into conformational dynamics and oligomerization states of CCR5 in different lipid environments.

• Native mass spectrometry: Advances in this field now allow analysis of intact membrane proteins with associated lipids and post-translational modifications.

• Nanobody technology: Development of camelid antibody fragments (nanobodies) that recognize specific conformational states of GPCRs provides new tools for stabilizing and studying receptor conformations.

• Computational approaches: Molecular dynamics simulations and machine learning methods enable prediction of species-specific differences in ligand binding and receptor function, guiding experimental design.

These technologies offer unprecedented opportunities to understand the structural and functional properties of Lophocebus aterrimus CCR5 and other primate variants, advancing both basic research and therapeutic development.

How might research with Lophocebus aterrimus CCR5 contribute to HIV/AIDS treatment strategies?

Research with Lophocebus aterrimus CCR5 has several potential applications for HIV/AIDS treatment development:

• Novel antagonist discovery: Comparative binding studies across primate CCR5 variants can identify conserved binding pockets for the development of broadly effective entry inhibitors with higher genetic barriers to resistance.

• Understanding natural resistance: Studies of SIV infection in natural hosts like mangabeys, which typically don't progress to AIDS despite high viral loads, may reveal protective mechanisms that could be therapeutically mimicked .

• Gene therapy approaches: The success of CCR5-Δ32 homozygous stem cell transplants in producing HIV-cleared AIDS patients ("cures") suggests that engineered disruption of CCR5 function remains a promising approach. Understanding species-specific differences in CCR5 function may identify more precise modifications with fewer side effects.

• Immunomodulatory strategies: CCR5's role in inflammatory responses suggests that targeted modulation could address HIV-associated inflammation without completely blocking receptor function.

• Broad-spectrum antiviral approaches: Since CCR5 serves as a co-receptor for multiple pathogens , studies across primate species may identify common mechanisms of viral entry that could be targeted for broad-spectrum antiviral development.