Hus1 Antibody

What is HUS1 and what is its biological significance?

HUS1 is a component of the evolutionarily conserved 9-1-1 (RAD9-RAD1-HUS1) cell-cycle checkpoint response complex that plays a critical role in DNA repair mechanisms. The 9-1-1 complex functions as a DNA damage sensor and is recruited to DNA lesions upon damage by the RAD17-replication factor C (RFC) clamp loader complex. Once recruited, it acts as a sliding clamp platform on DNA for several proteins involved in long-patch base excision repair (LP-BER). This complex plays an apical role in the DNA damage response, and loss of a functional complex affects many downstream checkpoint pathways . The 9-1-1 complex is also a key component involved in the activation of the ATR pathway, forming a ring-shaped heterotrimer that resembles the homotrimeric sliding clamp proliferating cell nuclear antigen (PCNA) .

What are the basic molecular characteristics of the HUS1 protein?

HUS1 (HUS1 checkpoint homolog, S. pombe) is a protein with the following key characteristics:

• Calculated molecular weight: 32 kDa

• Observed molecular weight: 32 kDa

• Gene ID (NCBI): 3364

• UniProt ID: O60921

• GenBank accession number: BC007013

The protein forms a heterotrimeric complex with checkpoint proteins RAD9 and RAD1, which is essential for cell cycle arrest in response to DNA damage .

What applications are HUS1 antibodies typically used for in research?

HUS1 antibodies are primarily used for the following applications:

• Western Blotting (WB): Typically at dilutions ranging from 1:1000-1:6000

• Immunohistochemistry (IHC): Generally at dilutions of 1:150-1:600

• Immunoprecipitation (IP): Recommended dilution around 1:200

• Flow Cytometry (intracellular): For detection of HUS1 within cells

• ELISA: For quantitative detection of HUS1 protein

It is recommended that researchers titrate these antibodies in each testing system to obtain optimal results, as the ideal dilution may be sample-dependent .

What cell lines have been validated for HUS1 antibody detection?

Based on the search results, HUS1 antibodies have been successfully validated for Western blot detection in several human cell lines, including:

• HeLa cells

• HEK-293 cells (and 293T)

• A549 cells

• U2OS cells

• Jurkat cells

• K-562 cells

• C8D30 cells

For immunohistochemistry applications, positive detection has been confirmed in human prostate cancer tissue samples .

What are the proper storage conditions for HUS1 antibodies?

Most HUS1 antibodies should be stored at -20°C for long-term storage. They are typically stable for one year after shipment when stored properly. For short-term storage, 4°C is appropriate. Researchers should avoid repeated freeze/thaw cycles as this can lead to protein denaturation and reduced antibody performance . Many commercially available HUS1 antibodies are supplied in storage buffers containing:

• PBS with 0.02% sodium azide and 50% glycerol, pH 7.3

• 0.1M tris glycine with 20% glycerol and 0.01% thimerosal, pH 7

These buffer components help maintain antibody stability during storage.

How does the 9-1-1 complex functionally interact with other DNA repair proteins?

The 9-1-1 complex (which includes HUS1) has several sophisticated interactions with other DNA repair machinery:

• Interaction with TopBP1: The 9-1-1 complex interacts with DNA topoisomerase 2-binding protein 1 (TopBP1) in response to DNA damage, activating ATR and causing signal amplification through further recruitment of TopBP1 .

• Role in mismatch repair: The complex interacts with DNA mismatch repair proteins MSH2, MSH3, and MSH6 to play a role in mismatch repair mechanisms .

• Involvement in DNA damage tolerance: During error-free DNA damage tolerance processes, the 9-1-1 complex cooperates with polyubiquitinated PCNA and Exo1 nuclease to support switching of the replicative polymerase to the undamaged template .

• Enhancement of repair enzyme activities: The 9-1-1 complex stimulates multiple enzymes involved in DNA repair:

  • DNA polymerase beta (POLB) activity by increasing its affinity for the 3'-OH end of the primer-template

  • Stabilizes POLB at sites where LP-BER proceeds

  • Enhances endonuclease FEN1 cleavage activity on substrates with double, nick, or gap flaps of distinct sequences and lengths

  • Promotes DNA ligase I (LIG1) activity on long-patch base excision repair substrates

• Double-strand break repair: The 9-1-1 complex is necessary for the recruitment of RHNO1 to sites of double-stranded breaks (DSB) occurring during the S phase .

What are the key considerations for optimizing antigen retrieval in HUS1 immunohistochemistry?

Optimizing antigen retrieval is critical for successful HUS1 detection in tissue samples. Based on the available data:

• Buffer selection: For human prostate cancer tissue samples, it is suggested to use TE buffer at pH 9.0 for optimal antigen retrieval .

• Alternative approach: As an alternative, citrate buffer at pH 6.0 may be used, though this might yield different results compared to the recommended TE buffer .

• Protocol optimization: The specific heating time, temperature, and cooling period should be optimized based on tissue type, fixation method, and section thickness. A typical approach involves:

  • Deparaffinization and rehydration of sections

  • Immersion in the appropriate retrieval buffer

  • Heating (95-100°C) for 15-20 minutes

  • Gradual cooling to room temperature

  • Proceeding with immunostaining protocol

• Tissue-specific considerations: Different tissue types may require modifications to the antigen retrieval protocol to minimize background staining while maximizing specific signal.

How can researchers differentiate between non-specific signals and true HUS1 detection in Western blotting?

Distinguishing between specific and non-specific signals is a common challenge when working with HUS1 antibodies:

• Expected molecular weight: The calculated and observed molecular weight of HUS1 is approximately 32 kDa. Any band at this molecular weight is potentially specific HUS1 signal .

• Additional bands: Some HUS1 antibodies may detect a 45 kDa band of unknown origin in certain cell lysates. This should be noted when interpreting results .

• Positive controls: Using validated cell lines such as HeLa, HEK-293, A549, or U2OS as positive controls can help establish the expected band pattern for true HUS1 detection .

• Blocking optimization: Adjusting blocking conditions (buffer composition, blocking time) can help reduce non-specific binding while preserving specific signals.

• Antibody validation: Using multiple antibodies targeting different epitopes of HUS1 can confirm the specificity of detected bands.

• Knockdown/knockout controls: Including samples from cells with HUS1 knockdown or knockout can provide definitive evidence for band specificity.

What are the recommended protocols for HUS1 detection in Western blotting?

For optimal Western blot detection of HUS1, researchers should consider the following methodological aspects:

• Sample preparation:

  • Lyse cells in an appropriate buffer containing protease inhibitors

  • Determine protein concentration and load equal amounts per lane (typically 20-50 μg)

  • Denature samples by heating at 95°C for 5 minutes in loading buffer containing SDS and a reducing agent

• Gel electrophoresis and transfer:

  • Use 10-12% SDS-PAGE gels for optimal resolution around 32 kDa

  • Transfer to PVDF or nitrocellulose membranes using standard transfer conditions

  • Verify transfer efficiency with reversible protein stains

• Blocking and antibody incubation:

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

  • Incubate with primary HUS1 antibody at recommended dilutions (1:1000-1:6000) overnight at 4°C

  • Wash extensively with TBST

  • Incubate with appropriate HRP-conjugated secondary antibody

  • Wash and develop using chemiluminescence detection

• Controls and validation:

  • Include positive control lysates (HeLa, HEK-293, etc.)

  • Consider including loading controls (β-actin, GAPDH, etc.)

  • For validation of specificity, consider using HUS1 knockdown/knockout samples

What are the critical factors affecting immunohistochemical detection of HUS1 in tissue samples?

Several critical factors influence the success of HUS1 detection in tissue samples:

• Fixation method and duration: Overfixation can mask epitopes, while underfixation may result in poor tissue morphology. Formalin-fixed, paraffin-embedded tissues typically require appropriate antigen retrieval.

• Antigen retrieval: TE buffer at pH 9.0 is recommended, with citrate buffer at pH 6.0 as an alternative .

• Antibody dilution: For immunohistochemistry, HUS1 antibodies are typically used at dilutions ranging from 1:150 to 1:600 . Titration experiments are recommended to determine optimal dilution for each tissue type.

• Detection system: Choose an appropriate detection system (e.g., polymer-based, ABC method) compatible with the primary antibody species and isotype.

• Incubation conditions: Primary antibody incubation is typically performed overnight at 4°C or for 1-2 hours at room temperature.

• Counterstaining: Optimize counterstaining (e.g., hematoxylin) to provide context for HUS1 staining without obscuring specific signals.

• Controls: Include positive control tissues (human prostate cancer has been validated) and negative controls (primary antibody omission) in each staining run.

How can researchers effectively troubleshoot issues with HUS1 immunoprecipitation experiments?

Immunoprecipitation of HUS1 may present unique challenges due to its involvement in protein complexes. Consider these troubleshooting strategies:

• Low immunoprecipitation efficiency:

  • Increase antibody amount (starting recommendation is 1:200 dilution)

  • Extend incubation time with antibody (overnight at 4°C)

  • Verify antibody compatibility with IP applications

  • Consider using magnetic beads instead of agarose for improved recovery

• Co-immunoprecipitation of interacting partners:

  • To preserve protein-protein interactions (e.g., with RAD9 and RAD1), use gentle lysis buffers

  • Cross-linking may be necessary to capture transient interactions

  • Adjust salt concentration to balance between specific and non-specific interactions

• High background:

  • Pre-clear lysates with beads alone before adding antibody

  • Include additional wash steps with increasing stringency

  • Optimize blocking conditions with BSA or non-fat dry milk

• Verification of results:

  • Probe immunoprecipitates for known HUS1 interacting partners (RAD9, RAD1)

  • Consider reverse co-IP experiments to validate interactions

  • Include negative controls (isotype control antibody or IgG)

How can researchers design experiments to study HUS1 function in response to different DNA damaging agents?

To investigate HUS1's role in various DNA damage response pathways:

• Selection of DNA damaging agents:

  • UV radiation: Primarily induces pyrimidine dimers

  • Ionizing radiation: Causes double-strand breaks

  • Hydroxyurea: Depletes nucleotide pools and induces replication stress

  • Methyl methanesulfonate (MMS): Alkylating agent that causes base modifications

  • Cisplatin: Forms DNA crosslinks

• Experimental design considerations:

  • Time-course experiments to track HUS1 recruitment to damage sites

  • Dose-response studies to determine threshold levels for HUS1 activation

  • Cell synchronization to examine cell cycle-specific responses

  • Combinatorial treatments to investigate pathway crosstalk

• Readouts and analytical methods:

  • Immunofluorescence to track HUS1 localization following damage

  • Chromatin immunoprecipitation to assess HUS1 recruitment to specific genomic regions

  • Co-immunoprecipitation to identify damage-specific interaction partners

  • Western blotting to monitor HUS1 post-translational modifications

  • Cell viability assays to correlate HUS1 function with cellular outcomes

• Genetic manipulation approaches:

  • CRISPR/Cas9-mediated knockout or knockin of HUS1 variants

  • siRNA or shRNA knockdown to assess dose-dependent effects

  • Expression of dominant-negative HUS1 mutants

What methodological approaches can be used to study the dynamics of 9-1-1 complex formation?

The dynamics of 9-1-1 complex assembly and function can be studied using:

• Real-time imaging techniques:

  • Fluorescence recovery after photobleaching (FRAP) with fluorescently tagged HUS1

  • Förster resonance energy transfer (FRET) between tagged 9-1-1 components

  • Live-cell imaging of recruitment kinetics following localized DNA damage

• Biochemical approaches:

  • Size exclusion chromatography to isolate intact complexes

  • Velocity sedimentation to analyze complex assembly

  • Sequential immunoprecipitation to isolate specific sub-complexes

  • Protein crosslinking followed by mass spectrometry

• Structural biology methods:

  • Cryo-electron microscopy of the assembled 9-1-1 complex

  • X-ray crystallography of individual components and subcomplexes

  • Hydrogen-deuterium exchange mass spectrometry to probe dynamic regions

• Quantitative proteomics:

  • SILAC (Stable Isotope Labeling with Amino acids in Cell culture) to quantify damage-induced changes in complex composition

  • Parallel reaction monitoring to track specific post-translational modifications

How can researchers analyze conflicting data regarding HUS1 expression or function in different experimental systems?

When faced with conflicting results across different experimental systems:

• Systematic comparison of experimental conditions:

  • Cell type differences (primary vs. immortalized, tissue of origin)

  • Culture conditions (serum levels, oxygen tension, confluence)

  • Experimental timing (acute vs. chronic treatments, cell cycle stage)

  • Reagent variations (antibody clones, detection methods)

• Technical validation approaches:

  • Use multiple antibodies targeting different epitopes of HUS1

  • Employ alternative detection methods (e.g., mass spectrometry)

  • Include genetic validation (knockout controls, rescue experiments)

  • Quantify results using different normalization strategies

• Biological context considerations:

  • HUS1 functions may vary across tissue types or developmental stages

  • Alternative splicing or post-translational modifications may affect detection

  • Protein complex formation may mask or expose epitopes

  • Subcellular localization may differ based on cellular state

• Statistical and reporting considerations:

  • Perform power calculations to ensure adequate sample sizes

  • Use appropriate statistical tests for the data distribution

  • Consider meta-analysis approaches when comparing across studies

  • Report all relevant experimental details to enable reproduction