Recombinant Rat CD166 antigen (Alcam)

What is Rat CD166/ALCAM and what are its key structural features?

Rat ALCAM (Activated Leukocyte Cell Adhesion Molecule)/CD166 is a type I transmembrane cell adhesion molecule belonging to the immunoglobulin superfamily. Its extracellular domain contains five Ig-like domains - specifically three Ig-like C2-type domains and two Ig-like V-type domains. The amino-terminal V1 domain plays an essential role in ligand binding and ALCAM-mediated cell aggregation. Rat ALCAM has a protein sequence spanning from Met1-Lys527 with accession number O35112 . The molecular weight of the native protein is approximately 57.5 kDa, though after post-translational modifications it typically appears at 68-91 kDa in apparent molecular mass . The protein's structure enables both heterophilic (ALCAM-CD6) and homophilic (ALCAM-ALCAM) cell-cell interactions, making it a versatile mediator of cellular adhesion processes .

What are the primary cellular functions of Rat CD166/ALCAM?

Rat CD166/ALCAM functions as a crucial cell adhesion molecule involved in multiple biological processes. It serves as a ligand for CD6 expressed on T lymphocytes, mediating important immune cell interactions. The ALCAM/CD6 interaction plays significant roles in T cell development and regulation, as well as in the binding of T- and B-cells to activated leukocytes . Homophilic (ALCAM-ALCAM) adhesion has been demonstrated to facilitate tight cell-to-cell interaction and regulate stem cell differentiation . The protein is also involved in neurite extension by neurons through both heterophilic and homophilic interactions . While expressed across various tissues, ALCAM is typically restricted to subsets of cells engaged in dynamic growth and/or migration processes, highlighting its importance in neural development, branching organ development, hematopoiesis, immune response, and tumor progression .

How does Rat CD166/ALCAM compare to human and mouse orthologs?

Rat CD166/ALCAM shares significant structural and functional homology with its human and mouse counterparts. This conservation is particularly evident in the binding interface between CD166 and its receptor CD6. Studies have demonstrated that human CD166 binds to human, mouse, and rat CD6 with comparable affinity, indicating conservation of critical binding residues across species . The high degree of amino acid conservation in the binding face between human, mouse, and rat CD6 sequences suggests evolutionary preservation of this important interaction . When conducting cross-species experiments, researchers can exploit this conservation, as antibodies raised against human or mouse ALCAM often cross-react with rat ALCAM. For example, the antibody described in search result recognizes human, mouse, rat, and canine ALCAM/CD166, making it versatile for comparative studies .

What methods are recommended for detecting Rat CD166/ALCAM in tissue samples?

For detecting rat CD166/ALCAM in tissue samples, several validated methods have demonstrated reliable results:

Western Blot: Rat CD166/ALCAM can be detected in tissue lysates using polyclonal antibodies such as the Anti-Mouse/Rat/Canine ALCAM/CD166 Antibody. It typically appears as a band of approximately 90-120 kDa under reducing conditions . For optimal results, use PVDF membranes and Immunoblot Buffer Group 1 as demonstrated in previous studies .

Flow Cytometry: This technique is effective for detecting CD166/ALCAM on cell surfaces, particularly in immune cells. Studies have successfully identified ALCAM/CD166 expression in both resting and activated rat splenocytes . For flow cytometry applications, a dilution range of 1:20-100 is recommended when using conjugated antibodies .

Immunofluorescence/Immunohistochemistry: CD166/ALCAM can be visualized in rat tissues using immunofluorescence techniques. It has been successfully detected in rat mesenchymal stem cells using antibodies at a concentration of 10 μg/mL, with specific staining localized to the cytoplasm . For frozen tissue sections, a concentration of approximately 1.7 μg/mL with overnight incubation at 4°C has yielded optimal results . For immunocytochemistry applications, a dilution range of 1:50-200 is typically recommended .

What are the optimal storage and handling conditions for recombinant Rat CD166/ALCAM?

Proper storage and handling of recombinant Rat CD166/ALCAM is crucial for maintaining protein activity and stability. Lyophilized protein should be stored at -20 to -70°C and can remain stable for up to 12 months from the date of receipt . After reconstitution in sterile PBS (pH 7.4), the protein can be stored at 2-8°C for approximately one month . For longer-term storage post-reconstitution, aliquot the protein into multiple vials to avoid repeated freeze-thaw cycles and store at -20 to -70°C, where it can remain stable for up to 6 months .

When working with antibodies against CD166, store them at -20°C in aqueous buffered solutions containing 0.01M TBS (pH 7.4) with 1% BSA, 0.02% Proclin300, and 50% Glycerol . It is strongly recommended to aliquot antibodies into multiple vials to prevent protein degradation from repeated freeze-thaw cycles . Always handle the protein on ice when thawed and use aseptic techniques to prevent contamination.

How can researchers evaluate the binding activity of recombinant Rat CD166/ALCAM?

Evaluating the binding activity of recombinant Rat CD166/ALCAM can be accomplished through several methodological approaches:

Surface Plasmon Resonance (SPR): This technique provides quantitative binding kinetics for protein-protein interactions. Researchers have successfully immobilized rat ALCAM-His at 10 μg/ml (100 μl/well) to measure binding to mouse CD6-Fc, with EC50 values typically ranging between 0.08-0.18 μg/ml . SPR has also been used to quantify binding of soluble recombinant CD166 to different forms of streptavidin-immobilized chimeric CD6 .

Binding Assays with Mutagenesis Studies: To identify critical residues involved in CD166-CD6 interactions, mutagenesis studies can be conducted. Previous research mapped binding sites on CD6 and CD166 through extensive mutagenesis of CD6 domain 3 and CD166 domain 1 . These studies confirmed that CD6 domain 3 and CD166 domain 1 are sufficient to mediate binding .

Cross-Species Binding Analysis: Given that human CD166 binds human, mouse, and rat CD6 with similar affinity, cross-species binding assays can be utilized to assess functional activity . This approach can help validate the proper folding and functionality of recombinant proteins.

When performing these assays, it's essential to include appropriate controls to ensure specificity of the observed interactions and to account for potential background binding.

How can Rat CD166/ALCAM be utilized in studying T-cell development and immune regulation?

Rat CD166/ALCAM serves as a valuable tool for investigating T-cell development and immune regulation through several methodological approaches:

T-cell Activation Studies: Recombinant rat CD166/ALCAM can be immobilized on plates or beads to study its role in T-cell activation upon binding to CD6. Flow cytometry analysis of activated versus resting splenocytes has demonstrated differential expression patterns of ALCAM/CD166, suggesting its regulation during immune cell activation . Research has shown that ALCAM/CD6 interaction plays critical roles in T cell development and regulation, making this system suitable for studying these processes .

Co-culture Systems: Researchers can establish co-culture systems with cells expressing rat CD166/ALCAM and T-cells expressing CD6 to investigate heterophilic interactions in a controlled environment. These systems allow for the examination of signaling pathways activated upon ALCAM-CD6 binding.

Blocking Antibody Studies: Using antibodies that specifically block the ALCAM-CD6 interaction enables researchers to examine the functional consequences of disrupting this pathway in immune responses. The available antibodies that cross-react with rat ALCAM/CD166 (such as those described in and ) can be utilized in these studies.

Mutational Analysis: Based on the structural insights and binding data available for CD166-CD6 interactions , targeted mutations can be introduced to rat CD166/ALCAM to disrupt specific aspects of its binding to CD6, allowing for detailed functional analysis of different binding epitopes.

What approaches are effective for studying the role of Rat CD166/ALCAM in neural development?

Investigating rat CD166/ALCAM's role in neural development requires specialized methodological approaches:

Neurite Outgrowth Assays: Since ALCAM is involved in neurite extension by neurons via both heterophilic and homophilic interactions , researchers can coat surfaces with recombinant rat CD166/ALCAM to assess its impact on neurite outgrowth in primary rat neuronal cultures. Quantification of neurite length, branching, and growth cone dynamics provides insights into ALCAM's neuronal functions.

Ex Vivo Brain Slice Cultures: Rat brain slice cultures, particularly from cerebellum tissue where ALCAM expression has been documented , offer a system that maintains the cellular architecture while allowing experimental manipulation. Immunofluorescence staining using antibodies against ALCAM/CD166 at concentrations of approximately 1.7 μg/mL can visualize expression patterns in these cultures .

Neurosphere Assays: Since ALCAM is expressed in neural stem cells and may regulate their differentiation, neurosphere assays with rat neural stem cells can be used to investigate how ALCAM impacts proliferation, self-renewal, and differentiation capacity.

Function-Blocking Studies: Application of function-blocking antibodies against rat CD166/ALCAM in developing neural systems can reveal its necessity for specific developmental processes. Combined with time-lapse imaging, this approach can provide dynamic information about ALCAM's role during neural development.

How can researchers distinguish between homophilic and heterophilic interactions of Rat CD166/ALCAM?

Distinguishing between homophilic (ALCAM-ALCAM) and heterophilic (ALCAM-CD6) interactions presents a methodological challenge that can be addressed through several experimental strategies:

Competitive Binding Assays: Researchers can use recombinant rat CD6 to compete with ALCAM-ALCAM interactions, or recombinant rat ALCAM to compete with ALCAM-CD6 binding. Surface plasmon resonance (SPR) techniques used in previous studies can quantitatively assess these competitive effects.

Domain-Specific Mutations: Based on structural studies of CD166 and CD6, strategic mutations can be introduced to selectively disrupt either homophilic or heterophilic interactions. Previous mutagenesis data has identified residues in CD166 domain 1 critical for CD6 binding, particularly on the AGFCC′C′′ face . Creating mutants that specifically disrupt one type of interaction while preserving the other allows for dissection of their distinct functional roles.

Cell-Based Segregation Assays: Using cell lines expressing only rat ALCAM or only rat CD6, researchers can establish mixed culture systems and observe cell segregation patterns. Cells engaging in homophilic interactions will cluster together, while those forming heterophilic interactions will generate mixed clusters.

Single-Molecule Imaging: Advanced microscopy techniques like Förster resonance energy transfer (FRET) or fluorescence correlation spectroscopy can monitor ALCAM-ALCAM and ALCAM-CD6 interactions at the molecular level, providing spatial and temporal information about these distinct binding events.

What are the methodological considerations for using Recombinant Rat CD166/ALCAM in stem cell research?

Rat CD166/ALCAM has demonstrated importance in stem cell biology, particularly in mesenchymal stem cells where its expression has been documented . When utilizing recombinant rat CD166/ALCAM in stem cell research, several methodological considerations should be addressed:

Expression Analysis in Different Stem Cell Populations: Flow cytometry using antibodies against rat CD166/ALCAM can characterize expression levels across various stem cell populations and differentiation stages. This approach helps establish ALCAM as a potential marker for specific stem cell populations.

Functional Studies Using Recombinant Protein: Coating culture surfaces with recombinant rat CD166/ALCAM can modulate stem cell adhesion, proliferation, and differentiation processes. This approach helps delineate ALCAM's role in stem cell niche interactions.

Knockdown/Knockout Studies: RNA interference or CRISPR-Cas9 approaches targeting ALCAM in rat stem cells, combined with rescue experiments using recombinant protein, can establish causality between ALCAM expression and stem cell behaviors.

Co-culture Systems with Heterogeneous Cell Populations: Since ALCAM mediates both homophilic and heterophilic interactions, co-culture systems containing different cell types can elucidate how these interactions influence stem cell fate decisions in complex microenvironments.

When designing these experiments, researchers should consider that homophilic ALCAM-ALCAM adhesion has been shown to play important roles in tight cell-to-cell interaction and regulation of stem cell differentiation , suggesting it may be particularly relevant in stem cell niche biology.

What are common challenges when working with Recombinant Rat CD166/ALCAM and how can they be addressed?

Researchers working with recombinant rat CD166/ALCAM may encounter several technical challenges:

Protein Aggregation: As a cell adhesion molecule with homophilic binding capacity, ALCAM may form aggregates during storage or experimental procedures. To minimize this issue, maintain the protein in buffers containing low concentrations of detergents (0.01-0.05% Tween-20) and avoid excessive freeze-thaw cycles by storing as single-use aliquots .

Inconsistent Binding Activity: Variability in binding assays may occur due to protein degradation or improper folding. Always confirm protein activity using established binding assays, such as those measuring interaction with mouse CD6-Fc. The EC50 of mouse CD6-Fc binding to immobilized rat ALCAM-His should be approximately 0.08-0.18 μg/ml when the protein is fully active .

Detection Challenges in Complex Samples: When detecting native rat CD166/ALCAM in tissue samples, background signals or cross-reactivity may complicate interpretation. Optimize antibody concentrations for each application (1:300-5000 for Western blot, 1:20-100 for flow cytometry, and 1:50-200 for immunocytochemistry) and include appropriate negative controls.

Expression Variability Across Different Cell Types: ALCAM expression levels can vary significantly across different tissues and cellular activation states . When comparing expression between experimental conditions, normalize to appropriate housekeeping proteins and include positive control samples with known ALCAM expression.