Recombinant Pongo pygmaeus C-C chemokine receptor type 5 (CCR5)

What is Pongo pygmaeus CCR5 and how does it compare to human CCR5?

Pongo pygmaeus (Bornean orangutan) CCR5 is a chemokine receptor belonging to the G protein-coupled receptor family with seven transmembrane domains. When compared with human CCR5 and other primate CCR5 sequences, the nucleotide and amino acid sequences are highly homologous. Studies show that variations between orangutan and human CCR5 are slightly concentrated at the amino and carboxyl termini of the protein . This high degree of conservation suggests important functional roles for CCR5 in primates that have been maintained throughout evolution.

The orangutan CCR5 contains site Asp13, which is critical for CD4-independent binding of SIV gp120 to macaque CCR5. This site is also present in other nonhuman primates, suggesting that orangutan CCR5 might also bind SIV gp120 without requiring CD4 . This characteristic distinguishes nonhuman primate CCR5 from the human version and may have implications for understanding viral binding mechanisms.

What are the recommended expression systems for recombinant Pongo pygmaeus CCR5?

While the search results don't specifically address expression systems for orangutan CCR5, recombinant human CCR5 has been successfully produced in E. coli with His-tags for purification and detection . Based on the high homology between human and orangutan CCR5, similar expression systems could be applied with species-specific modifications.

For expressing recombinant Pongo pygmaeus CCR5, researchers should consider:

• Bacterial expression systems (E. coli) for producing segments or modified versions of the protein

• Mammalian expression systems (CHO, HEK293) for full-length functional studies that require proper folding and post-translational modifications

• Expression with fusion tags (His, GST) to facilitate purification

Depending on the experimental requirements, the CCR5 can be expressed alone or co-expressed with CD4 if studying interactions that might require both receptors . When expressing membrane proteins like CCR5, special attention should be paid to proper folding and membrane insertion to maintain functionality.

What purification methods are effective for recombinant orangutan CCR5?

Based on protocols used for human CCR5, purification of recombinant orangutan CCR5 would likely involve:

• Affinity chromatography using the fusion tag (e.g., His-tag)

• Size exclusion chromatography to separate the target protein from contaminants

• Ion exchange chromatography for further purification if needed

For His-tagged recombinant CCR5, immobilized metal affinity chromatography (IMAC) using Ni-NTA resin would be the primary purification method . The purified protein should be stored in a suitable buffer, such as PBS containing stabilizing agents like trehalose (5%) and reducing agents like DTT (1mM) to maintain protein stability .

Quality control should include SDS-PAGE and Western blot to confirm purity (target >97%), as well as endotoxin testing using the LAL method to ensure levels below 1.0EU per 1μg for research applications .

How stable is purified recombinant CCR5 and what are the optimal storage conditions?

Based on data from human recombinant CCR5, which shares high homology with orangutan CCR5, the following storage recommendations apply:

• Short-term storage (up to one month): 2-8°C

• Long-term storage (up to 12 months): Aliquot and store at -80°C

• Avoid repeated freeze/thaw cycles to maintain protein integrity

Thermal stability testing through accelerated degradation (37°C for 48 hours) shows that properly stored CCR5 should demonstrate a loss rate of less than 5% within the expiration date . For reconstitution, PBS or similar buffers are recommended, and the addition of stabilizing agents like trehalose and preservatives like Proclin300 can help maintain protein integrity .

What methods can be used to study orangutan CCR5 internalization following ligand binding?

To study CCR5 internalization in orangutan cells or recombinant systems expressing orangutan CCR5, researchers can adapt protocols used for human CCR5 studies:

• Flow cytometry-based internalization assays:

  • Prepare cells expressing orangutan CCR5 at a concentration of 10⁶ cells/ml

  • Treat cells with chemokines (typically 50 nM) for various timepoints at 37°C

  • Wash cells with cold PBS or PBS containing 1% FCS and 1% NaN₃

  • Detect surface CCR5 using anti-CCR5 monoclonal antibodies followed by fluorophore-conjugated secondary antibodies

  • Quantify using flow cytometry and analyze with appropriate software

• Fluorescence microscopy:

  • Express fluorescently tagged orangutan CCR5 or use antibody labeling

  • Track receptor movement following chemokine exposure

  • Quantify the percentage of internalized receptor over time

When studying orangutan CCR5, it's important to verify antibody cross-reactivity or develop orangutan-specific antibodies, as most commercially available antibodies are designed for human CCR5. Based on studies with human CCR5, chemokines like MIP-1α, MIP-1β, and RANTES at 50 nM concentration would be expected to induce approximately 50% internalization of the receptor, while MCP-2, MCP-3, and MCP-4 might induce less internalization (approximately 20%) .

How can researchers investigate phosphorylation patterns of orangutan CCR5?

To study the phosphorylation of orangutan CCR5, researchers should consider:

• Phosphorylation-specific detection methods:

  • Immunoprecipitation followed by Western blot with phospho-specific antibodies

  • Mass spectrometry to identify specific phosphorylated residues

  • Radioactive labeling with ³²P for quantitative phosphorylation studies

• Kinase identification experiments:

  • In vitro kinase assays with purified kinases and recombinant CCR5

  • Kinase inhibitor screens to identify involved signaling pathways

Based on human CCR5 studies, chemokines like MIP-1α, MIP-1β, and RANTES (at 50 nM) would be expected to induce phosphorylation, while other chemokines like MCP-2, MCP-3, and MCP-4 might not induce significant phosphorylation . These findings provide a starting point for comparative studies with orangutan CCR5, though species-specific differences may exist.

When designing these experiments, researchers should consider creating phosphorylation-deficient mutants of orangutan CCR5 to study the functional significance of specific phosphorylation events.

What approaches are recommended for studying the evolutionary rate and selective pressures on orangutan CCR5?

To study evolutionary rates and selective pressures on orangutan CCR5:

• Sequence comparison and phylogenetic analysis:

  • Collect CCR5 sequences from multiple primate species, including various great apes

  • Align sequences and construct phylogenetic trees using maximum likelihood or Bayesian methods

  • Compare topologies with established primate phylogenies to identify discrepancies

• Calculate evolutionary rates:

  • Determine synonymous (Ks) and nonsynonymous (Ka) substitution rates

  • Calculate Ka/Ks ratios to assess selective pressure (Ka/Ks < 1 indicates purifying selection)

  • Compare rates between different primate lineages

• Functional validation of variant sites:

  • Express recombinant CCR5 variants with specific substitutions

  • Test functional differences in ligand binding or signaling

  • Correlate functional changes with evolutionary patterns

Research on primate CCR5 has shown that the synonymous mutation rate in primates is constant at approximately 1.1 × 10⁻⁹ synonymous mutations per site per year . Comparisons of Ka and Ks suggest that CCR5 genes have undergone negative or purifying selection. Interestingly, Ka/Ks ratios from cercopithecines and colobines are significantly different, implying that selective pressures have played different roles in these lineages .

These approaches can help determine whether orangutan CCR5 has been subject to unique selective pressures compared to other great apes or more distant primate relatives.

How can researchers evaluate the interaction between orangutan CCR5 and viral envelope proteins?

To study interactions between orangutan CCR5 and viral envelope proteins such as SIV gp120:

• Binding assays:

  • Surface Plasmon Resonance (SPR) to measure binding kinetics

  • ELISA-based binding assays with recombinant proteins

  • Flow cytometry with cells expressing orangutan CCR5

• Functional assays:

  • Cell fusion assays to assess co-receptor function

  • Viral entry assays using pseudotyped viruses

  • Competitive binding studies with known CCR5 ligands

• Structural approaches:

  • Molecular modeling based on sequence homology

  • X-ray crystallography or cryo-EM of protein complexes

  • Mutagenesis studies to identify critical binding residues

The presence of Asp13 in orangutan CCR5, which is critical for CD4-independent binding of SIV gp120 to macaque CCR5, suggests that orangutan CCR5 might bind SIV gp120 without the presence of CD4 . This characteristic could be experimentally verified using binding assays with recombinant proteins or cell-based assays with orangutan CCR5-expressing cells.

Researchers should consider creating chimeric receptors between human and orangutan CCR5 to identify regions responsible for differential binding or functional properties related to viral interactions.

What are the implications of CCR5 polymorphisms in orangutans for viral resistance studies?

To investigate CCR5 polymorphisms in orangutans and their implications for viral resistance:

• Population genetics approaches:

  • Sequence CCR5 from multiple orangutan individuals from different populations

  • Identify and characterize polymorphisms, focusing on coding regions

  • Calculate population genetics parameters (heterozygosity, FST, Tajima's D)

• Functional studies of variants:

  • Express variant forms of orangutan CCR5 in cell lines

  • Test receptor function, including ligand binding, signaling, and internalization

  • Assess co-receptor function for different viral strains

• Comparative studies with human CCR5Δ32:

  • Search for similar loss-of-function variants in orangutan populations

  • Compare functional consequences of any identified variants

The human CCR5Δ32 mutation provides resistance to HIV infection by preventing the expression of functional CCR5 on the cell surface . No equivalent mutation has been documented in orangutans, but systematic screening of orangutan populations could reveal natural polymorphisms with potential implications for viral resistance.

How can orangutan CCR5 be used in comparative studies of primate immune function?

Orangutan CCR5 can serve as a valuable tool in comparative immunology studies:

• Cross-species functional comparison:

  • Express recombinant CCR5 from orangutans alongside human and other primate CCR5 in consistent cell systems

  • Compare ligand binding affinities using the same panel of chemokines

  • Assess signaling pathways activated by receptor stimulation

• Evolutionary adaptation analysis:

  • Identify amino acid differences between orangutan and other primate CCR5 sequences

  • Correlate structural differences with functional variations

  • Link differences to potential selection pressures from pathogens

• Cell-type specific expression studies:

  • Compare CCR5 expression patterns across immune cell types in different primates

  • Analyze regulatory regions for conserved and divergent elements

Studies of CCR5 across primate species have shown interesting variations in function. For example, the differential responses to various chemokines observed in human CCR5 (with MIP-1α, MIP-1β, and RANTES inducing stronger responses than MCP-2, MCP-3, and MCP-4) provide a framework for comparative studies with orangutan CCR5.

The high homology between primate CCR5 sequences, with variations concentrated at the amino and carboxyl termini , suggests that specific regions might be responsible for species-specific functional differences. Targeted mutagenesis of these regions in orangutan CCR5 could help identify determinants of species-specific receptor properties.

What role might orangutan CCR5 play in understanding resistance to neurotropic flaviviruses?

Research on orangutan CCR5 could contribute to understanding resistance to neurotropic flaviviruses:

• Comparative susceptibility studies:

  • Express orangutan CCR5 in relevant cell lines

  • Challenge with various flaviviruses (WNV, JEV, TBEV)

  • Compare infection rates and viral replication to human CCR5-expressing cells

• Leukocyte trafficking analysis:

  • Study the role of orangutan CCR5 in directing immune cell migration

  • Compare with human CCR5 function in similar contexts

  • Assess regulatory T-cell migration patterns

• Population genetics approaches:

  • Screen orangutan populations for CCR5 polymorphisms

  • Correlate with geographic distribution of flaviviruses

  • Assess evolutionary patterns in regions with endemic flavivirus presence

Studies in humans and mice have shown that CCR5 deficiency increases susceptibility to neurotropic flaviviruses like West Nile virus . In mice infected with Japanese encephalitis virus (JEV), CCR5 directs regulatory T-cell migration to the CNS . Similar studies involving orangutan CCR5 could reveal whether this protective mechanism is conserved across primate species.

The role of CCR5 has also been evaluated in the context of tick-borne encephalitis viruses, with CCR5-deficient mice showing decreased survival rates (48% vs. 90% in wild-type mice) when infected with Langat virus . Comparative studies with orangutan CCR5 could provide insights into potential differences in flavivirus susceptibility across primate species.

What are the best approaches for developing orangutan-specific CCR5 antibodies?

To develop orangutan-specific CCR5 antibodies:

• Antigen design strategies:

  • Identify orangutan-specific epitopes through sequence alignment

  • Use synthetic peptides corresponding to unique regions

  • Express recombinant protein fragments as immunogens

• Antibody production methods:

  • Monoclonal antibody development using hybridoma technology

  • Phage display libraries for recombinant antibody selection

  • Polyclonal antibody production with purified proteins or peptides

• Validation techniques:

  • Flow cytometry with orangutan cells or CCR5-transfected cell lines

  • Western blot against recombinant orangutan CCR5

  • Immunoprecipitation followed by mass spectrometry

  • Cross-reactivity testing against human and other primate CCR5

When designing antibodies, researchers should consider the high homology between human and orangutan CCR5. Focusing on regions with amino acid differences, particularly at the amino and carboxyl termini where variations are concentrated , would be most likely to yield species-specific antibodies.

For functional studies, antibodies targeting different domains of the receptor (extracellular loops, transmembrane regions, intracellular domains) may provide tools for dissecting receptor topology and function.

What are the challenges in studying signaling pathways downstream of orangutan CCR5?

Studying signaling pathways downstream of orangutan CCR5 presents several challenges:

• Technical challenges:

  • Establishing appropriate cellular models expressing orangutan CCR5

  • Ensuring proper coupling to G proteins in heterologous expression systems

  • Developing assays sensitive enough to detect potentially subtle signaling differences

• Experimental approaches:

  • Calcium flux assays to measure G protein-coupled signaling

  • ERK phosphorylation assays for MAPK pathway activation

  • β-arrestin recruitment assays for desensitization pathways

  • Chemotaxis assays to assess functional outcomes of signaling

• Comparative analysis with human CCR5:

  • Express both receptors in the same cell background

  • Test with identical panels of ligands at matching concentrations

  • Control for receptor expression levels, which can affect signaling magnitude

Based on human CCR5 studies, researchers should examine whether MIP-1α, MIP-1β, RANTES, and MCP-2 stimulate calcium flux and other signaling events in cells expressing orangutan CCR5, as these chemokines have been shown to stimulate such responses in human CCR5-expressing cells .

When interpreting results, researchers should consider that differences in expression levels between CCR5 and CD4 (if co-expressed) can affect experimental outcomes, as observed in human CCR5 studies where CCR5 expression levels varied between cell lines .

What are the future research directions for studies involving orangutan CCR5?

Future research directions for orangutan CCR5 should build on our current understanding of primate CCR5 evolution and function:

• Comprehensive comparative studies:

  • Systematic comparison of CCR5 function across all great ape species

  • Investigation of species-specific viral interactions

  • Analysis of CCR5 polymorphisms in wild orangutan populations

• Disease susceptibility research:

  • Evaluation of orangutan CCR5's role in susceptibility to emerging viral diseases

  • Investigation of CCR5 function in orangutan models of infectious disease

  • Comparison of CCR5-mediated immune responses across primate species

• Integration with genomic and ecological data:

  • Correlation of CCR5 variants with orangutan population history

  • Investigation of selective pressures in different orangutan habitats

  • Integration with broader studies of immune system evolution in endangered primates