vps-18 Antibody

What is VPS-18 and what cellular functions does it perform?

VPS-18 (Vacuolar Protein Sorting 18) is a 973 amino acid peripheral membrane protein that plays crucial roles in vesicle-mediated protein trafficking to lysosomal compartments, including both endocytic membrane transport and autophagic pathways . It functions as a core component of the putative HOPS (homotypic fusion and protein sorting) and CORVET (class C core vacuole/endosome tethering) endosomal tethering complexes . These complexes are involved in Rab5-to-Rab7 endosome conversion and mediate tethering and docking events during SNARE-mediated membrane fusion . VPS-18 is predominantly localized to late endosomes and contains one clathrin repeat and one RING-type zinc finger . The protein exists in a large hetero-oligomeric complex with other vacuolar sorting proteins, including VPS11 and VPS16 . It is essential for proper endosome-lysosome and autophagosome-lysosome fusion events, making it critical for cellular homeostasis and waste disposal mechanisms .

Which applications are VPS-18 antibodies commonly used for in research?

VPS-18 antibodies are utilized across multiple research applications:

• Western Blotting (WB): For detecting VPS-18 protein expression levels in tissue and cell lysates, typically at the 100-110 kDa molecular weight range .

• Immunoprecipitation (IP): For isolating VPS-18 and its binding partners to study protein-protein interactions .

• Immunohistochemistry (IHC): For localizing VPS-18 in tissue sections, including brain, testis, and lung cancer tissues .

• Immunofluorescence (IF/ICC): For subcellular localization studies in cultured cells .

• ELISA: For quantitative detection of VPS-18 in various samples .

Each application requires specific antibody dilutions, with Western blot typically using 1:500-1:1000, IHC using 1:50-1:500, and IF/ICC using 1:200-1:800 dilutions .

What species reactivity do commercial VPS-18 antibodies demonstrate?

Commercial VPS-18 antibodies show varied species reactivity profiles. Most commonly, antibodies are validated for human and mouse samples . Some antibodies, like the VPS18 Antibody (237.1), are also validated for rat samples . When selecting an antibody for your research, it is crucial to verify species reactivity in the product documentation. For instance, Proteintech's 10901-1-AP antibody has been tested positively in human and mouse samples , while the VPS18 Antibody (237.1) from Santa Cruz Biotechnology detects mouse, rat, and human VPS18 . Species cross-reactivity is typically determined through sequence homology analysis and experimental validation in relevant tissue samples.

How should I optimize VPS-18 antibody concentration for Western blotting experiments?

For optimal Western blotting results with VPS-18 antibodies:

• Start with the manufacturer's recommended dilution range (typically 1:500-1:1000) , using a titration approach to determine the optimal concentration for your specific sample.

• Load appropriate protein amounts (20-50 μg of total protein) from whole cell lysates or tissue extracts. Brain tissue has shown good VPS-18 detection in multiple studies .

• Use fresh protein samples extracted with RIPA buffer containing protease inhibitors (1 mM PMSF and 1× proteinase inhibitor cocktail) to prevent degradation.

• When detecting VPS-18, expect bands at approximately 100-110 kDa , though variations may occur depending on post-translational modifications or splice variants.

• Include appropriate positive controls (brain tissue lysates work well) and negative controls (tissues with known low expression, such as lung) .

• For membrane blocking, use 5% non-fat milk or BSA in TBST and incubate overnight at 4°C with primary antibody for maximum sensitivity.

• Validate antibody specificity using knockout or knockdown samples when possible .

What are the recommended protocols for studying VPS-18 interactions with other HOPS complex proteins?

To investigate VPS-18 interactions with other HOPS complex components:

• Co-immunoprecipitation (Co-IP) is the primary method to detect protein-protein interactions. Use 0.5-4.0 μg of VPS-18 antibody for 1.0-3.0 mg of total protein lysate . Studies have successfully used this approach to detect interactions between VPS-18 and proteins like RAB11A .

• Choose appropriate lysis conditions: For membrane-associated complexes like HOPS, use buffers containing mild detergents (0.5-1% NP-40 or 0.5% Triton X-100) that preserve protein-protein interactions while solubilizing membrane proteins.

• Include appropriate controls (IgG control, input samples) to confirm specificity of detected interactions.

• For studying dynamic interactions, consider proximity ligation assays (PLA) or fluorescence resonance energy transfer (FRET) approaches.

• Mass spectrometry analysis of immunoprecipitated complexes can identify novel interaction partners.

• Validate key interactions through reciprocal co-IP experiments, pulling down with antibodies against suspected interacting partners and blotting for VPS-18.

• Consider the use of cross-linking agents before lysis to stabilize transient interactions within the HOPS complex.

What are the considerations for immunohistochemical detection of VPS-18 in tissue samples?

For successful IHC detection of VPS-18:

• Tissue preparation: Use 4% paraformaldehyde-fixed, paraffin-embedded tissues sectioned at 4-6 μm thickness.

• Antigen retrieval: VPS-18 detection typically requires antigen retrieval with TE buffer (pH 9.0) or alternatively with citrate buffer (pH 6.0) .

• Antibody dilution: Use VPS-18 antibodies at 1:50-1:500 dilution , optimizing the concentration for each tissue type.

• Incubation conditions: For primary antibodies, overnight incubation at 4°C often yields the best signal-to-noise ratio.

• Detection systems: HRP-conjugated secondary antibodies with DAB substrate work well for brightfield microscopy. For fluorescent detection, select secondary antibodies matching your primary antibody species.

• Positive controls: Include tissues known to express VPS-18, such as brain tissue, human testis tissue, or human lung cancer tissue .

• Counterstaining: Hematoxylin for brightfield or DAPI for fluorescence provides context for cellular localization.

• Image acquisition: Use appropriate magnification to detect both general distribution patterns (10-20×) and subcellular localization (40-63×).

How can VPS-18 antibodies be used to investigate autophagy pathway dysregulation?

VPS-18 antibodies provide valuable tools for studying autophagy dysregulation:

• Monitor autophagosome accumulation: VPS-18 deficiency leads to blockage of autophagosome clearance, resulting in accumulation of LC3-II and LC3-I proteins . Co-immunostaining with VPS-18 and LC3 antibodies can reveal correlation between VPS-18 levels and autophagosome accumulation.

• Assess autophagic flux: Use VPS-18 antibodies alongside other autophagy markers (p62, LC3) in the presence/absence of lysosomal inhibitors to determine whether VPS-18 alterations affect autophagosome formation or clearance .

• Quantify ubiquitinated protein accumulation: Loss of VPS-18 function leads to accumulation of ubiquitinated proteins and p62-positive inclusion bodies . Use VPS-18 antibodies in conjunction with anti-ubiquitin and anti-p62 antibodies to visualize this phenotype by co-immunofluorescence.

• Electron microscopy correlation: Combine immunogold labeling with VPS-18 antibodies and electron microscopy to precisely localize VPS-18 in relation to autophagic structures.

• Live cell imaging: Use fluorescently tagged VPS-18 constructs alongside LC3-RFP to monitor dynamics of autophagosome formation and clearance in real-time.

• Knockout/knockdown validation: Compare autophagy markers between VPS-18 knockout/knockdown and control samples to confirm the specific role of VPS-18 in autophagy regulation .

What is the role of VPS-18 in immune checkpoint regulation and how can it be studied?

Recent research has revealed that VPS-18 plays an unexpected role in immune checkpoint regulation:

• VPS-18 positively regulates PD-L1 (Programmed Death-Ligand 1) expression and confers resistance to immune checkpoint blockade therapy .

• Mechanistic studies show that VPS-18 interacts with PD-L1 during endosome recycling, promoting PD-L1 glycosylation and protein stability .

To investigate this role:

• Co-immunoprecipitation: Use VPS-18 antibodies to pull down associated proteins and probe for PD-L1 and related trafficking proteins like RAB11A .

• Immunofluorescence co-localization: Perform dual staining with VPS-18 and PD-L1 antibodies to visualize their spatial relationship in endosomal compartments.

• Flow cytometry: Compare PD-L1 surface expression levels in VPS-18-deficient versus control cells to quantify the impact of VPS-18 on PD-L1 presentation.

• In vivo tumor models: Compare tumor growth and response to immune checkpoint inhibitors in VPS-18 knockdown/knockout versus control tumors .

• T cell functional assays: Assess T cell infiltration, granzyme B expression, and IFN-γ production in tumors with modified VPS-18 expression to determine immunological consequences .

• Glycosylation analysis: Use glycosidase treatments and lectin blotting to evaluate how VPS-18 affects PD-L1 glycosylation patterns.

How can researchers investigate VPS-18's role in neurodegeneration using specific antibodies?

VPS-18 deficiency has been linked to neurodegeneration through disruption of vesicular trafficking pathways . To investigate this connection:

• Brain-specific conditional knockout models: Use VPS-18 antibodies to confirm deletion efficiency in conditional knockout mouse models by Western blot, IHC, and real-time PCR .

• Neuronal vesicle trafficking: Perform co-immunofluorescence with VPS-18 antibodies and markers for different endosomal compartments (Rab4, Rab7, Rab11, Eea1) to assess trafficking defects .

• Lysosomal function: Use VPS-18 antibodies alongside lysosomal markers (cathepsin D) to evaluate lysosomal integrity and function in neuronal cells .

• Neurodevelopmental analysis: Track VPS-18 expression patterns during neural development using IHC in brain sections from different developmental stages.

• Dendritic development: Examine Purkinje cell morphology in relation to VPS-18 expression, as VPS-18 is involved in dendrite development of these cells .

• Apoptosis assessment: Combine VPS-18 staining with apoptotic markers like cleaved caspase-3 to correlate VPS-18 deficiency with neuronal death .

• Notch signaling pathway: Analyze the relationship between VPS-18 and Notch signaling components, as VPS-18 deficiency affects cleaved Notch 1 levels .

What are common issues when using VPS-18 antibodies and how can they be resolved?

Researchers may encounter several challenges when working with VPS-18 antibodies:

• High background in Western blots:

  • Increase blocking time (2 hours at room temperature or overnight at 4°C)

  • Use alternative blocking agents (5% BSA instead of milk)

  • Include 0.1-0.3% Tween-20 in wash buffers

  • Increase number and duration of washes

  • Dilute primary antibody further based on manufacturer recommendations

• Weak or no signal detection:

  • Ensure VPS-18 is expressed in your sample (brain tissue is recommended as positive control)

  • Try different antibody concentrations

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

  • For IHC/IF, optimize antigen retrieval methods (try both TE buffer pH 9.0 and citrate buffer pH 6.0)

  • Use fresh samples and avoid repeated freeze-thaw cycles

• Multiple bands in Western blots:

  • VPS-18 may exhibit alternative splicing variants

  • Sample degradation may cause additional bands

  • Use freshly prepared samples with protease inhibitors

  • Verify band specificity using knockout/knockdown controls

• Poor reproducibility:

  • Standardize protocols including sample preparation, antibody dilutions, and incubation times

  • Aliquot antibodies to avoid repeated freeze-thaw cycles

  • Store antibodies according to manufacturer recommendations (-20°C for most antibodies)

How should researchers validate the specificity of VPS-18 antibodies in their experimental systems?

Proper validation of VPS-18 antibodies is crucial for reliable research outcomes:

• Genetic approaches:

  • Use samples from VPS-18 knockout or knockdown models as negative controls

  • Employ CRISPR/Cas9-mediated gene editing to create validation controls

  • Verify antibody specificity by detecting expected reduction in signal in these samples

• Recombinant protein controls:

  • Use purified VPS-18 recombinant proteins as positive controls in Western blots

  • Perform peptide competition assays with the immunizing peptide to confirm specificity

• Cross-validation:

  • Compare results using multiple antibodies targeting different epitopes of VPS-18

  • Verify that antibodies from different sources (e.g., Proteintech 10901-1-AP, Santa Cruz 237.1) show similar patterns

• Orthogonal techniques:

  • Confirm protein expression with mRNA expression data

  • Use mass spectrometry to verify the identity of the immunoprecipitated protein

• Expected molecular weight:

  • Confirm that the detected band appears at the expected molecular weight (100-110 kDa for VPS-18)

  • Be aware that post-translational modifications may alter the apparent molecular weight

• Cross-reactivity testing:

  • Test antibodies on samples from multiple species if cross-species reactivity is claimed

  • Include appropriate negative control tissues with low VPS-18 expression

What are the optimal storage and handling conditions for maintaining VPS-18 antibody activity?

To preserve VPS-18 antibody functionality:

• Storage temperature:

  • Store most antibodies at -20°C for long-term preservation

  • Avoid storing antibodies at 4°C for extended periods

• Buffer composition:

  • Most VPS-18 antibodies are supplied in PBS with 0.02% sodium azide and 50% glycerol at pH 7.3

  • Some contain 0.1% BSA as a stabilizer

• Aliquoting:

  • Upon receipt, divide antibodies into small working aliquots (10-20 μl) to avoid repeated freeze-thaw cycles

  • For small volumes (20 μl), aliquoting may be unnecessary for -20°C storage

• Freeze-thaw cycles:

  • Minimize freeze-thaw cycles as they can lead to antibody denaturation

  • Thaw aliquots on ice and return to storage promptly after use

• Working dilutions:

  • Prepare working dilutions fresh before each experiment

  • Do not store diluted antibodies for extended periods

• Contamination prevention:

  • Use sterile techniques when handling antibodies

  • Avoid touching the inside of tubes or caps

• Shipping considerations:

  • VPS-18 antibodies are typically shipped on wet ice

  • Upon receipt, transfer to appropriate long-term storage conditions immediately

Following these guidelines will help maintain antibody activity and ensure consistent experimental results over time.