Recombinant Pan troglodytes C-C chemokine receptor type 5 (CCR5)

What is the genomic organization of Pan troglodytes CCR5 compared to human CCR5?

Pan troglodytes CCR5 shares significant genomic organization with human CCR5, both located on chromosome 3 with similar exon-intron structures. The most critical methodological approach to characterizing Pan troglodytes CCR5 involves comparative genomic analysis using bioinformatics tools similar to those employed for human CCR5 analysis. Researchers should employ multiple sequence alignment techniques to identify conserved regions and species-specific variations.

When analyzing the gene, consider that human CCR5 is located on the short arm (p) at position 21 on chromosome 3 . The comparative analysis should include examination of promoter regions, regulatory elements, and coding sequences to identify species-specific differences that may influence expression patterns and protein function. Conservation analysis typically reveals that transmembrane domains are highly conserved while extracellular loops show greater variability.

What expression systems are most effective for producing recombinant Pan troglodytes CCR5?

For effective recombinant expression of Pan troglodytes CCR5, mammalian expression systems generally yield superior results compared to bacterial or insect cell systems, particularly when proper folding and post-translational modifications are critical for functional studies.

Methodologically, HEK293 and CHO cell lines provide optimal platforms using vectors containing strong promoters (CMV or EF1α) and appropriate selection markers. The protocol should include:

• Optimization of codon usage for mammalian expression

• Inclusion of an N-terminal signal peptide to facilitate membrane localization

• Addition of C-terminal tags (His, FLAG) positioned to minimize interference with ligand binding

• Selection of stable cell lines expressing the receptor at physiological levels

For membrane protein purification, extraction conditions should be carefully optimized using mild detergents such as DDM or LMNG to maintain the native conformation of transmembrane helices identified in human CCR5 structural studies .

How can researchers verify proper folding and functionality of recombinant Pan troglodytes CCR5?

Verifying proper folding and functionality of recombinant Pan troglodytes CCR5 requires multiple complementary approaches:

Ligand Binding Assays: Utilize fluorescently-labeled natural ligands (CCL3, CCL4, CCL5) to assess binding affinity through flow cytometry or confocal microscopy. These chemokines are known cognate ligands for human CCR5 and likely bind Pan troglodytes CCR5 with similar specificity .

Calcium Flux Assays: Monitor intracellular calcium release following ligand binding using calcium-sensitive dyes (Fluo-4 AM). This approach confirms receptor coupling to G proteins and downstream signaling.

Surface Expression Analysis: Flow cytometry with conformation-specific antibodies that recognize properly folded extracellular domains.

G Protein Coupling Assays: Measure GTPγS binding to assess functional G protein interaction following ligand stimulation.

How do molecular dynamics simulations inform structure-function relationships in Pan troglodytes CCR5?

Molecular dynamics simulations represent a powerful computational approach to investigate structure-function relationships in Pan troglodytes CCR5. The methodology should be modeled after established approaches for human CCR5 that have successfully revealed critical conformational changes and binding pocket dynamics.

Start by generating a homology model based on human CCR5 crystal structures (PDB files 5UIW, 5T1A, 5LWE, and 4RWS) . The simulation protocol should include:

• Embedding the receptor in a phosphatidylethanolamine (PEA) lipid membrane

• System equilibration with explicit water molecules and physiological ion concentrations

• Production runs of at least 300 nanoseconds using established force fields (AMBER14)

• Analysis of trajectory data focusing on dynamic cross-correlation matrix (DCCM) calculations

Key analysis metrics should include transmembrane helix mobility, extracellular loop flexibility, and intracellular conformational changes that may influence G protein coupling. Simulations should be run both with and without bound ligands to capture induced-fit effects.

Molecular dynamics simulations of human CCR5 have revealed amino acids with correlation coefficients >0.9 in dynamic cross-correlation matrix calculations, highlighting residues critical for conformational changes during signaling . Similar analysis of Pan troglodytes CCR5 would identify conserved dynamic networks and species-specific differences.

What role do post-translational modifications play in Pan troglodytes CCR5 function?

Post-translational modifications (PTMs) critically influence CCR5 function, with several key sites identified in human CCR5 that likely have corresponding importance in Pan troglodytes CCR5:

Sulfation of N-terminal tyrosines: Employ mass spectrometry to identify sulfated tyrosines in the N-terminus, as these modifications are crucial for chemokine binding. Methodologically, enrich for sulfated peptides using titanium dioxide chromatography before MS analysis.

Palmitoylation of C-terminal cysteines: Analyze using click chemistry with alkyne-tagged palmitate analogs followed by fluorescent azide conjugation and gel electrophoresis.

Phosphorylation of serine/threonine residues: Phosphoproteomic analysis using TiO₂ enrichment followed by LC-MS/MS to identify phosphorylation sites involved in receptor desensitization and internalization.

O-linked glycosylation: Employ enzymatic deglycosylation combined with lectin affinity chromatography to characterize these modifications.

When investigating PTMs, researchers should consider the conservation of modification sites between human and Pan troglodytes CCR5, as these sites often correspond to functional domains identified in human CCR5, including extracellular, transmembrane, and intracellular regions with their specific PTMs .

How can single-cell RNA sequencing inform tissue-specific expression patterns of Pan troglodytes CCR5?

Single-cell RNA sequencing (scRNA-seq) provides unprecedented resolution for determining cell type-specific expression patterns of Pan troglodytes CCR5. Based on human and mouse CCR5 expression studies, the methodological approach should focus on immune cells and tissue-resident macrophages.

The experimental design should include:

• Tissue dissociation protocols optimized for each target tissue (blood, brain, lung, liver)

• FACS-based enrichment of potential CCR5-expressing cells

• 10X Genomics or Drop-seq platform for high-throughput single-cell capture

• Computational analysis pipeline for clustering and differential expression analysis

Human CCR5 studies have identified significant expression in T cells, macrophages, dendritic cells, eosinophils, and microglia . Analysis of mouse single-cell data from PanglaoDB has revealed CCR5 expression in macrophages across multiple tissues including liver, vessels, lung, and heart, as well as in microglia from brain tissue .

What strategies minimize protein degradation during purification of recombinant Pan troglodytes CCR5?

Minimizing degradation during purification of recombinant Pan troglodytes CCR5 requires a comprehensive strategy addressing multiple points in the workflow:

Buffer Optimization:

• Maintain pH 7.4 throughout purification to match physiological conditions

• Include protease inhibitor cocktail with emphasis on serine and cysteine protease inhibitors

• Add 10-20% glycerol to stabilize protein structure

• Include cholesterol or cholesteryl hemisuccinate (CHS) at 0.1% to mimic native membrane environment

Temperature Management:

• Perform all steps at 4°C

• Avoid freeze-thaw cycles by aliquoting purified protein

• For long-term storage, flash-freeze in liquid nitrogen and store at -80°C

Detergent Selection:

• Begin extraction with mild detergents like DDM, LMNG, or UDM

• Consider detergent exchange during purification to more stabilizing agents like GDN

• Maintain detergent concentration above critical micelle concentration (CMC)

Chromatography Sequence:

• Affinity chromatography using anti-tag antibodies or ligand-based columns

• Size exclusion chromatography to remove aggregates and degradation products

• Consider lipid nanodiscs or SMALPs for final preparation if functional studies are planned

Quality control should include SDS-PAGE with western blotting, mass spectrometry to confirm intact protein, and circular dichroism to assess secondary structure content. This approach mirrors techniques used in human CCR5 studies where molecular modeling employed merged PDB structures with energy minimization in lipid membranes .

What are the critical considerations for designing binding assays between Pan troglodytes CCR5 and HIV envelope proteins?

Designing binding assays between Pan troglodytes CCR5 and HIV envelope proteins requires careful consideration of multiple methodological factors:

Protein Preparation:

• Express CCR5 in mammalian cells to ensure native conformation and PTMs

• Purify HIV envelope proteins (gp120) with minimal denaturation

• Verify conformational integrity of both proteins before assays

Assay Formats:

• Surface Plasmon Resonance (SPR): Immobilize purified CCR5 on lipid-coated sensor chips using captured His-tags or biotinylation

• Fluorescence Resonance Energy Transfer (FRET): Label CCR5 and gp120 with compatible fluorophore pairs

• Cell-Based Binding: Express CCR5 on cell surface and use labeled gp120 with flow cytometry

• Enzyme-Linked Immunosorbent Assay (ELISA): Immobilize one protein and detect binding with antibodies

Critical Controls:

• Include human CCR5 as comparative control

• Use CCR5 antagonists (e.g., maraviroc) to confirm binding site specificity

• Include CD4 in assays as it facilitates gp120-CCR5 interaction

• Test multiple HIV strains (R5-tropic vs. X4-tropic)

Data Analysis:

• Calculate binding kinetics (kon, koff) and affinity constants (KD)

• Determine Hill coefficients to assess binding cooperativity

• Compare Pan troglodytes vs. human CCR5 binding parameters

Human CCR5 serves as the primary co-receptor for R5-tropic HIV-1 strains, and understanding the binding differences between human and Pan troglodytes CCR5 may illuminate the molecular basis for species-specific HIV susceptibility patterns .

How can researchers address solubility challenges when expressing recombinant Pan troglodytes CCR5?

Addressing solubility challenges for recombinant Pan troglodytes CCR5 requires systematic optimization of multiple parameters:

Expression Construct Design:

• Include solubility-enhancing fusion partners (MBP, SUMO, thioredoxin)

• Optimize codon usage for expression host

• Consider truncating N/C-terminal domains if they contribute to aggregation

• Include cleavable tags that can be removed after solubilization

Expression Conditions:

• Reduce induction temperature (16-20°C)

• Decrease inducer concentration

• Extend expression time (24-72 hours)

• Supplement media with ligands or antagonists that stabilize the receptor

Solubilization Strategy:

• Screen detergent panel (DDM, LMNG, DM, OG, Digitonin)

• Test detergent mixtures for synergistic effects

• Include cholesterol or CHS as membrane mimetics

• Add specific lipids (phosphatidylcholine, phosphatidylethanolamine)

Alternative Approaches:

• Cell-free expression systems with direct detergent incorporation

• Nanodisc or SMALP reconstitution

• Directed evolution for solubility-enhanced variants

Data from human CCR5 studies suggest that extraction in phosphatidylethanolamine membrane environments with pH 7.4 provides optimal conditions for maintaining protein structure and solubility . The molecular dynamics approach employed for human CCR5, with membrane embedding and extensive water solvation, provides a theoretical foundation for developing effective solubilization protocols for the chimpanzee homolog .

How can variants in Pan troglodytes CCR5 inform our understanding of HIV resistance mechanisms?

Investigating Pan troglodytes CCR5 variants provides crucial insights into HIV resistance mechanisms through comparative analysis with human variants, particularly the Delta32 mutation associated with HIV resistance in humans .

Methodological Approach:

• Comprehensive Variant Identification:

  • Whole genome sequencing of diverse chimpanzee populations

  • Targeted sequencing of CCR5 locus with long-read technologies

  • Comparison with human variant databases (gnomAD, TOPmed)

• Functional Characterization:

  • Express identified variants in cell lines

  • Measure HIV envelope binding affinity

  • Assess receptor internalization and signaling

  • Evaluate co-receptor function in pseudovirus entry assays

• Structural Impact Assessment:

  • Model effects of variants on protein structure

  • Perform molecular dynamics simulations of variant proteins

  • Analyze alterations in binding pocket geometry

  • Predict functional consequences using computational tools similar to PolyPhen2, Provean, SIFT, and Align-GVGD used for human variants

• Population Genetics Analysis:

  • Calculate allele frequencies in different chimpanzee populations

  • Detect signatures of selection at CCR5 locus

  • Compare evolutionary patterns with human populations

Human CCR5 studies have identified 403 unique variants with varying predicted functional impacts . Similar comprehensive analysis of Pan troglodytes CCR5 variants would reveal species-specific polymorphisms that might contribute to differential HIV susceptibility. The analysis should prioritize variants in functional domains identified in human CCR5 studies, particularly those affecting ligand binding and HIV co-receptor function.

What experimental approaches best reveal functional differences between human and Pan troglodytes CCR5?

Revealing functional differences between human and Pan troglodytes CCR5 requires multifaceted experimental approaches:

Ligand Binding and Signaling Assays:

• Compare binding affinities for natural chemokines (CCL3, CCL4, CCL5)

• Measure calcium flux amplitude and kinetics

• Assess ERK phosphorylation following stimulation

• Quantify receptor internalization rates

HIV Co-Receptor Function:

• Pseudotyped virus entry assays with various HIV-1 envelopes

• Single-cycle infection assays in matched cell lines

• Direct binding measurements between soluble gp120 and CCR5

Structural Biology Approaches:

• Cryo-EM or X-ray crystallography of both receptors

• Hydrogen-deuterium exchange mass spectrometry to identify dynamic regions

• Cross-linking mass spectrometry to map interaction surfaces

Chimeric Receptor Studies:

• Generate domain-swapped chimeras between human and chimpanzee CCR5

• Identify specific regions responsible for functional differences

• Create point mutations at divergent residues

These approaches should focus on the key functional domains of CCR5 identified in human studies, including the extracellular domains involved in ligand binding and the transmembrane regions that form the binding pocket for small molecule antagonists .

How do differences in CCR5 expression patterns between humans and chimpanzees contribute to immune function variations?

Understanding differences in CCR5 expression patterns between humans and chimpanzees requires comprehensive tissue and cell-type profiling:

Tissue Expression Profiling:

• Perform RNAseq and protein quantification across matched tissue panels

• Analyze expression in key immune compartments (blood, spleen, lymph nodes)

• Examine brain tissue expression, focusing on microglia

• Compare expression in disease-relevant tissues (lung, intestine)

Single-Cell Analysis:

• Implement scRNA-seq of immune cells from both species

• Identify cell populations with differential CCR5 expression

• Compare expression in tissue-resident macrophages and microglia

• Analyze regulatory T cell CCR5 expression patterns

Regulatory Mechanism Investigation:

• Compare promoter and enhancer landscapes

• Analyze transcription factor binding profiles

• Assess epigenetic modifications at CCR5 locus

• Evaluate microRNA regulation differences

Functional Consequences:

• Measure chemotactic responses to CCR5 ligands

• Assess inflammatory responses in tissue-specific models

• Compare immune cell homing patterns

• Evaluate responses to inflammatory challenges

Human studies have shown significant CCR5 expression in T cells, macrophages, dendritic cells, and microglia . Analysis of mouse single-cell data from PanglaoDB has identified CCR5 expression in macrophages across multiple tissues including liver, vessels, lung, heart, and brain microglia . Comparative analysis of Pan troglodytes would likely reveal both conserved and species-specific expression patterns with functional consequences for immune responses.