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

What is Pongo abelii CCR5 and how does it differ structurally from human CCR5?

Pongo abelii CCR5 is a G protein-coupled receptor found in Sumatran orangutans (Pongo abelii) that functions as a chemokine receptor. Structurally, it shares high homology with human CCR5, with the most notable variations concentrated at the amino and carboxyl termini. The protein consists of 352 amino acids and maintains the characteristic seven-transmembrane domain structure of G protein-coupled receptors .

Comparative sequence analysis reveals that like other primate CCR5 proteins, Pongo abelii CCR5 contains the critical Asp13 residue, which is important for CD4-independent binding of SIV gp120. This suggests potential functional similarity in viral interactions despite sequence differences .

How should recombinant Pongo abelii CCR5 be stored and handled to maintain integrity?

Recombinant Pongo abelii CCR5 requires careful storage and handling to maintain protein integrity. The lyophilized protein should be stored at -20°C/-80°C upon receipt. For optimal stability, the following protocol is recommended:

• Briefly centrifuge the vial before opening to bring contents to the bottom

• Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 5-50% (50% is typically recommended)

• Aliquot for long-term storage at -20°C/-80°C

• Avoid repeated freeze-thaw cycles as this degrades protein quality

For working solutions, aliquots can be stored at 4°C for up to one week. The protein is typically supplied in a Tris/PBS-based buffer with 6% trehalose at pH 8.0 .

What expression systems are most effective for producing recombinant Pongo abelii CCR5?

Escherichia coli (E. coli) has been successfully employed as an expression system for recombinant Pongo abelii CCR5, particularly when the protein is tagged with an N-terminal histidine tag. This approach facilitates downstream purification and characterization processes .

For researchers seeking alternative expression systems, several considerations should be evaluated:

E. coli remains the most commonly used system due to its balance of yield and cost-effectiveness for structural and biochemical studies .

What purification strategy yields the highest purity for recombinant Pongo abelii CCR5?

Purification of His-tagged recombinant Pongo abelii CCR5 typically involves immobilized metal affinity chromatography (IMAC) followed by additional purification steps. A recommended protocol includes:

• Immobilized metal affinity chromatography (IMAC) using Ni-NTA resin

• Washing with increasing concentrations of imidazole to remove non-specifically bound proteins

• Elution with high imidazole concentration buffer

• Size exclusion chromatography for further purification

• Quality assessment using SDS-PAGE to confirm purity greater than 90%

The specific buffers and conditions may need optimization based on the expression system and downstream applications. The final product should demonstrate greater than 90% purity as determined by SDS-PAGE analysis .

How conserved is the CCR5 gene sequence across primates, and what does this tell us about its evolutionary history?

CCR5 sequences across primates exhibit high homology, indicating strong evolutionary conservation. Nucleotide and amino acid sequences are remarkably similar, with variations primarily concentrated at the amino and carboxyl termini. This conservation suggests critical functional importance throughout primate evolution .

The evolutionary rate analysis of CCR5 indicates a slowdown in primates after their divergence from rodents. The synonymous mutation rate in primates has remained relatively constant at approximately 1.1 × 10^-9 synonymous mutations per site per year. Comparative analyses of non-synonymous (Ka) and synonymous (Ks) substitution rates suggest that CCR5 genes have undergone negative or purifying selection, further emphasizing its functional importance .

Interestingly, Ka/Ks ratios differ significantly between cercopithecines and colobines, indicating that selective pressures have played different roles in these two lineages. This suggests potential adaptation to different pathogen pressures throughout evolutionary history .

What insights can Pongo abelii CCR5 provide about viral co-receptor function across primate species?

Pongo abelii CCR5, like other nonhuman primate CCR5 proteins, contains the critical Asp13 residue that facilitates CD4-independent binding of SIV gp120. This conservation across multiple primate species suggests that nonhuman primate CCR5 proteins, including Pongo abelii CCR5, might bind SIV gp120 without requiring CD4 presence .

This finding has significant implications for understanding viral entry mechanisms and host-virus co-evolution across primate species. Researchers can use recombinant Pongo abelii CCR5 to:

• Compare binding affinities with various viral envelope proteins

• Identify conserved and divergent interaction mechanisms

• Investigate the evolution of viral resistance strategies

• Develop comparative models for human viral interactions

Such studies contribute to our understanding of zoonotic transmission potential and the evolution of viral resistance mechanisms in different primate lineages .

How can recombinant Pongo abelii CCR5 be used in viral binding and entry studies?

Recombinant Pongo abelii CCR5 provides a valuable tool for comparative studies of viral binding and entry mechanisms. Researchers can employ the following methodologies:

• Cell-based assays: Transfect cells with recombinant Pongo abelii CCR5 expression vectors to assess viral entry efficiency compared to human CCR5

• Binding kinetics studies: Use surface plasmon resonance (SPR) with purified recombinant CCR5 to measure binding affinities with viral envelope proteins

• Competitive inhibition assays: Employ recombinant protein to screen potential inhibitors of viral entry

• Mutagenesis experiments: Generate site-specific mutations to identify critical residues for viral interactions

The presence of Asp13 in Pongo abelii CCR5, which is critical for CD4-independent binding of SIV gp120, makes this protein particularly useful for studying viral binding mechanisms that may differ from human CCR5-dependent interactions .

What structural modeling approaches provide the most accurate representation of Pongo abelii CCR5?

Homology modeling combined with molecular dynamics simulations offers the most comprehensive structural understanding of Pongo abelii CCR5. A robust methodology includes:

• Initial homology modeling: Using multiple template structures (such as PDB files 5UIW, 5T1A, 5LWE, and 4RWS) to create a merged structure

• Energy minimization: Optimizing the structure with pH-based pKa settings within a phosphatidyl-ethanolamine (PEA) lipid membrane

• Molecular dynamics simulation: Running simulations with explicit water molecules and appropriate ions (e.g., Cl and Na) for 300+ nanoseconds using established force fields such as AMBER14

• Trajectory analysis: Analyzing root-mean-squared deviation (RMSD) and root-mean-square fluctuation (RMSF) to understand protein stability and flexibility

• Dynamic cross-correlation matrix (DCCM) calculations: Identifying correlated movements between amino acids (using correlation cutoffs >0.9)

These simulations reveal that the seven transmembrane helices maintain stable structures with low RMSF values (<4Å), while the N- and C-termini exhibit greater flexibility (RMSF >10Å). Approximately 70% of amino acids show correlated movements with at least one other amino acid, highlighting the dynamic nature of the protein structure .

How do naturally occurring variants of Pongo abelii CCR5 affect function, and what are their implications for comparative studies?

Naturally occurring variants of Pongo abelii CCR5 can provide valuable insights into functional diversity and evolutionary adaptation. Analysis of these variants requires:

• Extraction of missense and loss-of-function variants from genomic databases

• Functional prediction using multiple tools (e.g., PolyPhen2, Provean, SIFT, Align-GVGD)

• Calculation of variant impact scores that integrate prediction scores with conservation data

• Correlation of variants with phenotypic data when available

While specific data on Pongo abelii CCR5 variants is limited, the methodology used for human CCR5 variant analysis can be applied. In humans, the CCR5-delta32 variant (a 32-base pair deletion) confers HIV resistance, highlighting the potential functional significance of structural variations in this receptor .

Comparative studies between human and Pongo abelii CCR5 variants can reveal shared mechanisms of adaptation and species-specific functional divergence. These insights contribute to our understanding of host-pathogen co-evolution across primate lineages.

What are the most effective strategies for analyzing CCR5 expression patterns in Pongo abelii tissues?

Understanding CCR5 expression patterns in Pongo abelii tissues requires multiple complementary approaches:

• Single-cell RNA sequencing: This technique allows for cell-type-specific expression profiling. Based on human and other primate data, CCR5 expression is expected in T-cells in blood and macrophages in peripheral tissues, including microglia in the brain .

• Quantitative PCR (qPCR): For relative quantification of CCR5 mRNA across different tissues.

• Immunohistochemistry/Immunofluorescence: Using validated antibodies that cross-react with Pongo abelii CCR5 to visualize protein expression in tissue sections.

• Flow cytometry: For quantifying CCR5 expression in isolated immune cell populations.

The expression profile in humans and other primates suggests CCR5 would be expressed in various macrophage and monocyte populations from liver, vessels, lung, and heart, as well as in microglia throughout the brain. This expression pattern reflects the diverse functional roles of CCR5 beyond viral reception .

How can structural differences between human and Pongo abelii CCR5 inform drug development strategies?

• Comparative homology modeling: Generating structural models of both human and Pongo abelii CCR5 using the same templates and protocols

• Binding site analysis: Identifying conserved and divergent features in potential drug binding pockets

• Molecular docking studies: Using in silico docking to predict how existing CCR5 antagonists might interact with Pongo abelii CCR5

• Molecular dynamics simulations: Assessing the stability and dynamics of drug-receptor complexes for both species

These comparative approaches can help identify:

• Conserved binding sites that might be targeted for broad-spectrum inhibitors

• Species-specific structural features that could lead to differential drug responses

• Novel binding pockets unique to each species that might be exploited for selective targeting

The high sequence homology suggests many existing human CCR5-targeting compounds may interact similarly with Pongo abelii CCR5, but subtle structural differences could impact binding affinities and kinetics. These insights can inform the design of more effective and potentially species-specific therapeutic agents .

What are the common challenges in recombinant Pongo abelii CCR5 expression and how can they be addressed?

Researchers working with recombinant Pongo abelii CCR5 may encounter several technical challenges that can be addressed through optimized protocols:

When working with the recombinant protein, reconstitution in deionized sterile water to 0.1-1.0 mg/mL and addition of glycerol (final concentration 5-50%) are recommended for optimal stability. Storage at -20°C/-80°C in small aliquots helps maintain protein integrity by preventing repeated freeze-thaw cycles .

How can researchers validate the functional activity of purified recombinant Pongo abelii CCR5?

Functional validation of recombinant Pongo abelii CCR5 is critical for ensuring experimental reliability. Several complementary approaches are recommended:

• Ligand binding assays: Using fluorescently labeled chemokines known to bind CCR5 to assess binding affinity and specificity

• Surface plasmon resonance (SPR): Measuring binding kinetics with natural ligands and viral envelope proteins

• Cell-based functional assays: Reconstituting the purified protein into liposomes or nanodisc systems to test receptor activation

• Structural integrity assessment: Using circular dichroism (CD) spectroscopy to confirm proper secondary structure formation

• Thermal stability analysis: Employing differential scanning fluorimetry to assess protein stability under various conditions

Comparing the functional properties of recombinant Pongo abelii CCR5 with those of human CCR5 can provide valuable insights into conserved mechanisms and species-specific differences. The presence of the critical Asp13 residue suggests that Pongo abelii CCR5 should retain binding capability for SIV gp120, which can serve as a positive control in functional validation experiments .