vps13b Antibody

What is the functional role of VPS13B protein in cellular physiology?

VPS13B mediates the transfer of lipids between membranes at organelle contact sites and binds phosphatidylinositol 3-phosphate. It functions as a tethering factor in the slow endocytic recycling pathway, assisting traffic between early and recycling endosomes . The protein plays a crucial role in the assembly of the Golgi apparatus by mediating trafficking to the Golgi membrane . Additionally, VPS13B is involved in nervous system development, potentially required for neuron projection development, and may contribute to adipose tissue development .

Which cellular compartments show VPS13B localization?

VPS13B is predominantly localized at the cis-trans Golgi complex interface. Advanced imaging studies using DNA-PAINT super-resolution microscopy reveal that VPS13B is positioned closest to cis-Golgi markers GM130 (approximately 28 nm) and GRASP65 (approximately 33 nm), and furthest from trans-Golgi markers TGN46 and Golgin97 . VPS13B is not localized at the interface of the cis-Golgi complex with the intermediate compartment and ER, but rather on portions of the cis-Golgi complex distal to this interface . Recent research has also suggested possible VPS13B involvement in Golgi-lipid droplet contacts that associate with the endoplasmic reticulum .

What are the recommended applications for VPS13B antibodies?

Based on validated commercial antibodies, VPS13B antibodies are suitable for multiple applications:

Note: Optimal dilutions should be determined experimentally for each specific antibody and application .

How can I validate the specificity of a VPS13B antibody?

Validation of VPS13B antibody specificity requires a multi-faceted approach:

• Genetic knockdown/knockout controls: Compare staining in wild-type cells with VPS13B-depleted cells (siRNA, CRISPR-Cas9)

• Subcellular localization verification: Confirm co-localization with established Golgi markers (particularly GM130 and GRASP65)

• Western blot validation: Verify detection of the expected molecular weight band (approximately 449 kDa for full-length protein)

• Peptide competition assay: Pre-incubation with the immunizing peptide should abolish specific signals

• Cross-reactivity assessment: Test the antibody against recombinant protein fragments in protein arrays (comprehensive testing includes arrays of 364+ human recombinant protein fragments)

Notably, due to low levels of endogenous VPS13B expression, validation may be enhanced by using cells transfected with codon-optimized versions of full-length human VPS13B fused to tags like GFP or Halo .

What fixation and antigen retrieval methods work best for VPS13B immunostaining?

For optimal VPS13B immunostaining:

Fixation protocols:

• For cell lines: 4% paraformaldehyde (PFA) for 15-20 minutes at room temperature

• For tissue sections: 10% neutral buffered formalin, followed by paraffin embedding

Antigen retrieval recommendations:

• Primary method: TE buffer (pH 9.0) is recommended for heat-induced epitope retrieval

• Alternative method: Citrate buffer (pH 6.0) may also be effective for some antibodies

Nuclear counterstaining:

• 6-Diamidino-2-phenylindole (DAPI) is commonly used for nuclear DNA staining alongside VPS13B immunofluorescence

How can I accurately quantify VPS13B localization to the Golgi complex?

Quantification of VPS13B Golgi localization can be performed using image analysis software such as ImageJ, following this established methodology:

• Define two separate regions of interest (ROIs) for each cell:

  • Total cell ROI: Outlining the entire cell border to measure total VPS13B immunofluorescence

  • Golgi ROI: Outlining the GM130-positive Golgi structure to measure Golgi-associated VPS13B fluorescence

• Calculate the percentage of Golgi-associated VPS13B fluorescence compared to total cell VPS13B fluorescence intensity

• For statistical analysis, compare multiple cells (n > 30) using appropriate statistical tests with software such as GraphPad Prism

This approach has been validated for comparing wild-type and mutant VPS13B protein distribution and has proven valuable for classifying VPS13B missense variants .

How can VPS13B antibodies be used to investigate Cohen syndrome-associated mutations?

VPS13B antibodies serve as critical tools for functional characterization of Cohen syndrome-associated mutations through several complementary approaches:

• Subcellular localization analysis: Wild-type VPS13B protein localizes to the Golgi complex, co-localizing with Golgi matrix protein GM130. By expressing mutant VPS13B proteins (via site-directed mutagenesis) in cell culture models, researchers can use VPS13B antibodies to assess if disease-associated variants show altered Golgi localization .

• Quantitative cellular assays: A validated assay involves measuring the percentage of Golgi-associated VPS13B fluorescence compared to total cellular VPS13B. This approach has successfully demonstrated that the missense variant p.Arg237Pro shows significantly reduced Golgi enrichment compared to wild-type VPS13B, providing functional evidence for its pathogenicity .

• Protein interaction studies: VPS13B antibodies can immunoprecipitate the protein to investigate interactions with binding partners such as RAB6, Syntaxin 6 (STX6), Syntaxin 13 (STX13), and FAM177A, enabling assessment of whether mutations disrupt these critical interactions .

This combined approach provides crucial functional evidence to complement genetic data, supporting classification of variants according to ACMG guidelines .

What are the experimental considerations when studying VPS13B in neuronal models?

Investigating VPS13B in neuronal models presents specific challenges and considerations:

• Expression system selection:

  • Primary neurons: More physiologically relevant but challenging due to low transfection efficiency

  • iPSC-derived neurons: Allows study of patient-derived cells with endogenous mutations

  • Neuronal cell lines (SH-SY5Y, Neuro2a): Higher transfection efficiency but less physiologically relevant

• Visualization strategies for endogenous VPS13B:

  • Due to low endogenous expression levels, consider signal amplification methods such as tyramide signal amplification

  • Alternative approach: Express codon-optimized versions of VPS13B fused to fluorescent tags (GFP or Halo) to enhance visualization

• Functional readouts:

  • Golgi morphology assessment: VPS13B mutations may affect Golgi structure

  • Neurite outgrowth: VPS13B plays a role in neuron projection development

  • Trafficking dynamics: Assess trafficking between early and recycling endosomes

• Sex-specific considerations: Both mouse studies and human data suggest VPS13B plays a more prominent role in males than females, making it crucial to consider sex as a biological variable in experimental design .

What are the latest approaches for studying VPS13B at membrane contact sites?

Cutting-edge methodologies for investigating VPS13B at membrane contact sites include:

• Super-resolution microscopy techniques:

  • DNA-PAINT has been successfully employed to characterize VPS13B positioning relative to Golgi markers with nanometer precision

  • This approach revealed VPS13B's precise location at the cis-trans Golgi complex interface (approximately 28 nm from GM130)

• Multiplexed imaging:

  • Sequential imaging of VPS13B relative to different Golgi complex proteins

  • Implementation involves labeling proteins with antibodies conjugated to different single-stranded DNA docking sites, followed by sequential imaging using transient adapters

• Lipid transfer assays:

  • Testing VPS13B's ability to transfer specific phospholipids between artificial membranes

  • Assessing phosphatidylinositol 3-phosphate binding specificity

• Contact site visualization:

  • Investigating VPS13B's role in Golgi-lipid droplet contacts that associate with the endoplasmic reticulum

  • Analysis of co-localization with lipid droplet markers and ER markers at three-way junctions

How can inconsistent results with commercial VPS13B antibodies be addressed?

Inconsistent results with VPS13B antibodies can be addressed through a systematic approach:

• Antibody validation assessment:

  • Review validation data from manufacturers

  • Confirm antibody specificity against the specific VPS13B region of interest

  • Note that different antibodies may recognize different isoforms of VPS13B

• Alternative strategies for low endogenous expression:

  • Due to consistently reported low levels of endogenous protein expression, consider:

    • Signal amplification methods

    • Expression of tagged VPS13B constructs

    • Codon optimization to achieve robust expression of this large protein

• Protocol optimization:

  • Implement systematic troubleshooting by varying:

    • Fixation conditions

    • Antigen retrieval methods (compare TE buffer pH 9.0 vs. citrate buffer pH 6.0)

    • Antibody concentration

    • Incubation time and temperature

• Technical validation:

  • Include positive control tissues (human liver tissue, mouse brain tissue have demonstrated positive signal)

  • Incorporate negative controls (secondary antibody only, pre-immune serum)

How should discrepancies between VPS13B antibody results and genetic findings be interpreted?

When facing discrepancies between antibody-based results and genetic findings:

• Consider transcript variants:

  • At least five alternatively spliced VPS13B transcript variants have been observed

  • Confirm which isoform(s) your antibody detects (some antibodies detect two isoforms)

  • Reference transcript information (e.g., VPS13B transcript ENST00000357162.7, NM_152564.5, comprising 11,994 bp and encoding 3,997 amino acids)

• Evaluate epitope accessibility:

  • Some VPS13B mutations may affect protein folding without eliminating expression

  • Missense variants might alter epitope accessibility while preserving some protein function

  • Consider using multiple antibodies targeting different regions of VPS13B

• Functional validation approach:

  • Implement cellular detection assays measuring VPS13B subcellular distribution

  • Quantify Golgi enrichment as a functional readout

  • This approach successfully validated the pathogenicity of the missense variant p.Arg237Pro despite protein expression

• Integrated analysis:

  • Combine genetic findings with multiple functional approaches

  • Consider in silico analysis complemented by functional evidence

  • Recent findings emphasize "the need for combining genetic and functional testing of VPS13B missense variants to ensure accurate molecular diagnosis"

How are VPS13B antibodies being used to explore neurodevelopmental disorders beyond Cohen syndrome?

VPS13B antibodies are increasingly employed to investigate broader neurodevelopmental mechanisms:

• Comparative neurodevelopmental studies:

  • Investigating VPS13B's role in neuronal development and neuron projection formation

  • Exploring connections between VPS13B dysfunction and previously unreported neuroanatomical features such as hippocampal and cerebellar atrophy attributed to early-life neuronal loss

• iPSC-derived models:

  • Examining VPS13B function in patient-derived induced pluripotent stem cells differentiated into neurons

  • While still preliminary, these approaches aim to establish direct correlations between cellular phenotypes and in vivo features of the disease

• Intersection with related disorders:

  • Investigating the relationship between VPS13B and FAM177A, a Golgi-localized protein linked to a neurodevelopmental disorder with phenotypic similarities to Cohen syndrome

  • Studies show FAM177A exhibits a cellular phenotype similar to VPS13B, suggesting potential functional interaction

• Cross-family protein studies:

  • Comparing VPS13B with other VPS13 family members (VPS13A, VPS13C, VPS13D)

  • All family members are linked to rare neurodegenerative disorders: chorea-acanthocytosis (VPS13A), Cohen syndrome (VPS13B), early-onset Parkinson's disease (VPS13C), and ataxia/spastic paraplegia (VPS13D)

What methodological advances are improving VPS13B detection in complex biological samples?

Recent methodological innovations enhancing VPS13B detection include:

• Optimized immunoprecipitation protocols:

  • Improved techniques for pulling down VPS13B protein complexes from cell lysates

  • Enhanced ability to identify interaction partners (up to 100 potential binding partners have been identified)

• Antibody conjugation approaches:

  • Development of antibodies conjugated with single-stranded DNA docking sites for multiplexed imaging

  • This approach enables sequential visualization of VPS13B with multiple Golgi markers in the same sample

• Mouse model validation:

  • Mouse models demonstrate high clinical relevance, mirroring several features of Cohen syndrome patients

  • These models provide robust readouts for testing antibody specificity in vivo and validating VPS13B-associated phenotypes

• Codon optimization strategies:

  • Codon-optimized versions of full-length human VPS13B fused to tags like GFP or Halo help overcome expression challenges

  • This approach significantly enhances robust expression of this very large protein, similar to observations with other VPS13 family members