Recombinant Semnopithecus entellus C-C chemokine receptor type 5 (CCR5)

What is Recombinant Semnopithecus entellus C-C Chemokine Receptor Type 5 (CCR5)?

Recombinant Semnopithecus entellus CCR5 is a laboratory-produced form of the natural CCR5 protein found in Hanuman langurs (also known as Presbytis entellus). It is a member of the beta chemokine receptor family and functions as a seven-transmembrane protein similar to G protein-coupled receptors . The full-length protein consists of 352 amino acids and has several alternative names including C-C CKR-5, CC-CKR-5, CCR-5, and CD195 . When produced recombinantly, the protein maintains the structural and functional characteristics of native CCR5 but can be tagged (often with histidine residues) to facilitate purification and detection in experimental settings.

How does Semnopithecus entellus CCR5 compare to human CCR5?

While both Semnopithecus entellus CCR5 and human CCR5 belong to the same family of G protein-coupled receptors and share significant sequence homology, they exhibit species-specific variations that may affect their function and interaction with ligands and pathogens. Human CCR5 is known to function as a co-receptor for HIV entry into cells and has been extensively studied in this context .

Comparative studies between human and non-human primate CCR5 variants help researchers understand evolutionary adaptations and resistance mechanisms to viral infections. In humans, a 32-bp deletion mutation (CCR5-Δ32) confers resistance to HIV-1 infection, demonstrating the critical role of specific regions in determining receptor function . Similar comparative analyses of Semnopithecus entellus CCR5 could provide insights into primate-specific adaptations and potential resistance mechanisms.

What are the recommended storage conditions for recombinant Semnopithecus entellus CCR5?

For optimal stability and activity, recombinant Semnopithecus entellus CCR5 should be stored at -20°C, and for extended storage, it is recommended to conserve it at -20°C or -80°C . The protein is typically supplied in a storage buffer containing Tris-based buffer with 50% glycerol, optimized for protein stability .

Importantly, repeated freezing and thawing should be avoided as this can lead to protein degradation and loss of activity. For short-term use, working aliquots can be stored at 4°C for up to one week . This approach minimizes the need for repeated freeze-thaw cycles of the main stock.

How does the oligomerization of CCR5 impact its function in experimental systems?

CCR5 demonstrates complex oligomerization behavior that significantly impacts its function and should be considered in experimental design. Wild-type CCR5 can polymerize not only with itself (homopolymerization) but also with its truncated delta-32 form and with other chemokine receptors such as CCR2 . Additionally, CCR5 can form heterodimers with other G protein-coupled receptors, including opioid receptors .

These oligomerization patterns may influence CCR5 conformation, ligand binding properties, and downstream signaling cascades. When designing experiments with recombinant Semnopithecus entellus CCR5, researchers should consider how the expression system and experimental conditions might affect receptor oligomerization and consequently alter functional outcomes. For instance, the presence of detergents, lipids, or co-expression of other membrane proteins can influence the oligomeric state of the receptor.

The significance of homo- and hetero-dimerization on CCR5 conformation, binding, and signaling remains an active area of research, with important implications for understanding receptor function in different cellular contexts .

What methodological approaches can be used to study Semnopithecus entellus CCR5 interactions with HIV envelope proteins?

Several methodological approaches can be employed to investigate the interactions between Semnopithecus entellus CCR5 and HIV envelope proteins:

• Surface Plasmon Resonance (SPR): This technique allows real-time measurement of binding kinetics between purified recombinant CCR5 and HIV envelope glycoproteins. The receptor can be immobilized on a sensor chip, and various concentrations of gp120 (alone or in complex with CD4) can be passed over the surface to determine association and dissociation rates.

• Cell-based Fusion Assays: These assays involve co-expression of CCR5 with CD4 in target cells and HIV envelope proteins in effector cells. Upon co-culture, cell fusion occurs if the receptor successfully interacts with the viral proteins, which can be quantified using reporter systems.

• Competitive Binding Assays: Using labeled chemokines (natural ligands of CCR5) and measuring displacement by HIV envelope proteins can provide insights into binding site overlap and competitive mechanisms.

• Structural Studies: Techniques such as X-ray crystallography, cryo-electron microscopy, or nuclear magnetic resonance can elucidate the molecular details of CCR5-HIV interactions, though these require highly purified and stable protein preparations.

When studying Semnopithecus entellus CCR5, comparing its interaction properties with those of human CCR5 can provide valuable insights into species-specific resistance or susceptibility to HIV infection .

How can recombinant Semnopithecus entellus CCR5 be used to study natural resistance to HIV?

Recombinant Semnopithecus entellus CCR5 offers a valuable tool for studying natural resistance mechanisms to HIV infection through several research approaches:

• Comparative Binding Studies: By comparing the binding affinity of HIV envelope proteins to recombinant CCR5 from Semnopithecus entellus versus human CCR5, researchers can identify species-specific differences that might confer resistance. This is particularly relevant as naturally occurring CCR5 mutations in humans have been associated with HIV resistance .

• Mutagenesis Analysis: Systematic site-directed mutagenesis of recombinant Semnopithecus entellus CCR5 can help identify specific amino acid residues critical for HIV binding. Comparing these to human CCR5 variants can reveal evolutionary adaptations that affect viral entry.

• Chimeric Receptor Studies: Creating chimeric receptors containing domains from both Semnopithecus entellus and human CCR5 can help map the regions responsible for differential HIV susceptibility between species.

• Cell-based Viral Entry Assays: Expressing recombinant Semnopithecus entellus CCR5 in cell lines that lack endogenous co-receptors allows for controlled studies of its ability to support HIV entry compared to human variants.

The identification of naturally occurring CCR5-specific antibodies in humans who remain uninfected despite HIV exposure suggests that natural autoimmunity to CCR5 may play a role in HIV control . Similar mechanisms could potentially exist in non-human primates and might be explored using recombinant Semnopithecus entellus CCR5.

What expression systems are most effective for producing functional recombinant Semnopithecus entellus CCR5?

The choice of expression system significantly impacts the yield, functionality, and post-translational modifications of recombinant Semnopithecus entellus CCR5. Several options with their respective advantages and limitations include:

For functional studies of CCR5-HIV interactions or signaling assays, mammalian expression systems are generally recommended despite their lower yield, as they ensure the receptor adopts its native conformation with appropriate post-translational modifications.

What purification strategies maximize both yield and functionality of recombinant Semnopithecus entellus CCR5?

Purifying membrane proteins like CCR5 while maintaining their native structure and function requires specialized approaches:

Recommended Purification Protocol:

• Membrane Preparation: Harvest cells expressing recombinant Semnopithecus entellus CCR5 and prepare membrane fractions through differential centrifugation to concentrate the receptor.

• Solubilization: Use mild detergents such as n-dodecyl-β-D-maltoside (DDM), lauryl maltose neopentyl glycol (LMNG), or digitonin that effectively extract the receptor while preserving its structure. A buffer containing a mixture of lipids can help maintain the native environment.

• Affinity Chromatography: Utilize affinity tags (His-tag is common for recombinant CCR5) for initial purification . For His-tagged CCR5, immobilized metal affinity chromatography (IMAC) with Ni-NTA resin is effective under optimized conditions.

• Size Exclusion Chromatography: This step helps separate monomeric from oligomeric CCR5 and removes aggregates. It also allows buffer exchange to reduce detergent concentration to just above critical micelle concentration.

• Functional Verification: Test binding of known chemokine ligands (MCP-2, MIP-1α, MIP-1β, or RANTES) to confirm that the purified receptor remains functional .

Throughout purification, maintaining a stable buffer composition (typically Tris-based with 50% glycerol) and working at 4°C helps preserve receptor functionality. The addition of cholesterol or specific lipids in the purification buffers can significantly improve stability and activity of the purified receptor.

What assays can reliably measure the functional activity of purified recombinant Semnopithecus entellus CCR5?

Several complementary assays can be employed to verify the functional integrity of purified recombinant Semnopithecus entellus CCR5:

• Ligand Binding Assays:

  • Radioligand binding using 125I-labeled chemokines

  • Fluorescence-based binding assays with labeled ligands

  • Surface plasmon resonance (SPR) to measure binding kinetics to natural ligands like MCP-2, MIP-1α, MIP-1β, and RANTES

• Conformational Integrity Assessment:

  • Circular dichroism (CD) spectroscopy to verify secondary structure content

  • Thermal stability assays using differential scanning fluorimetry

  • Limited proteolysis to assess proper folding

• Functional Reconstitution:

  • Incorporation into proteoliposomes followed by G protein activation assays

  • GTPγS binding assays to measure receptor-mediated G protein activation

  • Reconstitution in nanodiscs for structural and functional studies

• Cell-Based Functional Assays (if reincorporated into cell membranes):

  • Calcium flux assays upon ligand stimulation

  • β-arrestin recruitment assays

  • Chemotaxis assays to measure directional cell migration

For comparative assessment, parallel testing of human CCR5 can serve as a benchmark to evaluate the relative activity of the Semnopithecus entellus variant. When conducting these assays, it's important to consider that CCR5 can act not only as a chemokine receptor inducing cell chemotaxis but also as a costimulatory molecule in immune synapses .

How does the CCR5 sequence variation across primates inform evolutionary adaptation to viral pathogens?

The sequence variation of CCR5 across primate species provides valuable insights into evolutionary adaptation to viral pathogens:

Comparative analysis of these variations reveals distinct evolutionary pressures across primate lineages. The existence of the CCR5-Δ32 allele in human populations, with frequencies ranging from 16.4% in Norwegian populations to 0% in Ethiopian populations , suggests selective pressure potentially from historical pandemics. Similar to how CCR5-Δ32 confers HIV resistance in humans, variant analysis in Semnopithecus entellus and other non-human primates may reveal alternative evolutionary strategies for viral resistance.

The study of these variations contributes to our understanding of host-pathogen co-evolution and has significant implications for the development of antiviral strategies targeting CCR5 . By identifying conserved and variable regions across primate CCR5 sequences, researchers can better understand the molecular determinants of viral entry and species-specific susceptibility patterns.

What are the implications of CCR5 research for the development of HIV entry inhibitors?

Research on primate CCR5 variants, including Semnopithecus entellus CCR5, has substantial implications for HIV entry inhibitor development:

• Identification of Critical Binding Domains: Comparative studies of CCR5 across primate species help identify conserved domains essential for HIV binding. These regions represent potential targets for broad-spectrum entry inhibitors that might be less susceptible to viral escape mutations.

• Natural Resistance Models: The identification of naturally occurring CCR5-specific antibodies in exposed but uninfected individuals suggests that autoimmunity to CCR5 may contribute to HIV resistance . This observation has prompted strategies targeting CCR5 to achieve anti-HIV humoral responses.

• Receptor Antagonist Design: Understanding structural differences between human and non-human primate CCR5 can guide the development of small molecule antagonists that specifically block HIV interaction with CCR5 without disrupting normal chemokine signaling.

• Antibody-Based Approaches: Research on naturally occurring antibodies against CCR5 in both humans and non-human primates provides templates for developing therapeutic antibodies that block HIV entry while minimizing immunogenicity.

• Gene Therapy Strategies: The success of CCR5-Δ32 in conferring HIV resistance has inspired gene editing approaches targeting CCR5. The breakthrough in long-term HIV control through stem-cell transplantation from CCR5-Δ32 donors demonstrates the potential of CCR5-focused therapies .

By studying evolutionary adaptations in primate CCR5, researchers can identify natural solutions to viral resistance that may inspire novel therapeutic approaches with potentially fewer side effects than completely synthetic designs.

How can recombinant Semnopithecus entellus CCR5 contribute to understanding the molecular mechanisms of chemokine signaling?

Recombinant Semnopithecus entellus CCR5 offers unique opportunities to explore fundamental aspects of chemokine signaling:

• Comparative Signaling Studies: Differences in signaling outcomes between Semnopithecus entellus CCR5 and human CCR5 in response to the same chemokines (MCP-2, MIP-1α, MIP-1β, RANTES) can reveal species-specific adaptations in signal transduction pathways. This may provide insights into the evolution of immune responses.

• Structure-Function Analysis: By creating chimeric receptors or point mutations, researchers can map the specific domains and residues responsible for ligand recognition, G protein coupling, and β-arrestin recruitment. This information helps define the molecular determinants of signaling specificity.

• Receptor Oligomerization Effects: The ability of CCR5 to form homodimers and heterodimers with other receptors suggests complex regulation of signaling . Studying how oligomerization affects Semnopithecus entellus CCR5 signaling can reveal general principles of GPCR crosstalk.

• Receptor Compartmentalization: CCR5 function is influenced by its localization to lipid rafts through palmitoylated cysteine residues in its C-terminal domain . Comparative analysis of membrane distribution between primate CCR5 variants can reveal how subcellular localization impacts signaling.

• Beyond Chemotaxis: Research has shown that CCR5 functions not only in chemotaxis but also as a costimulatory molecule in immune synapses . Investigating these non-canonical roles in different primate species can broaden our understanding of CCR5's diverse functions in immunity.

These studies collectively contribute to a more comprehensive model of chemokine receptor signaling, potentially revealing novel therapeutic targets for inflammatory and immune disorders beyond HIV infection.