fbxl5 Antibody

What is FBXL5 and why is it significant for research in iron metabolism?

FBXL5 (F-box and leucine-rich repeat protein 5) is a component of the SCF (SKP1-cullin-F-box) protein ligase complex that plays a central role in iron homeostasis by promoting the ubiquitination and subsequent degradation of iron regulatory proteins, particularly IREB2/IRP2 . FBXL5 functions as a critical iron and oxygen sensor through two key domains: its N-terminal hemerythrin-like (Hr) region containing a diiron metal center that responds to iron availability, and its C-terminal domain containing a redox-sensitive [2Fe-2S] cluster that mediates oxygen sensing .

The significance of FBXL5 lies in its regulatory function in iron metabolism. When intracellular iron levels rise, the Hr region stabilizes, and the [2Fe-2S] cluster assembles in the C-terminal domain. This configuration allows FBXL5 to recruit IRP2 as a substrate for polyubiquitination and degradation, but only when oxygen levels are sufficient to maintain the cluster in its oxidized state . Through this mechanism, FBXL5 coordinates cellular responses to both iron and oxygen availability.

What applications are FBXL5 antibodies validated for in research settings?

FBXL5 antibodies have been validated for several key applications in molecular and cellular biology research:

For Western blot applications, FBXL5 antibodies typically detect a band at approximately 78-79 kDa, corresponding to the predicted molecular weight of the FBXL5 protein . In immunohistochemistry applications, antigen retrieval by heat mediation in Tris pH 9 has been demonstrated to be effective for optimal staining results .

How should FBXL5 antibodies be validated before use in experimental protocols?

A robust validation strategy for FBXL5 antibodies should include:

• Positive control testing: Use samples known to express FBXL5, such as human fetal testis tissue or cell lines with confirmed FBXL5 expression .

• Knockdown/knockout verification: Conduct siRNA-mediated knockdown of FBXL5 to confirm specificity. The search results demonstrate that FBXL5 siRNA treatment significantly increases the levels of IRP1 3C>3S protein and endogenous IRP2 protein, providing a functional validation of antibody specificity .

• Reactivity confirmation: If working with non-human samples, confirm cross-reactivity based on sequence homology. Many commercially available FBXL5 antibodies react with human, mouse, and rat samples .

• Application-specific validation: For Western blot applications, verify the correct molecular weight (approximately 78-79 kDa) and band pattern . For IHC applications, include appropriate negative controls and test multiple dilutions.

• Batch testing: Due to potential batch-to-batch variations, validate each new lot against previously validated antibodies using consistent positive control samples.

What are optimal sample preparation protocols for experiments using FBXL5 antibodies?

For effective sample preparation when working with FBXL5 antibodies:

For Western Blot analysis:

• Prepare cell/tissue lysates in a buffer containing protease inhibitors to prevent degradation of FBXL5.

• For enhanced detection of FBXL5-protein interactions, consider including proteasome inhibitors (e.g., MG132 at 5 μM for 4 hours) prior to extraction .

• Adjust protein concentration to approximately 3 mg/ml for consistent results .

• For optimal separation, use SDS-PAGE with gradient gels (e.g., 4-12%) as FBXL5 is a relatively large protein (~78.6 kDa) .

For Immunohistochemistry:

• Fix tissue samples with formaldehyde and embed in paraffin.

• Block with 1% BSA for 1 hour at room temperature.

• Perform antigen retrieval by heat mediation in Tris pH 9 buffer.

• Incubate with primary FBXL5 antibody (typically at 1/100 dilution in 1% BSA + 1% FBS in TBS) for 16 hours .

• Use HRP-conjugated secondary antibodies for detection.

How can iron manipulation experiments be designed to study FBXL5 regulation?

Iron manipulation experiments are crucial for understanding FBXL5's role as an iron sensor. Here is a methodological approach:

Iron Depletion Protocol:

• Treat cells with iron chelators such as deferoxamine (DFO) at 100-200 μM for 16-24 hours.

• Monitor FBXL5 protein levels by Western blot, expecting decreased stability and lower protein levels under iron-depleted conditions .

• Simultaneously track IRP2 levels, which should increase inversely to FBXL5 reduction.

Iron Supplementation Protocol:

• Treat cells with ferric ammonium citrate (FAC) at 100-200 μM for 16-24 hours.

• Analyze FBXL5 stabilization by Western blot, expecting increased protein levels.

• Track the formation of SCF complexes through co-immunoprecipitation of FBXL5 with other SCF components.

Research findings show that iron treatment blocks the decrease in cell viability in response to impaired CIA (Cytosolic Iron-sulfur cluster Assembly) and FBXL5 function, and is associated with an increase in FBXL5 protein levels . This indicates that iron supplementation stabilizes FBXL5, promoting its protective function in cellular iron homeostasis.

What approaches are effective for studying FBXL5-IRP interactions?

To study the regulatory interactions between FBXL5 and Iron Regulatory Proteins (IRPs):

Co-immunoprecipitation Protocol:

• Treat cells with proteasome inhibitors (MG132, 5 μM) for 4 hours prior to lysis to prevent degradation of interaction complexes .

• Prepare cell lysates in buffer containing 150 mM NaCl, 20 mM Tris-HCl (pH 7.5), 1% Triton X-100, with protease inhibitors.

• Incubate lysates with anti-FBXL5 antibodies conjugated to agarose beads for 30 minutes at 4°C.

• Wash immunoprecipitates and analyze by Western blot for co-precipitated IRP1 and IRP2 .

RNA Electrophoretic Mobility Shift Assay (RNA-EMSA) for IRP Activity:

• Prepare cytoplasmic extracts from cells with various treatments affecting FBXL5 levels.

• Incubate extracts with radiolabeled IRE (Iron Responsive Element) RNA probes.

• Analyze binding activities through gel shift assays with and without 2-mercaptoethanol (2-ME) treatment.

• Include supershift with IRP1-specific antibodies to differentiate between IRP1 and IRP2 binding activities .

Research data indicates that knocking down FBXL5 significantly increases IRP1 3C>3S protein levels and endogenous IRP2 protein levels . Additionally, studies have shown that CIA inhibition or induction of either IRP1 or IRP2 is associated with increased FBXL5 protein levels, demonstrating a feedback loop that limits the overaccumulation of either IRP .

How can researchers investigate the role of FBXL5 in the ubiquitin-proteasome pathway?

To examine FBXL5's function in the ubiquitin-proteasome pathway:

In Vitro Ubiquitination Assay:

• Purify recombinant FBXL5 as part of the SCF complex.

• Combine with E1, E2 enzymes, ubiquitin, ATP, and purified substrate proteins (e.g., IRP2).

• Incubate at 30°C for 1-2 hours and analyze ubiquitination by Western blot.

• Include controls with mutated FBXL5 or without individual components to confirm specificity.

Proteasomal Degradation Analysis:

• Treat cells with cycloheximide (100 μg/ml) to inhibit protein synthesis.

• Collect samples at different time points (0, 2, 4, 6, 8 hours).

• Analyze the degradation rate of FBXL5 substrates by Western blot.

• Compare degradation rates between wild-type cells and cells with FBXL5 knockdown .

FBXL5 Substrate Identification:

• Express FLAG-tagged FBXL5 in cells using retroviral vectors.

• Immunoprecipitate FBXL5 complexes using anti-FLAG antibodies.

• Identify interacting proteins by liquid chromatography-tandem mass spectrometry (LC-MS/MS) .

• Validate potential substrates through in vitro and in vivo ubiquitination assays.

Research shows that FBXL5 negatively regulates DNA damage response by mediating the ubiquitin-proteasome degradation of DNA repair protein NABP2 . Additionally, FBXL5 promotes the ubiquitination of SNAI1 within the nucleus, preventing its interaction with DNA and promoting its degradation .

What methods are recommended for investigating FBXL5 regulation by HERC2?

To study how HERC2 regulates FBXL5 stability:

HERC2-FBXL5 Interaction Analysis:

• Incubate cells with proteasome inhibitor MG132 (5 μM) for 4 hours to stabilize protein interactions.

• Prepare cell lysates and immunoprecipitate with antibodies against HERC2 or FBXL5.

• Analyze co-precipitation by Western blot to detect endogenous protein interactions .

HERC2 Knockdown Effects:

• Transfect cells with siRNA targeting HERC2.

• Analyze FBXL5 protein levels and stability by Western blot.

• Measure changes in IRP2 levels and iron metabolism markers (ferritin, transferrin receptor).

• Assess cellular iron content using colorimetric assays or inductively coupled plasma mass spectrometry (ICP-MS).

Ubiquitination Analysis:

• Co-express FBXL5 with wild-type or catalytically inactive HERC2.

• Immunoprecipitate FBXL5 under denaturing conditions.

• Detect ubiquitination patterns by Western blot using anti-ubiquitin antibodies.

Research demonstrates that HERC2, a HECT-type E3 ligase, binds to FBXL5 and regulates its stability, thus controlling iron metabolism by promoting ubiquitin-dependent degradation of FBXL5 . This provides an additional layer of regulation in the control of cellular iron homeostasis.

What strategies help resolve contradictory results when using different FBXL5 antibodies?

When faced with contradictory results using different FBXL5 antibodies:

Epitope Mapping Analysis:

• Compare the immunogens used to generate different antibodies.

• Test antibodies against recombinant FBXL5 fragments to determine epitope recognition patterns.

• For the antibodies described in the search results, some target the C-terminus (amino acids 500 to C-terminus) while others target the middle region or amino acids 1-310 .

Cross-Validation Protocol:

• Use multiple antibodies targeting different epitopes of FBXL5 in parallel experiments.

• Include genetic controls (FBXL5 knockdown/knockout) to confirm specificity.

• Compare results across different experimental conditions (iron-replete vs. iron-depleted).

• Validate findings with complementary techniques (e.g., mass spectrometry, RNA analysis).

Influence of Post-Translational Modifications:

• Investigate whether discrepancies might be due to antibodies differentially detecting modified forms of FBXL5.

• Use phosphatase treatment or iron/oxygen manipulation to alter FBXL5 modification status.

• Consider that iron-dependent conformational changes in FBXL5 might affect epitope accessibility .

The search results indicate that FBXL5 undergoes conformational changes under iron deficiency conditions, which could affect antibody recognition . Additionally, different applications (WB vs. IHC) may require antibodies with different characteristics for optimal performance.

How can researchers investigate the redox-sensitive [2Fe-2S] cluster in FBXL5?

To study the critical redox-sensitive [2Fe-2S] cluster in FBXL5:

Spectroscopic Analysis:

• Purify recombinant FBXL5 C-terminal domain under anaerobic conditions.

• Analyze the [2Fe-2S] cluster using UV-visible spectroscopy, electron paramagnetic resonance (EPR), and Mössbauer spectroscopy.

• Monitor spectral changes upon oxidation/reduction to characterize the redox properties.

Oxygen Sensitivity Experiments:

• Prepare cells in hypoxic chambers with varying oxygen concentrations (1%, 5%, 21%).

• Analyze FBXL5 protein levels and IRP2 degradation rates by Western blot.

• Use site-directed mutagenesis to modify the cysteine residues coordinating the [2Fe-2S] cluster and assess functional consequences.

Combined Iron/Oxygen Manipulation:

• Treat cells with iron chelators or supplements under normoxic vs. hypoxic conditions.

• Monitor FBXL5 stability, IRP2 levels, and target gene expression.

• Use polysome profiling to assess the impact on translation of iron metabolism genes.

Research findings indicate that the C-terminal domain of FBXL5 contains a redox-sensitive [2Fe-2S] cluster that, upon oxidation, promotes binding to IRP2 to effect its oxygen-dependent degradation . Only when oxygen levels are high enough to maintain the cluster in its oxidized state can FBXL5 recruit IRP2 as a substrate for polyubiquitination and degradation .

What methods are recommended for studying the synergistic role of IRP1 and FBXL5 in coordinating iron metabolism?

To investigate the coordinated functions of IRP1 and FBXL5:

Combined Genetic Manipulation:

• Perform single and combined knockdowns of FBXL5, NUBP2 (CIA component), and FAM96A (CIA specificity factor for IRP1).

• Analyze cell viability, iron content, and expression of iron metabolism genes.

• Rescue experiments with iron supplementation to determine specific effects .

IRP1 Phosphorylation Analysis:

• Detect Ser-138 phosphorylation of IRP1 using phospho-specific antibodies.

• Compare phosphorylation levels between cells with normal or inhibited CIA activity.

• Assess the requirement of this phosphorylation for iron-mediated rescue of cell growth .

CIA System Function Analysis:

• Monitor IRP1 RNA-binding activity using RNA-EMSA with or without 2-ME treatment.

• Analyze the effect of CIA inhibition on total IRP RNA-binding activity.

• Study the impact of FBXL5 knockdown on reversing decreased IRP1 RNA-binding activity when CIA is inhibited .

Research data shows that knockdown of FBXL5 itself fails to affect cell viability, but cell growth is strongly inhibited when this is combined with expression of an IRP1 mutant with constitutive RNA binding or if CIA activity is impaired by suppression of either NUBP2 or FAM96A . Additionally, iron treatment blocks the decrease in cell viability in response to impaired CIA and FBXL5 function . This reveals a regulatory circuit involving FBXL5 and CIA that acts through both IRPs to control iron metabolism and promote optimal cell growth .

How can researchers optimize Western blot protocols specifically for FBXL5 detection?

For optimal Western blot detection of FBXL5:

Sample Preparation Optimization:

• Include proteasome inhibitors (MG132, 5 μM) for 4-6 hours before harvesting cells to stabilize FBXL5 .

• Use a lysis buffer containing 150 mM NaCl, 20 mM Tris-HCl (pH 7.5), 1% Triton X-100 with complete protease inhibitor cocktail.

• Perform protein extraction at 4°C to minimize degradation.

• For iron-dependent studies, prepare samples under both iron-replete and iron-depleted conditions.

Blotting Protocol Optimization:

• Use 8% or 4-12% gradient gels for optimal resolution of the 78-79 kDa FBXL5 protein .

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

• Block with 5% non-fat dry milk in TBST for 1 hour at room temperature.

• Incubate with primary FBXL5 antibody at 1:500-1:1,000 dilution overnight at 4°C .

• Use HRP-conjugated anti-rabbit secondary antibody (1:5,000) for detection .

Troubleshooting Weak Signals:

• Increase protein loading (up to 50-80 μg per lane).

• Extend primary antibody incubation time to 16-24 hours at 4°C.

• Try enhanced chemiluminescence (ECL) systems with higher sensitivity.

• Consider using signal enhancers like Western Blot Signal Enhancer.

Based on available data, researchers have successfully detected FBXL5 in human fetal testis lysate with a predicted band size of 78 kDa using antibody dilutions of 1:1000 .

What controls are essential when studying FBXL5-mediated protein degradation?

When investigating FBXL5-mediated protein degradation:

Essential Controls for Degradation Studies:

Substrate Specificity Validation:

• Perform co-immunoprecipitation of FBXL5 with putative substrate proteins.

• Compare degradation rates of wild-type substrate vs. mutants lacking FBXL5 recognition motifs.

• Reconstitute the degradation system in vitro with purified components.

• Include controls with other F-box proteins to confirm specificity.

Research demonstrates that FBXL5 promotes ubiquitination and subsequent degradation of various proteins including IREB2/IRP2, DCTN1, SNAI1, and NABP2 . The search results also show that knockdown of FBXL5 significantly increases the levels of IRP1 3C>3S protein and endogenous IRP2 protein, confirming the role of FBXL5 in their degradation .

What emerging techniques might advance our understanding of FBXL5 function in iron homeostasis?

Several cutting-edge approaches show promise for advancing FBXL5 research:

CRISPR-Cas9 Genome Editing:

• Generate precise point mutations in the iron-sensing hemerythrin domain or [2Fe-2S] cluster coordination sites.

• Create conditional knockouts to study tissue-specific functions of FBXL5.

• Implement CRISPR interference (CRISPRi) or activation (CRISPRa) to modulate FBXL5 expression levels.

Proximity Labeling Proteomics:

• Express FBXL5 fused to BioID2 or TurboID in cells under various iron conditions.

• Identify proteins that interact with FBXL5 in an iron-dependent manner.

• Map the dynamic interactome of FBXL5 during iron fluctuations.

Single-Cell Analysis:

• Examine cell-to-cell variability in FBXL5 expression and function.

• Correlate FBXL5 levels with cellular iron content at the single-cell level.

• Identify subpopulations with distinct iron regulatory strategies.

Structural Biology Approaches:

• Utilize cryo-electron microscopy to visualize the SCF-FBXL5 complex with its substrates.

• Determine high-resolution structures of FBXL5 in both iron-bound and iron-free states.

• Perform molecular dynamics simulations to understand conformational changes upon iron binding.

Research indicates that FBXL5 operates within a complex environment and serves as a sensor for both iron and oxygen levels, influencing the translation of mRNAs coding for proteins involved in iron metabolism . Advancing our understanding of these complex regulatory mechanisms will require integration of multiple advanced techniques.