rpe65b Antibody

What is the primary function of RPE65 protein in visual systems?

RPE65 serves as a critical isomerohydrolase in the retinoid cycle involved in the regeneration of 11-cis-retinal, which is the chromophore of rod and cone opsins. It catalyzes the cleavage and isomerization of all-trans-retinyl fatty acid esters to 11-cis-retinol, which is subsequently oxidized by 11-cis retinol dehydrogenase to 11-cis-retinal for use as a visual chromophore. This process is essential for maintaining vision as it enables the proper functioning of the phototransduction cascade. RPE65 is indispensable for the production of 11-cis retinal for both rod and cone photoreceptors, making it central to visual function .

Which species-specific variants of RPE65 antibodies are available for research?

Several RPE65 antibody variants are available for cross-species research applications. The RPE65 monoclonal antibody clone E-5 (sc-390787) is reactive with mouse, rat, and human samples, making it versatile for comparative studies . Similarly, the rabbit monoclonal antibody EPR22579-44 demonstrates cross-reactivity with human, mouse, and rat samples, as validated through western blotting and immunohistochemistry techniques . For specialized zebrafish research, antibodies generated against specific zebrafish RPE65c peptides have been developed to study this ortholog's distinct localization and function . When selecting an antibody for your research, consider both the species reactivity and the specific applications for which the antibody has been validated.

What cellular localization pattern should be expected when using RPE65 antibodies?

When using RPE65 antibodies for localization studies, researchers should primarily expect staining in the retinal pigment epithelium (RPE) layer. Immunohistochemical analysis of human retina tissue using antibodies like EPR22579-44 demonstrates cytoplasmic staining specifically in pigment epithelium cells . The protein is predominantly membrane-associated due to palmitoylation by LRAT (lecithin retinol acyltransferase), which anchors it to the membrane—a modification critical for its enzymatic activity . In multiplex immunohistochemistry analyses, RPE65 staining is distinctly localized to the pigmented layer, contrasting with other retinal markers like rhodopsin (rod photoreceptor cells) and synapsin I (inner plexiform layer) . Species-specific variations in localization patterns may exist, particularly in zebrafish where RPE65c has been studied in Müller cells .

What are the optimal dilution ratios for different experimental applications of RPE65 antibodies?

The optimal dilution ratios for RPE65 antibodies vary significantly depending on the specific application and antibody clone. For western blot applications, the 401.8B11.3D9 clone performs optimally at 1-2 μg/ml , while the EPR22579-44 clone requires a 1:1000 dilution for detecting the expected 65 kDa band . For immunohistochemistry on paraffin-embedded tissues, recommended dilutions range from 1:250-1:500 for the 401.8B11.3D9 clone to 1:4000 for the EPR22579-44 clone . Immunofluorescence applications typically require higher antibody concentrations, with recommended dilutions of 1:50-1:200 for the 401.8B11.3D9 clone and 1:250 for frozen section staining with the EPR22579-44 clone . These ratios should be optimized for each experimental system, considering tissue type, fixation method, and detection system sensitivity.

What antigen retrieval methods are most effective for RPE65 immunohistochemistry?

Heat-mediated antigen retrieval methods have proven most effective for RPE65 immunohistochemistry. For the EPR22579-44 antibody, optimal results are achieved using Tris-EDTA buffer (pH 9.0) for 20 minutes prior to antibody incubation . When using the 401.8B11.3D9 clone on formalin-fixed paraffin-embedded (FFPE) tissues, sodium citrate buffer (10mM, pH 6.0) with 20 minutes of heat-induced antigen retrieval has been successfully employed . The specific retrieval method should be optimized based on tissue type, fixation duration, and antibody clone. For multiplex immunohistochemistry applications, consistency in antigen retrieval methods across all antibodies used in the panel is crucial to maintain tissue integrity and ensure comparable staining intensities.

How can researchers troubleshoot unexpected molecular weight variations of RPE65 in western blots?

When troubleshooting unexpected molecular weight variations in RPE65 western blots, researchers should consider several factors. The predicted molecular weight of RPE65 is approximately 60 kDa, but the observed band typically appears at 65 kDa . This discrepancy may be attributed to post-translational modifications, particularly palmitoylation, which is essential for membrane anchoring and enzymatic activity . Additionally, variations in sample preparation, reducing conditions, and gel concentration can affect migration patterns.

For definitive identification, researchers should:

• Include positive controls such as eye tissue lysates from the relevant species

• Use negative controls like PC-3 cell lysates, which do not express RPE65

• Verify expression patterns across different species if cross-reactivity is expected

• Consider protein denaturation conditions, as membrane proteins may migrate differently based on solubilization methods

The temporal expression pattern of RPE65 should also be considered, as Hamel et al. reported that in cultured bovine RPE cells, RPE65 protein levels become undetectable in western blots after day 14, despite detectable mRNA expression for at least 7 weeks .

How can RPE65 antibodies be effectively employed in multiplex immunofluorescence studies of retinal tissue?

For effective multiplex immunofluorescence studies using RPE65 antibodies, researchers should implement sequential staining protocols with careful optimization of antibody combinations. The RPE65 antibody EPR22579-44 has been successfully used in multiplex immunohistochemistry analyses of formalin/PFA-fixed paraffin-embedded human retina tissue at a dilution of 1:8000, in combination with antibodies against rhodopsin and synapsin I .

To achieve optimal results:

• Staining sequence is critical—begin with the weakest signal (often RPE65) and proceed to stronger signals

• Use tyramide signal amplification systems to enhance detection sensitivity and allow for antibody stripping between rounds

• Employ spectrally distinct fluorophores to minimize bleed-through (e.g., OpalTM520 for RPE65, OpalTM570 for rhodopsin, and OpalTM690 for synapsin I)

• Optimize antibody concentrations independently before combining in multiplex format

• Include appropriate controls for each antibody individually to verify specificity

• Use confocal microscopy with sequential scanning to minimize cross-channel interference

This approach allows for precise spatial localization of RPE65 in relation to other retinal markers, facilitating comprehensive analysis of retinal architecture and potential alterations in disease models .

What are the key considerations when using RPE65 antibodies for immunoprecipitation studies?

When conducting immunoprecipitation (IP) studies with RPE65 antibodies, several methodological considerations are crucial for success. The EPR22579-44 antibody has been validated for immunoprecipitation of RPE65 from mouse eyeball lysates at a dilution of 1:30, followed by western blot detection at 1:1000 . Similarly, the E-5 clone has been reported to be effective for IP applications .

Critical factors for successful RPE65 immunoprecipitation include:

• Starting material selection: Eye tissue lysates provide the most abundant source of RPE65, with approximately 0.35-0.5 mg of total protein recommended for efficient pulldown

• Lysis buffer composition: Membrane protein extraction requires detergent-based buffers that maintain protein conformation while efficiently solubilizing membrane components

• Antibody binding conditions: Pre-clearing lysates with control IgG and protein A/G beads helps reduce non-specific binding

• Washing stringency: Balance between removing non-specific interactions while preserving specific antibody-antigen complexes

• Detection method selection: HRP-conjugated VeriBlot secondary antibodies specifically designed for IP detection help minimize detection of denatured IP antibody heavy and light chains

• Controls: Include isotype control antibodies (e.g., rabbit monoclonal IgG) processed identically to evaluate non-specific binding

For studying protein-protein interactions involving RPE65, crosslinking approaches prior to immunoprecipitation may be necessary to capture transient interactions within the visual cycle machinery.

How do different antibody clones compare in their ability to detect RPE65 across various disease models?

Different RPE65 antibody clones exhibit varying capacities to detect alterations in RPE65 expression and localization across disease models. The 401.8B11.3D9 clone has been validated for analysis of FFPE human glioblastoma tissue sections , suggesting utility beyond normal retinal tissue. The EPR22579-44 clone demonstrates robust staining in normal human retina samples , while the E-5 clone has been reported to detect RPE65 in models of retinitis pigmentosa and Leber congenital amaurosis type 2 .

When selecting antibodies for disease model studies, consider:

• Epitope accessibility: Conformational changes or post-translational modifications in pathological states may mask certain epitopes

• Cross-reactivity profiles: Some clones may exhibit differential species cross-reactivity, important for translational studies

• Sensitivity threshold: Detection of reduced RPE65 expression in degenerative conditions requires antibodies with optimal signal-to-noise ratios

• Compatibility with tissue preservation methods: Disease tissues often undergo different fixation procedures that may affect antibody performance

A comparative analysis using multiple antibody clones in parallel can provide complementary information and validate findings across different recognition sites within the RPE65 protein, particularly important when studying mutations that may affect specific domains of the protein.

How do zebrafish RPE65 variants differ from mammalian orthologs in terms of antibody recognition and function?

Zebrafish present a unique system for studying RPE65 biology due to their distinct RPE65 variants. While mammals typically express a single RPE65 gene, zebrafish possess multiple orthologs including RPE65c, which has been specifically studied using custom antibodies generated against zebrafish-specific peptides . These zebrafish variants exhibit functional activity as isomerohydrolases, similar to their mammalian counterparts, but may have distinct cellular localization patterns.

When using antibodies for zebrafish RPE65 research:

• Standard mammalian-targeted RPE65 antibodies may have limited or unpredictable cross-reactivity with zebrafish variants

• Custom antibodies generated against specific zebrafish RPE65 peptides provide higher specificity for these orthologs

• Validation should include appropriate controls to confirm specificity, particularly when studying specific variants like RPE65c

• Consider differential expression patterns—zebrafish RPE65c has been localized to Müller cells , contrasting with the predominantly RPE localization in mammals

This evolutionary divergence in RPE65 variants makes zebrafish valuable models for comparative studies of visual cycle mechanisms, potentially informing our understanding of alternative isomerohydrolase pathways that could have therapeutic relevance.

What validation strategies are essential when applying RPE65 antibodies to novel model systems?

When applying RPE65 antibodies to novel model systems, comprehensive validation strategies are essential to ensure specific detection and accurate interpretation of results. For novel applications, researchers should:

• Perform western blot analysis comparing positive control tissues (eye lysates) with the novel sample type to confirm appropriate molecular weight detection (expected at approximately 65 kDa)

• Include genetic controls where possible (RPE65 knockout tissues, siRNA-treated samples, or overexpression systems)

• Validate across multiple applications (IHC, IF, WB) to confirm consistent detection patterns

• Test multiple antibody clones targeting different epitopes to confirm consistent staining patterns

• Perform peptide competition assays to demonstrate specificity of binding

• For non-ocular tissues or unexpected expression patterns, confirm findings with complementary techniques such as in situ hybridization or mRNA analysis

• When working with non-mammalian species, consider generating custom antibodies against species-specific RPE65 peptide sequences as demonstrated for zebrafish RPE65c

These validation approaches are particularly important when studying RPE65 expression in contexts beyond its well-established role in retinal pigment epithelium, such as potential expression in glioblastoma tissues or alternative cell types in non-mammalian models.

What specialized techniques are required for detecting low-abundance RPE65 expression in non-ocular tissues?

Detecting low-abundance RPE65 expression in non-ocular tissues requires specialized technical approaches to overcome sensitivity limitations. Researchers should consider:

• Signal amplification methods: Tyramide signal amplification can significantly enhance detection sensitivity for immunohistochemistry applications, allowing for the visualization of low-abundance proteins

• Super-resolution microscopy: Techniques such as STORM or STED microscopy can provide enhanced sensitivity and spatial resolution for detecting sparse protein expression

• Enhanced protein extraction: For western blot applications, membrane protein enrichment protocols using differential centrifugation or phase separation can concentrate RPE65 protein

• Proximity ligation assays: These provide single-molecule detection capability through rolling circle amplification, enhancing sensitivity for protein detection in situ

• Nested immunoprecipitation approaches: Sequential IP steps can enrich for low-abundance targets before detection

• Mass spectrometry validation: Targeted proteomics approaches can confirm RPE65 peptide presence in non-ocular samples with high sensitivity

When investigating low-abundance expression, researchers should be mindful that RPE65 levels in cultured cells may decrease over time, as observed in bovine RPE cells where protein becomes undetectable by western blot after 14 days in culture despite continued mRNA expression . This temporal regulation may necessitate careful timing of experiments when working with primary cell cultures.

How can researchers effectively study protein-protein interactions involving RPE65 using antibody-based approaches?

Studying protein-protein interactions involving RPE65 requires specialized antibody-based approaches that preserve native protein complexes. Effective methodological strategies include:

• Co-immunoprecipitation with optimized conditions:

  • Use membrane-compatible detergents that maintain protein interactions (digitonin, CHAPS)

  • Perform IP at 4°C with minimal manipulation to preserve complexes

  • Consider crosslinking approaches for transient interactions

  • Validate using antibodies against known interacting partners (e.g., LRAT)

• Proximity-based interaction assays:

  • Proximity ligation assays (PLA) provide in situ detection of proteins within 40nm proximity

  • FRET-based approaches using fluorescently-tagged antibodies can detect direct interactions

  • BioID or APEX2 proximity labeling coupled with antibody-based pulldown

• Blue native PAGE followed by western blotting:

  • Preserves native protein complexes through non-denaturing separation

  • Subsequent immunoblotting with RPE65 antibodies identifies complex components

  • Diagonal 2D electrophoresis (BN-PAGE followed by SDS-PAGE) identifies complex components

• Immunofluorescence co-localization studies:

  • High-resolution confocal or super-resolution microscopy

  • Quantitative co-localization analysis using appropriate statistical methods

  • Controls for random co-localization should be included

These approaches are particularly valuable for studying the interactions between RPE65 and other visual cycle components, such as LRAT, which palmitoylates RPE65 for membrane anchoring—a modification critical for its enzymatic activity .

What are the best approaches for quantifying RPE65 protein levels in comparative studies of retinal disease models?

For accurate quantification of RPE65 protein levels in comparative studies of retinal disease models, researchers should implement rigorous standardized protocols that account for technical and biological variables. Recommended approaches include:

• Quantitative western blotting:

  • Use fluorescent secondary antibodies for wider dynamic range and improved quantitative accuracy

  • Include loading controls appropriate for the sample type (GAPDH for total protein normalization)

  • Employ a standard curve of recombinant protein or positive control lysate dilutions

  • Present data as fold-change relative to control samples with appropriate statistical analysis

• ELISA-based quantification:

  • Consider use of validated ELISA systems or develop sandwich ELISA using RPE65 antibodies

  • Include standard curves with recombinant RPE65 protein

  • Normalize to total protein concentration in the sample

• Mass spectrometry-based quantification:

  • Targeted approaches using selected reaction monitoring (SRM) or parallel reaction monitoring (PRM)

  • Use isotopically labeled peptide standards for absolute quantification

  • Select peptides that uniquely identify RPE65 and are not subject to post-translational modifications

• Image-based quantification:

  • Standardize immunohistochemistry protocols including fixation, antigen retrieval, and detection

  • Use automated image analysis software with consistent thresholding parameters

  • Measure both intensity and area of expression

  • Include internal reference standards across batches

When comparing disease models, it is critical to match samples for age, sex, and genetic background, as these factors may influence RPE65 expression independently of the disease process. Additionally, researchers should be aware of diurnal variations in visual cycle protein expression and standardize tissue collection timing accordingly.