RAD51A Antibody

What is RAD51A and what is its role in DNA repair?

RAD51A (also known as RAD51) is a key recombinase protein involved in homologous recombination (HR), a fundamental DNA repair pathway that uses undamaged sister chromatids as templates to restore genetic information. This protein plays a critical role in homologous pairing and strand transfer of DNA during repair of double-strand breaks. RAD51 is a member of the RecA protein family, which also includes RecA, RadA, and Dmc1 . The protein functions by searching out and pairing homologous DNA sequences and then promoting strand exchange between them, which is vital for maintaining genomic integrity . RAD51's importance is highlighted by its interaction with tumor suppressor proteins BRCA1 and BRCA2, where BRCA2 regulates both the intracellular localization and DNA-binding ability of RAD51 .

What are the technical specifications of human RAD51A protein?

Human RAD51A protein has the following specifications:

• Amino acid length: 339 residues

• Molecular weight: 37 kDa

• Subcellular localization: Nucleus, mitochondria, and cytoplasm

• Isoforms: Up to 4 different isoforms

• Expression profile: Highly expressed in testis and thymus, followed by small intestine, placenta, colon, pancreas, and ovary

• Protein family: Member of the RecA protein family

• Known synonyms: FANCR, HRAD51, HsRad51, HsT16930, MRMV2, RAD51A, RECA, and BRCC5

RAD51 gene orthologs have been identified in various species including mouse, rat, bovine, frog, zebrafish, chimpanzee, and chicken, demonstrating its evolutionary conservation and biological importance .

What are the common applications for RAD51A antibodies in research?

RAD51A antibodies are versatile research tools with multiple applications:

Over 580 citations in the literature describe the use of RAD51 antibodies in research, with Western Blot being the most commonly employed technique . The choice of application depends on the specific research question and experimental design.

What sample preparation methods are optimal for RAD51A immunodetection?

For optimal RAD51A immunodetection, sample preparation methods should be tailored to the specific application:

For Western Blot analysis:

• Harvest cells during exponential growth phase

• Lyse cells in RIPA buffer supplemented with protease inhibitors

• Include phosphatase inhibitors if studying phosphorylated forms of RAD51

• Use nuclear extraction protocols for enriched detection, as RAD51 is predominantly nuclear

• For optimal separation, use 10-12% SDS-PAGE gels

• Transfer to PVDF membranes (preferred over nitrocellulose for this protein)

For Immunofluorescence:

• Fix cells with 4% paraformaldehyde (10-15 minutes at room temperature)

• Permeabilize with 0.2% Triton X-100

• Include a DNA damage inducing agent (e.g., ionizing radiation, hydroxyurea, or etoposide) to study RAD51 foci formation

• Counterstain with DAPI to visualize nuclei

• Use recommended antibody dilutions of 1-5 μg/ml

For Immunohistochemistry:

• Use formalin-fixed paraffin-embedded (FFPE) or frozen tissue sections

• For FFPE samples, perform antigen retrieval using citrate buffer (pH 6.0)

• Block endogenous peroxidase activity with hydrogen peroxide

• Include appropriate positive controls (testis tissue shows high RAD51 expression)

How do you validate the specificity of a RAD51A antibody for research use?

Validating RAD51A antibody specificity is crucial for ensuring reliable experimental results:

• Positive and negative controls:

  • Use cell lines with known RAD51 expression levels

  • Include RAD51 knockout/knockdown cells as negative controls

  • Use cells with induced DNA damage to upregulate RAD51 as positive controls

• Molecular weight verification:

  • Confirm detection of a band at approximately 37 kDa by Western Blot

  • Be aware of potential post-translationally modified forms

• Cross-reactivity assessment:

  • Test antibody against multiple species if conducting comparative studies

  • Verify specificity against other RAD51 paralogs (RAD51B, RAD51C, RAD51D)

• Immunodepletion studies:

  • Pre-incubate antibody with purified RAD51 protein

  • Confirm signal reduction in subsequent applications

• Functional validation:

  • Verify co-localization with γH2AX foci after DNA damage

  • Confirm nuclear localization pattern

  • Demonstrate interaction with known partners (e.g., BRCA2) via co-immunoprecipitation

• Multiple antibody comparison:

  • Use antibodies targeting different epitopes of RAD51

  • Compare staining patterns across techniques

How does RAD51 function mechanistically in homologous recombination?

The mechanistic function of RAD51 in homologous recombination involves several coordinated steps:

• Presynaptic filament formation:

  • RAD51 binds to single-stranded DNA (ssDNA) generated at DNA double-strand breaks

  • Forms a nucleoprotein filament in a process facilitated by mediator proteins

  • BRCA2 regulates RAD51's DNA-binding ability and intracellular localization

  • The filament forms a right-handed helical structure around ssDNA

• Homology search and strand invasion:

  • The RAD51-ssDNA filament searches for homologous sequences in double-stranded DNA

  • Recognition involves more than just hydrogen bond-directed base pair formation

  • Hydrophobic effects affecting stacking of nucleobases likely play a role in sequence recognition

  • The filament can recognize sequence identity over several bases with high accuracy

• Strand exchange:

  • Upon finding homology, RAD51 catalyzes the exchange of the invaded strand with its complementary strand

  • This creates a displacement loop (D-loop) structure

  • The process requires ATP hydrolysis for RAD51 function

• Post-synaptic events:

  • DNA polymerases extend the invading 3' end using the homologous template

  • Resolution of intermediates leads to error-free repair

Recent research suggests that "longitudinal breathing" (kinetic effects of DNA base stacking and unstacking) may be crucial for RAD51's ability to recognize sequence identity across long DNA stretches with high fidelity .

What experimental approaches can be used to assess RAD51 filament formation on DNA?

Several experimental approaches can assess RAD51 filament formation on DNA:

• Electron Microscopy (EM):

  • Provides direct visualization of RAD51-DNA filament structures

  • Can distinguish between active and inactive filament forms

  • Sample preparation involves fixation and staining or cryo-EM techniques

• Single-Molecule Techniques:

  • Fluorescence Resonance Energy Transfer (FRET) measures DNA extension during filament formation

  • DNA curtain assays visualize RAD51 binding along DNA in real-time

  • Magnetic tweezers measure mechanical properties of RAD51-coated DNA

• Biochemical Assays:

  • Electrophoretic mobility shift assays (EMSA) detect RAD51-DNA complex formation

  • DNA protection assays measure resistance to nucleases

  • ATP hydrolysis assays indirectly monitor filament assembly/disassembly kinetics

• Fluorescence-Based Approaches:

  • RAD51 foci formation after DNA damage (indirect measure of filament formation in cells)

  • Super-resolution microscopy techniques (STORM, PALM) for detailed visualization

  • Fluorescently labeled RAD51 for live-cell imaging

• Structural Studies:

  • X-ray crystallography and Cryo-EM for high-resolution structures

  • NMR spectroscopy for dynamics information

These approaches collectively provide insights into the formation, stability, and function of RAD51 filaments in both in vitro and cellular contexts.

How can RAD51 activity be inhibited in experimental settings?

RAD51 activity can be inhibited through several experimental approaches:

• Small Molecule Inhibitors:

  • Several compounds have been identified as potential inhibitors of RAD51 activity

  • These are being investigated for enhancing the efficacy of radio- and chemotherapies

  • Small molecules disrupt RAD51's DNA binding capacity or nucleofilament formation

• Antibody-Based Approaches:

  • Novel cell-penetrating antibody fragments can bind RAD51 with high affinity (KD = 8.1 nM)

  • These fragments inhibit RAD51 ssDNA binding in vitro

  • Cell-penetrating peptide "iPTD" fusion enables antibody fragments to enter living cells

• Genetic Approaches:

  • siRNA or shRNA-mediated knockdown of RAD51

  • CRISPR-Cas9 gene editing for RAD51 knockout

  • Expression of dominant-negative RAD51 mutants

• Indirect Inhibition:

  • Targeting RAD51 regulators like BRCA2 or RAD51 paralogs

  • Inhibiting post-translational modifications required for RAD51 activation

  • Disrupting RAD51 nuclear localization

Research has shown that inhibition or downregulation of RAD51 increases the efficiency of radiotherapy and chemotherapy in cancer contexts , making these approaches valuable for both fundamental research and potential therapeutic applications.

What is the relationship between RAD51 expression and cancer therapy resistance?

RAD51 plays a complex role in cancer therapy resistance:

• Protective Mechanism Against DNA-Damaging Therapies:

  • RAD51 repairs DNA damage induced by radio- and chemotherapies

  • Higher expression levels correlate with increased resistance to these treatments

  • Inhibition or downregulation enhances therapeutic efficacy

• RAD51 Overexpression in Cancers:

  • Multiple studies report RAD51 overexpression in various cancer types

  • Elevated expression correlates with reduced patient survival

  • Overexpression promotes cancer progression by increasing malignancy and metastatic potential

• Therapeutic Response Prediction:

  • RAD51 expression levels can potentially predict response to DNA-damaging therapies

  • Cancers with defects in HR (like BRCA-mutated tumors) are more sensitive to certain therapies

  • RAD51 foci formation can serve as a functional biomarker for HR proficiency

• Compensatory Mechanisms:

  • Many cancers have epigenetic deficiencies in DNA repair genes

  • RAD51 overexpression may compensate for these deficiencies

  • This adaptive response contributes to therapy resistance

RAD51 is considered a promising target for treatment of several cancers, including cervical carcinoma, breast cancer, and non-small-cell lung cancer . Understanding the relationship between RAD51 and therapy resistance is crucial for developing effective therapeutic strategies.

How do post-translational modifications affect RAD51 function?

Post-translational modifications (PTMs) of RAD51 serve as regulatory switches that fine-tune its activity:

These modifications regulate RAD51 at multiple levels:

• Spatiotemporal regulation: PTMs control when and where RAD51 is activated within the cell

• Protein stability: Modifications like ubiquitination regulate RAD51 protein levels

• Protein-protein interactions: PTMs can promote or inhibit interactions with binding partners

• DNA binding capacity: Modifications directly affect RAD51's ability to form nucleoprotein filaments

• Cell cycle dependency: Some modifications only occur during specific cell cycle phases

Experimental methods to study these modifications include site-directed mutagenesis, phospho-specific antibodies, mass spectrometry, and in vitro reconstitution assays with modified proteins.

What methods are available for visualizing RAD51 foci formation after DNA damage?

Visualization of RAD51 foci formation after DNA damage employs several complementary techniques:

• Conventional Immunofluorescence Microscopy:

  • Most commonly used approach

  • Fixed cells are stained with RAD51 antibodies (1-5 μg/ml dilution recommended)

  • Co-staining with γH2AX or 53BP1 identifies sites of DNA damage

  • Typically performed 2-8 hours after damage induction

• Live-Cell Imaging:

  • Uses fluorescently tagged RAD51 (GFP, mCherry fusions)

  • Allows real-time monitoring of foci dynamics

  • CRISPR knock-in strategies preserve endogenous expression levels

  • Photobleaching techniques (FRAP) assess protein mobility

• Super-Resolution Microscopy:

  • Structured Illumination Microscopy (SIM) improves resolution 2-fold

  • Stimulated Emission Depletion (STED) microscopy provides ~50nm resolution

  • Single-molecule localization methods (STORM, PALM) achieve ~20nm resolution

  • Reveals foci substructure not visible with conventional methods

• High-Content Screening Approaches:

  • Automated imaging platforms for quantitative analysis

  • Machine learning algorithms for foci detection and classification

  • Enables large-scale studies across different conditions

• Correlative Light and Electron Microscopy (CLEM):

  • Combines fluorescence imaging with electron microscopy

  • Provides ultrastructural context for RAD51 foci

Sample preparation protocols typically include treating cells with DNA-damaging agents (ionizing radiation, hydroxyurea, etoposide, or mitomycin C), followed by fixation and immunostaining. Quantitative analysis involves measuring foci number, size, intensity, and colocalization with other repair factors.

What are the latest techniques for studying the interaction between RAD51 and BRCA1/BRCA2?

The interaction between RAD51 and BRCA1/BRCA2 can be studied using these state-of-the-art techniques:

• Proximity Ligation Assay (PLA):

  • Detects protein-protein interactions in situ

  • Provides spatial information about interactions within cellular compartments

  • Higher sensitivity than conventional co-immunoprecipitation

  • Can detect transient interactions following DNA damage

• CRISPR-Based Approaches:

  • CRISPR activation/inhibition to modulate expression levels

  • Base editing to introduce specific mutations

  • Tagging endogenous proteins for live imaging

  • Domain-specific mutations to map interaction regions

• Förster Resonance Energy Transfer (FRET):

  • Measures direct protein-protein interactions in living cells

  • Allows real-time monitoring of dynamic interactions

  • Can be combined with fluorescence lifetime imaging (FLIM)

• BioID or APEX Proximity Labeling:

  • Identifies proteins in close proximity to RAD51 in living cells

  • Works by biotinylating nearby proteins for subsequent purification

  • More sensitive than traditional co-immunoprecipitation

  • Captures transient or weak interactions

• Single-Molecule Techniques:

  • Single-molecule pull-down assays

  • Fluorescence correlation spectroscopy (FCS)

  • Total internal reflection fluorescence (TIRF) microscopy

• Structural Biology Methods:

  • Cryo-electron microscopy for complex structures

  • Hydrogen-deuterium exchange mass spectrometry (HDX-MS)

  • Integrative structural modeling approaches

BRCA2 is known to regulate both the intracellular localization and DNA-binding ability of RAD51, which may be important for cellular response to DNA damage . These techniques provide insights into how mutations in BRCA genes affect this critical interaction in cancer contexts.

How does RAD51 overexpression affect genomic stability in experimental models?

RAD51 overexpression has complex effects on genomic stability in experimental models:

• Hyper-recombination Phenotype:

  • Increased frequency of homologous recombination events

  • Elevated sister chromatid exchanges

  • Higher rates of loss of heterozygosity

  • Potential for increased genetic rearrangements

• DNA Damage Response Alterations:

  • Aberrant foci formation even without exogenous damage

  • Prolonged presence of RAD51 at DNA damage sites

  • Interference with other repair pathways

  • Delayed resolution of DNA damage intermediates

• Cell Cycle Effects:

  • Altered cell cycle checkpoint responses

  • Changes in replication fork dynamics

  • Potential replication stress

  • Mitotic defects due to unresolved recombination intermediates

• Cancer-Relevant Phenotypes:

  • RAD51 overexpression promotes progression of cancer and increases its malignancy

  • Stimulates metastasis and increases resistance to chemotherapy

  • Correlates with reduced patient survival in clinical studies

• Experimental Approaches to Study These Effects:

  • Inducible overexpression systems to control timing and level

  • Fluorescence-based reporter assays for recombination events

  • Chromosome spreading techniques to visualize structural abnormalities

  • Single-cell sequencing to detect genomic alterations

  • DNA fiber analysis to assess replication dynamics

These findings highlight the double-edged nature of RAD51 in cancer contexts - while it prevents tumorigenesis by eliminating potentially carcinogenic DNA damage, it can also promote tumors by introducing new mutations when dysregulated .

What are the challenges in developing RAD51 as a therapeutic target?

Developing RAD51 as a therapeutic target presents several challenges:

• Essential Nature of RAD51:

  • Complete inhibition may be toxic to normal cells

  • RAD51 knockout is embryonically lethal in mice

  • Therapeutic window may be narrow

• Complex Regulation:

  • Multiple upstream regulators and post-translational modifications

  • Multiple interaction partners with redundant functions

  • Cell cycle-dependent activity patterns

• Structural Challenges:

  • Few druggable pockets in the protein structure

  • High conservation between species complicates specificity

  • Dynamic nature of RAD51 nucleoprotein filaments

  • Similarity to other recombinases and ATPases

• Delivery Challenges:

  • RAD51 is primarily nuclear, requiring nuclear delivery

  • Targeting specific cancer cells versus normal cells

  • Antibody-based therapies face cellular penetration barriers

• Resistance Mechanisms:

  • Cancer cells may upregulate alternative repair pathways

  • Compensatory expression of RAD51 paralogs

  • Adaptive responses to RAD51 inhibition

Despite these challenges, the dual role of RAD51 in cancer makes it a promising target. RAD51 both prevents tumorigenesis by eliminating potentially carcinogenic DNA damage and promotes tumors by introducing new mutations when overexpressed . Novel approaches like cell-penetrating antibody fragments may help overcome some of these challenges .

How can cell-penetrating RAD51 antibodies be used in research applications?

Cell-penetrating RAD51 antibodies represent an innovative research tool with multiple applications:

• Intracellular Target Accessibility:

  • Novel cell-penetrating peptide "iPTD" fusion enables antibody fragments to effectively enter living cells

  • This opens the door to numerous intracellular targets previously off-limits in living cells

  • High-affinity binding to human RAD51 (KD = 8.1 nM) ensures specificity

• Functional Studies:

  • Inhibits RAD51 ssDNA binding in vitro

  • Creates strong growth inhibitory phenotype in human cells

  • Enhances cell-killing effect of DNA alkylating agents

  • Allows temporal control of RAD51 inhibition

• Experimental Protocols:

  • Can be used at concentrations of 10-100 nM in cell culture

  • Cellular uptake typically occurs within 1-2 hours

  • Effect duration depends on antibody stability (typically 24-48 hours)

  • Compatible with various cell types and experimental conditions

• Advantages Over Other Approaches:

  • More specific than small molecule inhibitors

  • Faster than genetic knockdown approaches

  • Allows acute inhibition studies

  • Can target specific domains or conformations of RAD51

• Combined Applications:

  • Synergistic use with DNA damaging agents

  • Combination with live-cell imaging techniques

  • Paired with other DNA repair inhibitors

  • Potential for development of therapeutic applications

This technology was demonstrated in research showing that a synthetic antibody fragment could effectively enter cells and enhance the cell-killing effect of a DNA alkylating agent . The approach may be similarly useful for other antibody fragments targeting intracellular proteins.