CBP4 Antibody

What is CBX4 and what cellular functions does it perform?

CBX4, also known as E3 SUMO-protein ligase CBX4 or Polycomb 2 homolog, is a 560 amino acid protein containing one chromo domain. It functions as a transcriptional co-repressor involved in maintaining the transcriptionally repressive state of genes by modifying chromatin, rendering it heritably changed in its expressibility. CBX4 facilitates SUMO1 conjugation by UBE2I and is primarily localized in the nucleus. It is widely expressed in various tissues and plays important roles in gene silencing mechanisms .

What is the molecular weight discrepancy observed with CBX4 antibodies?

While the calculated molecular weight of CBX4 is 61 kDa based on its amino acid sequence, the observed molecular weight in experimental conditions is typically ~75 kDa. This discrepancy is attributed to post-translational modifications of the protein. When validating CBX4 antibody specificity, researchers should expect to observe bands at approximately 75 kDa rather than at the theoretical 61 kDa position in Western blot applications .

What cell and tissue types show CBX4 expression that can be detected with CBX4 antibodies?

CBX4 expression has been successfully detected using validated antibodies in various human cell lines including HEK-293 cells, PC-3 cells, and HeLa cells. The antibody also demonstrates reactivity with mouse and rat samples, making it suitable for comparative studies across these species. For immunofluorescence applications, positive detection has been specifically confirmed in HeLa cells .

What are the recommended applications and dilutions for CBX4 antibody?

The CBX4 antibody (18544-1-AP) has been validated for multiple applications with specific optimized dilutions:

For optimal results, researchers should titrate the antibody in each specific testing system as detection sensitivity may vary depending on sample preparation and experimental conditions .

How should sample preparation differ when using CBX4 antibody for nuclear protein detection?

Since CBX4 is primarily localized in the nucleus, special considerations for nuclear protein extraction are essential. For Western blot applications, researchers should employ nuclear extraction protocols that include appropriate detergents and salt concentrations to effectively solubilize nuclear proteins. When performing immunofluorescence, fixation and permeabilization methods significantly impact nuclear antigen accessibility. Paraformaldehyde fixation (4%) followed by Triton X-100 permeabilization (0.1-0.5%) has been validated for effective CBX4 detection. Additionally, antigen retrieval methods may be necessary for certain fixed tissue samples to expose the epitope recognized by the antibody .

What controls should be implemented when using CBX4 antibody in experimental designs?

Rigorous experimental controls are critical for validating CBX4 antibody specificity. These should include:

• Positive controls: Use cell lines known to express CBX4 (HEK-293, PC-3, HeLa)

• Negative controls: Include primary antibody omission controls and isotype controls

• Knockdown/knockout validation: siRNA or CRISPR-mediated depletion of CBX4 to confirm antibody specificity

• Peptide competition assays: Pre-incubation with immunizing peptide to confirm epitope specificity

Published research has utilized knockdown validation approaches, which should be considered the gold standard for confirming antibody specificity in experimental systems .

How can researchers address non-specific binding issues with CBX4 antibody?

Non-specific binding is a common challenge when working with polyclonal antibodies like the CBX4 antibody. To minimize these issues:

• Optimize blocking conditions: Increase blocking time or concentration (5% BSA or milk in TBST)

• Adjust antibody dilution: Further dilute the antibody if background is high

• Include detergents: Add 0.1-0.3% Tween-20 in washing buffers to reduce non-specific interactions

• Perform longer/more washing steps: Increase washing duration and frequency

• Pre-adsorb the antibody: Incubate with non-target tissue lysates to remove cross-reactive antibodies

• Optimize incubation temperature: Consider 4°C overnight incubation instead of room temperature

Each experimental system may require specific optimization of these parameters to achieve clean, specific detection of CBX4 .

What are the critical storage considerations for maintaining CBX4 antibody reactivity?

The CBX4 antibody should be stored at -20°C to maintain its reactivity and specificity. The antibody is stable for one year after shipment when stored properly. The formulation contains PBS with 0.02% sodium azide and 50% glycerol at pH 7.3, which helps maintain stability. Aliquoting is generally unnecessary for -20°C storage, reducing the risk of contamination from repeated freeze-thaw cycles. Note that some formulations (20μl sizes) contain 0.1% BSA as a stabilizer. When removing the antibody from storage, allow it to equilibrate to room temperature before opening to prevent condensation which could lead to contamination .

How can CBX4 antibody be employed in chromatin immunoprecipitation (ChIP) studies?

While not explicitly listed among the validated applications in the provided data, CBX4 antibodies can potentially be adapted for ChIP studies given CBX4's role as a chromatin modifier. For ChIP optimization:

• Crosslinking parameters: Optimize formaldehyde concentration (1-2%) and time (10-15 minutes)

• Sonication conditions: Adjust to achieve chromatin fragments of 200-500bp

• Antibody amount: Typically 2-5μg per ChIP reaction

• Washing stringency: Optimize salt concentrations in washing buffers

• Elution conditions: Ensure complete recovery of immunoprecipitated chromatin

Researchers should validate the antibody for ChIP applications through pilot experiments comparing results with published CBX4 binding sites and including appropriate negative controls (IgG and non-target genomic regions) .

What are the considerations for using CBX4 antibody in multiplex immunofluorescence studies?

For researchers conducting multiplex immunofluorescence to study CBX4 alongside other proteins:

• Antibody compatibility: Ensure primary antibodies are from different host species to avoid cross-reactivity

• Sequential staining: Consider sequential rather than simultaneous application if antibodies are from the same species

• Spectral separation: Select fluorophores with minimal spectral overlap

• Signal amplification: For weak CBX4 signals, implement tyramide signal amplification

• Appropriate controls: Include single-stain controls to assess bleed-through

• Blocking optimization: Use species-specific blocking reagents based on the host species of secondary antibodies

These considerations ensure accurate colocalization analysis of CBX4 with other proteins of interest in complex tissue or cellular contexts .

How should researchers optimize CBX4 antibody-based proximity ligation assays (PLA)?

PLA is listed as a validated application for the CBX4 antibody, making it valuable for studying protein-protein interactions involving CBX4. For optimal PLA results:

• Fixation protocol: Test multiple fixation methods as they significantly impact epitope accessibility

• Proximity probe selection: Choose probes compatible with the host species of both antibodies

• Antibody validation: Confirm both antibodies independently detect their targets before PLA

• Incubation conditions: Optimize time and temperature for primary antibody binding

• Signal-to-noise ratio: Adjust washing stringency to reduce background signals

• Quantification methods: Employ appropriate image analysis tools for objective signal quantification

PLA can reveal direct interactions between CBX4 and potential binding partners, providing insights into its functional role in chromatin modification and transcriptional regulation .

How does post-translational modification affect CBX4 detection with antibodies?

The observed molecular weight discrepancy between calculated (61 kDa) and detected (~75 kDa) CBX4 indicates significant post-translational modifications (PTMs). These modifications may include SUMOylation, phosphorylation, or other covalent additions that affect protein size and potentially epitope accessibility. Researchers should consider:

• Multiple band patterns: Different PTM states may manifest as multiple bands in Western blots

• Tissue/cell-specific differences: PTM patterns may vary across different biological contexts

• Treatment effects: Experimental treatments may alter PTM status and thus detection patterns

• Denaturing conditions: Some PTMs may be sensitive to sample preparation methods

Understanding these variables is crucial for accurate interpretation of CBX4 antibody results across different experimental conditions .

What considerations apply when comparing CBX4 to other chromobox family proteins in research?

CBX4 belongs to the chromobox family of proteins, which includes multiple members with structural similarities. When designing experiments to specifically study CBX4:

• Sequence homology analysis: Verify the antibody targets regions with low homology to other CBX proteins

• Cross-reactivity testing: Validate specificity against recombinant CBX proteins

• Functional differentiation: Design experiments that distinguish CBX4's unique SUMO ligase activity

• Expression pattern comparison: Compare detection patterns with known tissue-specific expression profiles

• Knockout validation: Use CBX4-specific knockout models as definitive negative controls

These approaches help ensure that observed results are specifically attributable to CBX4 rather than other chromobox family members with potentially overlapping functions .

How can researchers correlate CBX4 detection with functional outcomes in epigenetic studies?

To establish meaningful connections between CBX4 detection and its functional roles in epigenetic regulation:

• Combine detection approaches: Correlate protein levels (Western blot) with localization patterns (IF)

• Integrate with genomic data: Pair CBX4 detection with ChIP-seq to identify genome-wide binding patterns

• Gene expression correlation: Link CBX4 binding to transcriptional outcomes using RNA-seq

• Perturbation studies: Examine changes in histone modifications following CBX4 depletion

• Interaction analyses: Use co-immunoprecipitation or PLA to identify functional protein complexes

• Developmental timing: Consider temporal dynamics of CBX4 expression during cellular differentiation

This multi-dimensional approach allows researchers to move beyond simple detection to establish mechanistic insights into CBX4's functional roles in chromatin modification and gene regulation .