Recombinant Mouse C-C chemokine receptor type 5 (Ccr5)

What is the molecular structure of mouse CCR5?

Mouse CCR5 belongs to the large family of seven transmembrane proteins coupled to G proteins. It shares structural similarities with other chemokine receptors expressed on lymphocytes and immune cells. The receptor contains an N-terminal extracellular domain critical for ligand binding, seven transmembrane helices that traverse the cell membrane, and intracellular loops that interact with G proteins for signal transduction. Molecular modeling studies have used homology modeling to predict mouse CCR5 structure, building upon known structures of similar G protein-coupled receptors. These models typically include energy minimization within phosphatidyl-ethanolamine lipid membranes to better represent the native environment of CCR5 . Three-dimensional models have been generated through molecular dynamic simulations using the AMBER14 force field and explicit water molecules to better understand receptor conformational dynamics.

What are the primary ligands for mouse CCR5?

Mouse CCR5 interacts primarily with several CC chemokines, including CCL5 (RANTES), CCL3 (MIP-1α), and CCL4 (MIP-1β). These chemokines bind to the extracellular domains of CCR5 with varying affinities, triggering signaling cascades that regulate immune cell recruitment and function. Among these, CCL5 demonstrates high binding affinity and functional significance in mouse models. Research has shown that CCL5 interactions with CCR5 play crucial roles in inflammatory processes, including T-cell and macrophage migration. In vitro chemotaxis assays have demonstrated that exposure to 100 ng/ml recombinant mouse CCL5 results in significant increases in chemotaxis for both CD4+ and CD8+ T cells, as well as thioglycolate-elicited macrophages, confirming the functional importance of this receptor-ligand interaction .

What are the most effective methods for detecting mouse CCR5 expression?

Detection of mouse CCR5 requires sensitive methods due to its generally low expression levels under normal physiological conditions. Researchers should consider multiple complementary approaches:

• RT-PCR: This method allows for sensitive detection of CCR5 mRNA transcripts. Quantitative RT-PCR is particularly valuable for comparing expression levels across different tissues or conditions.

• Immunohistochemistry: Using specific antibodies against mouse CCR5, such as purified F(ab')2 fragments directed against the NH2-terminus of muCCR5, allows visualization of protein expression in tissue sections. This approach has been successfully used to detect CCR5 expression in delayed-type hypersensitivity reactions .

• Flow cytometry: For cellular expression analysis, flow cytometry using fluorescently labeled antibodies provides quantitative data on CCR5 surface expression at the single-cell level.

• Western blotting: For protein-level detection in tissue or cell lysates, though sensitivity may be limited compared to other methods.

When designing experiments, it's critical to include appropriate positive controls, such as activated T cells or macrophages, as CCR5 expression in mice is typically low in resting conditions and upregulated during immune activation .

How should researchers approach experimental models for studying mouse CCR5 function?

Selecting appropriate experimental models is crucial for meaningful CCR5 functional studies:

When designing experiments, researchers should consider that mouse CCR5 expression varies significantly based on immune activation state. For instance, models of delayed-type hypersensitivity show detectable CCR5 expression on macrophages, while certain inflammatory models like P. acnes-induced hepatitis do not induce significant CCR5 expression . This suggests that CCR5 may be preferentially involved in certain types of immune responses, particularly those mediated by cellular immunity rather than acute inflammatory processes. Creating appropriate positive and negative controls is essential for accurately interpreting results from these models.

What are the critical controls needed in mouse CCR5 functional studies?

Establishing proper controls is essential for valid interpretation of CCR5 functional studies:

• Expression controls: Include tissues or cells known to express CCR5 (activated T cells, macrophages) and those known not to express it.

• Antibody specificity controls: For immunological detection methods, include isotype controls and blocking peptides to verify antibody specificity.

• Functional assay controls: For chemotaxis studies, include positive controls (cells responding to known chemoattractants) and negative controls (medium without chemokines).

• Receptor antagonist controls: Use CCR5 antagonists or blocking antibodies to confirm that observed effects are specifically mediated through CCR5.

• Genetic controls: When possible, include CCR5-deficient cells or tissues as negative controls.

In chemotaxis assays evaluating CCR5 function, treatment with anti-CCL5 monoclonal antibodies has been shown to significantly reduce (p ≤ 0.01) the migration capability of both T cells and macrophages in response to recombinant CCL5, demonstrating the specificity of the receptor-ligand interaction . Such antibody-based inhibition provides an excellent control method to confirm that observed migration is genuinely CCR5-dependent.

What are the optimal expression systems for producing recombinant mouse CCR5?

Producing functional recombinant mouse CCR5 presents significant challenges due to its nature as a membrane protein with multiple transmembrane domains. Several expression systems can be employed, each with specific advantages:

• E. coli-based systems: While challenging for full-length CCR5, bacterial systems have been successfully used to express N-terminal fragments of mouse CCR5 fused to GST tags. This approach was demonstrated in studies where the 5' terminal extracellular binding domain (38 amino acids) of mouse CCR5 was expressed as a GST fusion protein for antibody production .

• Mammalian expression systems: HEK293 or CHO cells provide more native post-translational modifications and proper folding, crucial for functional studies of the receptor.

• Insect cell systems: Baculovirus-infected Sf9 or High Five cells offer a compromise between yield and post-translational modifications.

• Cell-free systems: Emerging approaches for membrane proteins that can allow controlled incorporation into nanodiscs or liposomes.

For functional studies, mammalian expression systems generally yield the most physiologically relevant recombinant CCR5, though at lower quantities than microbial systems. The choice of expression system should be guided by the specific experimental requirements, balancing protein yield with functional integrity.

What purification strategies yield the highest quality recombinant mouse CCR5?

Purification of membrane proteins like CCR5 requires specialized approaches:

• Detergent solubilization optimization: Screening multiple detergents (DDM, LMNG, CHS combinations) to identify conditions that maintain CCR5 stability.

• Affinity chromatography: Utilizing tags (His, FLAG) or ligand-based affinity methods for initial capture.

• Size exclusion chromatography: Critical for removing aggregates and ensuring monodispersity.

• Reconstitution into membrane mimetics: Incorporation into nanodiscs, liposomes, or other membrane mimetics to maintain native-like environment.

Quality assessment should include functional binding assays to confirm that purified CCR5 retains ligand-binding capability. For structural studies, additional considerations include protein stability and homogeneity, often assessed through techniques like thermal shift assays and analytical ultracentrifugation. When developing purification protocols, researchers should continuously monitor receptor conformation and ligand binding capacity to ensure the biological relevance of the purified protein.

How can researchers verify the functionality of recombinant mouse CCR5?

Verification of recombinant CCR5 functionality requires multiple complementary approaches:

• Ligand binding assays: Using labeled chemokines (particularly CCL5/RANTES) to confirm binding capacity through techniques like surface plasmon resonance or fluorescence-based binding assays.

• Signaling assays: Measuring calcium flux, GTPγS binding, or downstream pathway activation (MAPK, Akt) in response to ligand stimulation.

• Chemotaxis assays: Confirming the ability of the recombinant receptor to induce cell migration when expressed in appropriate cell types.

• Antibody recognition: Using conformationally-sensitive antibodies to verify proper folding.

Studies have demonstrated that functional CCR5 should respond to CCL5 stimulation by inducing chemotaxis in appropriate cellular contexts. In research using virus-specific T cells, exposure to 100 ng/ml recombinant mouse CCL5 resulted in significant increases in chemotaxis for both CD4+ and CD8+ T cells, an effect that could be blocked by pre-incubation with anti-CCL5 monoclonal antibodies . This type of functional assessment provides strong evidence for proper receptor activity.

How does mouse CCR5 contribute to viral infection models?

Mouse CCR5 plays significant roles in viral infection models, particularly in neuroinflammatory conditions:

• Coronavirus models: In mouse hepatitis virus (MHV) infection models, CCR5 and its ligands (particularly CCL5) contribute to both host defense and disease pathology. During viral encephalomyelitis, CCR5 mediates the recruitment of T cells and macrophages into the CNS, which is essential for viral clearance but also contributes to demyelination .

• Chemokine signaling: CCL5 (RANTES) binds to CCR5 and promotes migration of virus-specific T cells and macrophages. Neutralization of CCL5 using monoclonal antibodies has been shown to significantly reduce T cell and macrophage infiltration into the CNS of MHV-infected mice, confirming the importance of this receptor-ligand interaction in inflammatory cell recruitment .

• Differential effects on T cell subsets: Interestingly, antibody neutralization of CCL5 has been shown to differentially affect T cell subsets based on their antigen specificity. In MHV infection models, anti-CCL5 treatment resulted in a 73% reduction in virus-specific CD4+ T cells but only a 60% reduction in virus-specific CD8+ T cells, suggesting differential dependence on CCR5 signaling between T cell subsets .

These findings highlight the complex role of CCR5 in viral pathogenesis, where it contributes to both protective immunity and immunopathology, making it a potential therapeutic target for modulating disease outcomes.

What role does CCR5 play in autoimmune and inflammatory mouse models?

CCR5 exhibits distinct roles across different inflammatory and autoimmune conditions:

• Delayed-type hypersensitivity: Mouse CCR5 is upregulated in DTH reactions, suggesting its involvement in allergic processes mediated by cellular immunity. Immunohistochemical analysis has demonstrated positive CCR5 expression on macrophages in DTH models .

• Demyelinating diseases: In mouse models of viral-induced demyelination that mimic multiple sclerosis, CCR5 and its ligand CCL5 are localized in white matter tracts undergoing demyelination. Neutralization of CCL5 significantly reduces (p ≤ 0.005) the severity of demyelination and macrophage accumulation within the CNS, improving neurological function .

• Acute inflammatory conditions: Interestingly, CCR5 expression is not significantly upregulated in certain acute inflammatory conditions, such as P. acnes-induced fulminant hepatitis, suggesting specificity in its inflammatory roles .

• Neuroinflammation: CCR5 contributes to neuroinflammatory processes by facilitating T cell and macrophage entry into the CNS. Targeting the CCR5-CCL5 axis can reduce inflammation and improve outcomes in models of neuroinflammatory disease .

These varied roles underscore the context-dependent function of CCR5 in different immune-mediated pathologies, highlighting the importance of considering disease-specific mechanisms when targeting this receptor therapeutically.

How can mouse CCR5 research inform human therapeutic development?

Translating mouse CCR5 research to human applications requires careful consideration of several factors:

This translational approach allows mouse CCR5 research to serve as a foundation for human therapeutic strategies while acknowledging the limitations and necessary adaptations required for successful clinical application.

What molecular modeling approaches are most effective for studying mouse CCR5 structure-function relationships?

Advanced computational approaches provide valuable insights into CCR5 structure and function:

• Homology modeling: Utilizes known structures of related GPCRs to predict CCR5 conformation. Effective models merge multiple template structures (such as PDB files 5UIW, 5T1A, 5LWE, and 4RWS) to create comprehensive structural predictions .

• Molecular dynamics simulations: Simulations of CCR5 embedded in phosphatidyl-ethanolamine lipid membranes with explicit water molecules provide dynamic insights into receptor behavior. Using force fields like AMBER14 with simulations running for hundreds of nanoseconds reveals conformational changes relevant to ligand binding and signaling .

• Ligand docking studies: Computational docking of chemokines and small molecule antagonists helps predict binding modes and key interaction residues.

• Energy minimization approaches: Optimization of receptor structures using physics-based calculations at physiologically relevant pH (7.4) improves model accuracy .

These computational approaches complement experimental data and provide mechanistic hypotheses that can be tested experimentally. For educational and collaborative purposes, the resulting models can be converted to shareable formats and uploaded to repositories like FigShare or used to generate 3D-printed models for structural analysis .

What are the most sensitive approaches for measuring CCR5-ligand interactions?

Quantifying CCR5-ligand interactions requires sophisticated techniques that balance sensitivity with physiological relevance:

• Surface plasmon resonance (SPR): Provides real-time, label-free detection of binding kinetics and affinity constants between purified CCR5 (or CCR5-expressing membrane preparations) and chemokine ligands.

• Bioluminescence resonance energy transfer (BRET): Allows measurement of receptor-ligand interactions and subsequent conformational changes in living cells.

• Radioligand binding assays: Traditional approach using radiolabeled chemokines to determine binding parameters through saturation and competition studies.

• Functional readouts: Measurement of downstream signaling events such as calcium flux, β-arrestin recruitment, or inhibition of cAMP production provides functional confirmation of ligand engagement.

• Chemotaxis assays: Quantification of cell migration in response to CCR5 ligands provides a functional readout with high physiological relevance. Studies have demonstrated that exposure to recombinant mouse CCL5 at concentrations of 100 ng/ml induces significant chemotaxis in both T cells and macrophages, effects that can be blocked by anti-CCL5 antibodies .

Each approach offers distinct advantages, and combining multiple techniques provides the most comprehensive characterization of receptor-ligand interactions. The choice of method should be guided by the specific research question, with consideration of factors such as the need for quantitative binding parameters versus functional outcomes.

How can researchers effectively analyze CCR5 expression dynamics in complex tissues?

Analysis of CCR5 expression in heterogeneous tissues requires specialized approaches:

• Single-cell RNA sequencing: Provides cell-type specific expression data in complex tissues, revealing which populations express CCR5 under different conditions.

• Multiplexed immunofluorescence: Allows simultaneous detection of CCR5 alongside cell type markers and activation states in tissue sections.

• Flow cytometry and cell sorting: Enables quantitative analysis of CCR5 surface expression across different cell populations isolated from tissues.

• In situ hybridization techniques: Methods like RNAscope provide sensitive detection of CCR5 mRNA with spatial context in tissue sections.

• qRT-PCR with cell isolation: Combining cell sorting or laser capture microdissection with qRT-PCR allows quantitative expression analysis from specific cell populations.

Research has demonstrated that CCR5 expression is dynamically regulated in different disease contexts. For example, in models of viral-induced neuroinflammation, treatment with anti-CCL5 antibodies significantly reduced CCR5 mRNA expression in the CNS compared to control-treated animals, suggesting feedback regulation between ligand availability and receptor expression . This highlights the importance of analyzing expression dynamics rather than static expression levels.

What are the current knowledge gaps in mouse CCR5 biology?

Despite significant advances, several critical knowledge gaps remain in our understanding of mouse CCR5:

• Structure-function relationships: Detailed understanding of how specific structural elements of mouse CCR5 contribute to different signaling outcomes remains incomplete.

• Tissue-specific roles: The function of CCR5 in non-immune tissues and its contribution to normal physiological processes beyond inflammation requires further investigation.

• Developmental regulation: The role of CCR5 in developmental processes and how its expression is regulated throughout development is poorly understood.

• Signaling complexity: The complete signaling network downstream of CCR5 activation, including potential biased signaling in response to different ligands, needs further characterization.

• Genetic variation impact: The functional consequences of natural genetic variations in mouse CCR5 across different strains and how these might influence disease susceptibility require additional study.

Addressing these knowledge gaps will provide a more comprehensive understanding of CCR5 biology and potentially reveal new therapeutic opportunities. Future research should employ multidisciplinary approaches combining advanced genetic tools, high-resolution imaging, and systems biology to address these complex questions.

What emerging technologies will advance mouse CCR5 research?

The future of CCR5 research will be shaped by several cutting-edge technologies:

• CRISPR-based approaches: Advanced genome editing enables precise modification of CCR5 or its regulatory elements, facilitating detailed structure-function studies and development of improved mouse models.

• Cryo-EM and advanced structural biology: These techniques hold promise for determining high-resolution structures of CCR5 in complex with various ligands and signaling partners.

• Spatial transcriptomics and proteomics: These methods provide unprecedented insights into the expression and function of CCR5 within the spatial context of tissues.

• Optogenetic and chemogenetic tools: Allow temporal control of CCR5 signaling for dissecting its acute versus chronic roles in various physiological and pathological processes.

• Artificial intelligence approaches: Machine learning methods can integrate diverse datasets to predict CCR5 function in different contexts and guide experimental design.

By embracing these technologies, researchers can develop a more integrated understanding of CCR5 biology that spans from molecular mechanisms to physiological outcomes. This comprehensive approach will be essential for translating basic research findings into clinical applications.