SRFBP1 Antibody

What is SRFBP1 and why is it important in research?

SRFBP1 (Serum response factor-binding protein 1), also known as SRF-dependent transcription regulation-associated protein or p49/STRAP, is involved in regulating transcriptional activation of cardiac genes during aging. It likely plays a role in the biosynthesis and/or processing of SLC2A4 in adipose cells . Recent research has identified SRFBP1 as a critical host factor for Hepatitis C virus (HCV) entry, where it forms a complex with CD81 and coordinates host cell penetration by all seven HCV genotypes . The protein's involvement in both cellular regulation and pathogen entry mechanisms makes it an important target for research across multiple fields including cardiology, metabolism, and virology.

How do I select the appropriate SRFBP1 antibody for my research application?

When selecting an SRFBP1 antibody, consider the following methodological approach:

• Determine your application requirements (WB, IP, ELISA, IF)

  • For Western blot and immunoprecipitation, polyclonal antibodies like ab109598 have demonstrated efficacy with human samples

  • For ELISA applications, CSB-PA839864LA01HU has been specifically validated

• Consider species reactivity needs

  • Most available antibodies are validated for human SRFBP1 detection

  • Check sequence homology if working with non-human samples

• Evaluate immunogen information

  • Some antibodies target C-terminal regions (aa 350 to C-terminus)

  • Others use recombinant fragments (aa 201-429)

• Review validation data

  • Examine Western blot images showing expected band size (49 kDa)

  • Check for cross-reactivity with potential confounding proteins

The final selection should align with your specific experimental requirements and the antibody's validated applications.

What are the optimal conditions for using SRFBP1 antibodies in Western blot analysis?

For optimal Western blot detection of SRFBP1, follow these methodological guidelines:

• Sample preparation:

  • HeLa cell lysates have been successfully used at concentrations of 5-50 μg per lane

  • For liver tissue samples, optimization may be required as SRFBP1 expression can be up to 6-fold higher in primary hepatocytes compared to Huh-7.5 cells

• Antibody dilution:

  • Use primary antibody (e.g., ab109598) at 0.4-1 μg/mL concentration

  • Secondary antibody dilution should be optimized based on detection system

• Detection parameters:

  • Predicted molecular weight is 49 kDa

  • Include positive controls (HeLa lysates) and negative controls (IgG control IP samples)

• Validation considerations:

  • Use siRNA knockdown samples as specificity controls, as demonstrated in HCV studies

  • For quantitative analysis, establish a standard curve with recombinant protein

The above parameters have been validated for human samples, though additional optimization may be required for different cell/tissue types or other species.

How can I effectively use SRFBP1 antibodies for immunoprecipitation experiments?

For successful immunoprecipitation of SRFBP1, implement this methodological approach:

• Lysate preparation:

  • Use 1 mg of total protein per immunoprecipitation reaction

  • Test different lysis buffers as SRFBP1 has both cytoplasmic and membrane associations

• Antibody concentration:

  • For immunoprecipitation, use 6 μg/mL of SRFBP1 antibody (e.g., ab109598)

  • Include IgG controls at equivalent concentrations

• Detection strategy:

  • For immunoblotting detection of immunoprecipitated SRFBP1, use 1 μg/mL antibody concentration

  • Predicted molecular weight is 49 kDa

• Co-immunoprecipitation considerations:

  • When studying SRFBP1 interactions with CD81, consider mild detergent conditions to preserve protein-protein interactions

  • To detect transient interactions, consider chemical crosslinking before cell lysis

This protocol has been validated for detecting both SRFBP1 alone and its interaction partners in human cell lines, particularly in the context of HCV research .

How can I design experiments to study SRFBP1's role in HCV entry?

To investigate SRFBP1's function in HCV entry, implement this comprehensive experimental approach:

• Gene silencing studies:

  • Use validated siRNAs targeting SRFBP1 (positions nt96, nt394, and nt1038 have proven effective)

  • Include appropriate controls: scrambled siRNA (negative) and CD81 siRNA (positive)

  • Verify knockdown efficiency by both RT-qPCR and Western blot

• Infectivity assays:

  • Use HCV pseudoparticles or cell culture-derived HCV

  • Measure infection at early timepoints (24-48h) to focus on entry rather than replication

  • Include controls to distinguish entry from other viral lifecycle stages:

    • PI4KIIIα knockdown (blocks replication)

    • APOE knockdown (blocks assembly/release)

• Colocalization studies:

  • Perform immunofluorescence microscopy to assess SRFBP1 colocalization with:

    • CD81 (Pearson's coefficient ~0.4)

    • CLDN1, OCLN, SR-BI (Pearson's coefficient <0.2)

  • Examine changes in colocalization patterns upon HCV exposure

• Complementation experiments:

  • Express siRNA-resistant SRFBP1 variants to rescue knockdown phenotypes

  • Use domain mutants to identify regions critical for HCV entry

This approach effectively isolates SRFBP1's role in HCV entry from other viral lifecycle stages and has successfully demonstrated that SRFBP1 specifically affects early infection events without altering replication or viral spread to naive cells .

What approaches can identify novel SRFBP1 protein-protein interactions relevant to its biological functions?

To identify and characterize novel SRFBP1 interactions, employ these methodological strategies:

• Quantitative proteomics:

  • Use SILAC (Stable Isotope Labeling by Amino acids in Cell culture) with heavy arginine and lysine labeling

  • Perform CD81 co-immunoprecipitation under different conditions (e.g., ±HCV)

  • Analyze by liquid chromatography-mass spectrometry (LC-MS)

  • Calculate protein abundance ratios between experimental conditions

• Validation of interactions:

  • Confirm direct interactions using reciprocal immunoprecipitation

  • Perform proximity ligation assays to visualize interactions in situ

  • Use FRET or BiFC to examine dynamics of protein interactions

• Functional characterization:

  • Perform siRNA screening of identified interaction partners

  • Measure phenotypic outcomes (e.g., changes in HCV infectivity)

  • Classify interactions as transient or stable based on proteomic data

• Domain mapping:

  • Generate deletion mutants to identify interaction domains

  • Use peptide arrays to map specific binding sequences

This quantitative proteomics approach has successfully identified 26 dynamic CD81 binding partners including SRFBP1, with subsequent validation confirming six as pro-viral host factors .

How do I troubleshoot non-specific binding when using SRFBP1 antibodies?

When encountering non-specific binding with SRFBP1 antibodies, implement this systematic troubleshooting approach:

• Validate antibody specificity:

  • Test antibodies on SRFBP1 knockdown samples

  • Compare results with different SRFBP1 antibodies targeting distinct epitopes

  • Use recombinant SRFBP1 as a positive control

• Optimize blocking conditions:

  • Test different blocking agents (BSA, milk, commercial blockers)

  • Extend blocking time (1-2 hours at room temperature or overnight at 4°C)

  • Add 0.1-0.3% Tween-20 to reduce non-specific hydrophobic interactions

• Adjust antibody conditions:

  • Titrate antibody concentration (try 0.4-1 μg/mL range as validated)

  • Increase washing stringency (more washes, higher salt concentration)

  • Reduce incubation temperature (4°C overnight instead of room temperature)

• Sample preparation considerations:

  • Include protease inhibitors to prevent degradation products

  • For membrane-associated fractions, optimize detergent conditions

  • Pre-clear lysates with Protein A/G beads before immunoprecipitation

For Western blots specifically, a band at 49 kDa represents the expected SRFBP1 size . Non-specific bands may appear due to degradation products or cross-reactivity with related proteins.

How can I distinguish between membrane-associated and cytoplasmic SRFBP1 in my experiments?

To effectively differentiate between membrane-associated and cytoplasmic SRFBP1 pools, employ this methodological approach:

• Subcellular fractionation:

  • Perform differential centrifugation to separate cytosolic, membrane, nuclear, and cytoskeletal fractions

  • Use validated markers for each fraction (e.g., GAPDH for cytosol, Na⁺/K⁺-ATPase for plasma membrane)

  • Analyze SRFBP1 distribution by Western blot

• Immunofluorescence microscopy:

  • Perform co-staining with membrane markers (wheat germ agglutinin, WGA)

  • Use membrane-specific dyes (e.g., DiO, DiI) to visualize co-localization

  • Apply super-resolution techniques (STORM, STED) for precise localization

• Biochemical approaches:

  • Treat cells with membrane-permeabilizing agents (digitonin, saponin) at low concentrations to selectively release cytosolic proteins

  • Use carbonate extraction (pH 11) to distinguish peripheral from integral membrane proteins

  • Apply proteinase K protection assays to identify topology

• Dynamic studies:

  • Track SRFBP1 relocalization upon cellular stimulation or viral exposure

  • Use FRAP (Fluorescence Recovery After Photobleaching) to assess mobility

This combined approach can effectively characterize the dual localization pattern of SRFBP1, which shows both perinuclear and peripheral, vesicular distribution patterns with partial membrane colocalization (Pearson's coefficient with WGA ~0.3) .

How does SRFBP1 expression vary across different cell types and tissues?

SRFBP1 expression exhibits significant tissue and cell-type variation, which can be characterized using these methodological approaches:

• Transcript analysis:

  • RT-qPCR analysis has demonstrated up to 6-fold higher SRFBP1 mRNA levels in primary human hepatocytes compared to Huh-7.5 hepatoma cells

  • Strong correlation between mRNA and protein levels has been observed

• Protein quantification:

  • Western blot with recombinant protein standards for absolute quantification

  • Mass spectrometry-based proteomics for unbiased comparative analysis

• Expression modulation:

  • Overexpression studies in Huh-7.5 cells have shown dose-dependent effects on HCV infectivity

  • Silencing in primary hepatocytes demonstrates functional relevance of endogenous expression levels

• Tissue-specific considerations:

  • Liver expression is functionally relevant for HCV studies

  • Cardiac expression may relate to regulation of cardiac genes during aging

  • Adipose tissue expression suggests roles in glucose transport via SLC2A4 processing

Understanding tissue-specific expression patterns is critical for experimental design, as SRFBP1 levels may be limiting factors in certain model systems, potentially explaining differences between primary cells and cell lines .

What is the relationship between SRFBP1 and CD81 in the context of viral infection?

The relationship between SRFBP1 and CD81 during viral infection can be characterized through these methodological approaches:

• Temporal interaction dynamics:

  • Quantitative proteomics reveals SRFBP1 is recruited to CD81 during HCV uptake

  • This interaction is dynamic and HCV-dependent, categorized as a "transient CD81 interaction partner"

• Spatial colocalization:

  • Immunofluorescence microscopy shows SRFBP1 colocalizes with CD81 (Pearson's coefficient ~0.4)

  • Colocalization is observed in perinuclear regions and in punctate, vesicular patterns at the cell periphery

  • SRFBP1 does not significantly colocalize with other HCV entry factors (CLDN1, OCLN, SR-BI)

• Functional relationship:

  • SRFBP1 silencing does not alter CD81 surface expression

  • SRFBP1 is not a chaperone or transcriptional regulator of known HCV entry factors

  • SRFBP1 facilitates host cell penetration by all seven HCV genotypes, but not by vesicular stomatitis virus or human coronavirus

• Mechanistic insights:

  • SRFBP1 acts during early infection steps but does not affect viral replication or spread

  • The interaction appears specific to HCV entry mechanisms rather than general endocytosis

These findings suggest SRFBP1 functions as an HCV-specific, pan-genotypic host entry factor that forms a complex with CD81 during viral entry without affecting receptor expression levels .

How might SRFBP1-targeting approaches be developed for antiviral therapeutics?

Developing SRFBP1-targeting antiviral strategies requires consideration of these methodological approaches:

• Target validation:

  • Confirm SRFBP1's essential role across:

    • Different viral genotypes (all seven HCV genotypes are dependent)

    • Primary human hepatocytes (not just cell lines)

    • Patient-derived viral isolates

• Therapeutic targeting strategies:

  • Small molecule inhibitors:

    • Screen for compounds disrupting SRFBP1-CD81 interaction

    • Develop structure-activity relationships through medicinal chemistry

  • Peptide-based approaches:

    • Design competitive inhibitors based on interaction domains

    • Use phage display to identify high-affinity binding peptides

  • RNA therapeutics:

    • Optimize siRNA delivery to hepatocytes

    • Evaluate antisense oligonucleotides targeting SRFBP1 mRNA

• Specificity considerations:

  • Evaluate effects on SRFBP1's physiological functions in:

    • Cardiac gene regulation during aging

    • Glucose transport (SLC2A4) in adipose tissue

  • Screen for potential off-target effects on related proteins

• Combination approaches:

  • Test synergy with direct-acting antivirals

  • Evaluate resistance development through serial passage experiments

Since SRFBP1 facilitates entry of all HCV genotypes but not other viruses like VSV and human coronavirus , it represents a potentially specific target for pan-genotypic HCV entry inhibitors with minimal impact on host cellular processes.

What technologies could enhance our understanding of SRFBP1's structural interactions with viral and host proteins?

Advanced structural biology approaches to elucidate SRFBP1 interactions include:

• High-resolution structural analysis:

  • Cryo-electron microscopy of SRFBP1-CD81 complexes

  • X-ray crystallography of interaction domains

  • NMR spectroscopy for dynamic interaction mapping

  • AlphaFold2 or RoseTTAFold prediction followed by experimental validation

• Molecular interaction mapping:

  • Hydrogen-deuterium exchange mass spectrometry (HDX-MS) to identify interaction surfaces

  • Cross-linking mass spectrometry (XL-MS) to capture transient interactions

  • Surface plasmon resonance (SPR) for binding kinetics

  • Isothermal titration calorimetry (ITC) for thermodynamic parameters

• Live-cell visualization:

  • Single-molecule tracking of fluorescently labeled SRFBP1 during viral entry

  • FRET-based biosensors to detect conformational changes upon binding

  • Lattice light-sheet microscopy for 4D visualization of protein dynamics

  • Correlative light and electron microscopy (CLEM) for ultrastructural context

• Functional genomics integration:

  • CRISPR-Cas9 domain mapping through targeted mutagenesis

  • Deep mutational scanning to identify critical residues

  • Proteomic profiling of interaction networks under various conditions