Recombinant Mouse Probable ergosterol biosynthetic protein 28 (ORF11)

What is the primary cellular function of ERG28?

ERG28 plays a critical role in sterol biosynthesis pathways. Research indicates that ERG28 functions as a non-catalytic scaffolding protein that facilitates cholesterol synthesis in mammalian cells . It acts by interacting with multiple enzymes involved in the sterol biosynthetic pathway, particularly members of the C4-demethylation complex including NSDHL and SC4MOL . Knockout studies have demonstrated that ERG28-deficient cells show a 60-75% reduction in the rate of cholesterol synthesis and reduced total cholesterol levels in sterol-depleted environments, confirming its essential role in maintaining efficient sterol production . Additionally, ERG28 appears to influence SREBP-2 processing, further impacting the regulation of multiple cholesterol synthesis genes .

How is the expression of ERG28 regulated?

ERG28 expression is primarily regulated at the transcriptional level by sterol regulatory element-binding protein 2 (SREBP-2), similar to most cholesterol synthesis enzymes . Sterol-responsive elements (SREs) have been identified in the ERG28 promoter region, with binding sites for transcription factors including SREBP-2, Sp1, and NF-Y .

Quantitative analysis using luciferase reporter assays has demonstrated that the proximal promoter region (-290/+80) containing these elements is sufficient for sterol-regulated expression. Mutations in these binding sites, particularly the SREs, significantly reduce promoter activity, confirming their functional importance . Under sterol-depleted conditions, SREBP-2 processing increases, leading to enhanced ERG28 expression.

What are the optimal conditions for reconstitution and storage of recombinant Mouse ERG28 protein?

For optimal handling of recombinant Mouse ERG28 protein, follow this detailed protocol:

Reconstitution Protocol:

• Centrifuge the vial briefly before opening to collect contents at the bottom

• Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 5-50% (optimal: 50%)

• Aliquot for long-term storage

Storage Conditions:

• Store lyophilized powder at -20°C/-80°C upon receipt

• Store reconstituted working aliquots at 4°C for up to one week

• For long-term storage of reconstituted protein, store aliquots at -20°C/-80°C

• Avoid repeated freeze-thaw cycles as they significantly degrade protein activity

Buffer Conditions:
The protein is typically provided in Tris/PBS-based buffer with 6% Trehalose, pH 8.0 . For functional studies, researchers should consider that the native environment of ERG28 is the ER membrane, so experimental conditions may need to account for this membranous nature.

What protein-protein interactions have been identified for ERG28, and how can these be studied?

ERG28 participates in several key protein-protein interactions that appear crucial for its function in sterol biosynthesis. Confirmed interactions include:

Recommended Methodologies for Studying Interactions:

• NanoBiT® Complementation Assay: This split luciferase system has been successfully employed to detect ERG28 interactions. Clone your gene of interest with either large (LgBiT) or small (SmBiT) luciferase fragments in both N- and C-terminal configurations to account for potential steric hindrance .

• Co-immunoprecipitation: For endogenous interactions, use anti-ERG28 antibodies to pull down protein complexes, followed by mass spectrometry or Western blotting for potential interacting partners.

• Proximity Labeling: BioID or APEX2 fusions with ERG28 can identify proximal proteins in the native cellular environment, particularly valuable given its membrane association.

• Membrane Yeast Two-Hybrid: Given ERG28's membrane localization, conventional Y2H systems may yield false negatives; consider membrane-specialized Y2H systems.

When studying ERG28 interactions, it's critical to maintain native membrane environments or suitable detergents that preserve protein conformation.

What phenotypic changes occur in ERG28 knockout models, and what are the implications for cholesterol metabolism research?

ERG28 knockout models exhibit several significant phenotypic alterations with important implications for cholesterol metabolism research:

Cellular Phenotypes:

• 60-75% reduction in cholesterol synthesis rate

• Reduced total cholesterol levels specifically in sterol-depleted environments

• Impaired SREBP-2 processing

• Downregulation of multiple cholesterol synthesis genes

Experimental Design Considerations:
When utilizing ERG28 knockout models, researchers should implement a comprehensive approach that includes:

• Metabolic Flux Analysis: Radiolabeled precursors (e.g., [14C]-acetate) should be employed to quantify synthesis rates across the sterol pathway, identifying potential rate-limiting steps or accumulated intermediates.

• Sterol Profiling: Liquid chromatography-mass spectrometry (LC-MS) analysis is recommended to quantify changes in the complete sterol profile, not just end-product cholesterol, as accumulation of intermediates may occur.

• Transcriptional Impact Assessment: RNA-seq or targeted qPCR of sterol biosynthetic genes will reveal secondary effects of ERG28 knockout on the sterol regulatory network.

• Complementation Studies: Re-expression of wild-type ERG28 should rescue the phenotype, confirming specificity. Consider domain-specific mutants to map functional regions.

• Stress Response Analysis: Assess cell viability under various stressors, particularly those affecting ER function, as ERG28's ER localization suggests potential roles in ER homeostasis beyond sterol synthesis.

These models provide valuable tools for investigating the non-enzymatic regulation of sterol biosynthesis and may identify novel intervention points for disorders of cholesterol metabolism.

How does ERG28 function differ between yeast and mammalian systems?

ERG28 shows interesting evolutionary conservation yet functional divergence between yeast and mammalian systems:

When designing comparative studies between yeast and mammalian ERG28, researchers should consider:

• The different end products of the pathway (ergosterol vs. cholesterol)

• Divergent regulatory mechanisms controlling ERG28 expression

• Potential differences in protein complex assembly

• The possibility of additional mammalian-specific functions not present in yeast

Cross-species complementation experiments (expressing mammalian ERG28 in yeast erg28Δ strains and vice versa) can provide valuable insights into conserved functional domains and species-specific adaptations.

What experimental approaches can be used to study ERG28 promoter regulation?

Based on recent studies, the following comprehensive approaches are recommended for investigating ERG28 promoter regulation:

Promoter Mapping and Analysis:

• Luciferase Reporter Assays: Generate nested deletion constructs of the ERG28 promoter (e.g., -1000/+80, -500/+80, -290/+80, -50/+80, 0/+80) fused to a luciferase reporter to identify key regulatory regions .

• Site-Directed Mutagenesis: Introduce targeted mutations in predicted binding sites (SREs, Sp1, NF-Y) to evaluate their functional importance. Predicted SREs can be mutated to xAACAxAAGx, Sp1 sites to TTTAAA, and NF-Y sites to AATTCC .

• Chromatin Immunoprecipitation (ChIP): Perform ChIP assays with antibodies against SREBP-2, Sp1, and NF-Y to confirm direct binding to the ERG28 promoter in vivo.

Computational Prediction Methods:
For identifying potential regulatory elements in the ERG28 promoter, employ:

• Find Individual Motif Occurrences program for SRE prediction

• ConSite for Sp1 and NF-Y binding site prediction

• JASPAR or other current databases for additional transcription factor binding sites

Sterol Response Testing:
Evaluate promoter activity under various conditions:

• Sterol depletion (medium with lipoprotein-deficient serum plus statin)

• Sterol loading (medium with excess cholesterol/25-hydroxycholesterol)

• In the presence of SREBP-2 overexpression or knockdown

This integrated approach will provide a comprehensive understanding of ERG28 transcriptional regulation and its responsiveness to cellular sterol status.

What are the key considerations for designing antibodies against Mouse ERG28?

When designing antibodies against Mouse ERG28, researchers should consider several critical factors to ensure specificity and utility across different applications:

Epitope Selection Considerations:

• Membrane Topology Analysis: As a polytopic membrane protein, ERG28 has limited exposed regions. Perform hydrophobicity analysis to identify extramembrane loops or termini.

• Species Conservation: The high conservation between mouse and human ERG28 (~87% identity) allows for potential cross-reactivity, which may be desirable or undesirable depending on your experimental needs.

• Post-translational Modifications: Check for predicted glycosylation, phosphorylation, or other modifications that might interfere with antibody recognition.

Recommended Immunogen Strategies:

• Synthetic Peptides: Target unique extramembrane domains (preferably 15-20 amino acids). The C-terminal region (LRYLEAEPVSRQKKRN) represents a potentially immunogenic sequence.

• Recombinant Protein Fragments: Express soluble domains rather than the full transmembrane protein.

• Whole Protein Immunization: Use the purified recombinant His-tagged protein , recognizing that antibodies will predominantly recognize extramembrane domains.

Validation Experiments:

• Western blotting against recombinant protein and endogenous ERG28 (predicted MW: 15.9 kDa)

• Immunoprecipitation followed by mass spectrometry

• Immunofluorescence with subcellular markers (especially ER markers)

• Reduced or absent signal in ERG28 knockout cells as negative control

Due to potential cross-reactivity issues, extensive validation is essential to ensure antibody specificity for Mouse ERG28, particularly in tissues or cell lines where multiple ERG28 family members may be expressed.

How can researchers effectively study the role of ERG28 in cholesterol synthesis pathways?

To comprehensively investigate ERG28's role in cholesterol synthesis, a multi-faceted approach incorporating various techniques is recommended:

Genetic Manipulation Strategies:

• CRISPR/Cas9 Knockout: Generate complete ERG28 knockout cell lines as demonstrated in previous research with Huh7 cells .

• Inducible Knockdown: Employ doxycycline-inducible shRNA systems to create temporal control over ERG28 depletion.

• Domain-Specific Mutations: Introduce targeted mutations in predicted functional domains to identify critical regions without complete protein elimination.

• Rescue Experiments: Re-express wild-type or mutant ERG28 in knockout backgrounds to confirm specificity and map functional domains.

Metabolic Analysis Approaches:

• Radiolabeled Metabolic Flux Assays: Use [14C]-acetate or [3H]-mevalonate to track cholesterol synthesis rates, as previously employed to demonstrate 60-75% reduction in synthesis in ERG28 knockout cells .

• Mass Spectrometry Sterol Profiling: Quantify complete sterol profiles to identify specific steps affected by ERG28 manipulation.

• Lipidomics Analysis: Broader lipid profiling may reveal unexpected roles of ERG28 in other lipid metabolic pathways.

Molecular Interaction Studies:

• Proximity Labeling: BioID or APEX2 fusions can identify the complete interactome of ERG28 in intact cells.

• Co-immunoprecipitation: Paired with mass spectrometry for unbiased interaction identification.

• Split Luciferase Complementation Assays: As previously applied to demonstrate interactions with NSDHL and SC4MOL .

Functional Readouts:

• SREBP-2 Processing Analysis: Western blotting for precursor and mature SREBP-2 forms.

• Transcriptional Profiling: RNA-seq to identify global effects on gene expression.

• Membrane Fluidity Measurements: Fluorescence anisotropy to assess functional consequences of altered sterol composition.

This integrated approach will provide comprehensive insights into ERG28's role in cholesterol biosynthesis beyond current understanding.

What expression systems are most effective for producing functional recombinant Mouse ERG28?

The choice of expression system significantly impacts the yield, folding, and functionality of recombinant Mouse ERG28. Based on available data and protein characteristics, here are comparative recommendations:

Key Considerations for Functional ERG28 Production:

• Membrane Environment: As ERG28 is a membrane protein, consider adding lipids during purification or reconstituting into nanodiscs/liposomes post-purification.

• Purification Strategy:

  • For His-tagged constructs, use IMAC with careful optimization of imidazole concentrations

  • Consider mild detergents (DDM, LMNG) for extraction while maintaining native conformation

  • Implement size exclusion chromatography as a final polishing step

• Functionality Assessment:

  • Circular dichroism to confirm proper secondary structure

  • Binding assays with known interaction partners (NSDHL, SC4MOL)

  • Reconstitution into liposomes followed by functional assays

For most research applications requiring functional protein, mammalian expression systems (particularly HEK293T cells) represent the optimal balance of native-like processing and reasonable yield.

What is the potential role of ERG28 in disease states, particularly cancer?

Recent research suggests ERG28 may have significant implications in various disease states, particularly cancer:

ERG28 Expression in Cancer:
Transcriptomic data indicates ERG28 is highly expressed in several cancer cell lines, notably those derived from colon, leukocyte, and pancreatic tissues . In pancreatic cancers specifically, ERG28 has been observed to demonstrate plasma membrane localization, differing from its typical ER localization in normal cells .

Potential Mechanisms of Involvement:

• Altered Cholesterol Metabolism: Cancer cells often exhibit dysregulated cholesterol metabolism to support rapid proliferation. As ERG28 facilitates cholesterol synthesis, its upregulation may support the increased sterol demands of cancer cells.

• Membrane Organization: Changes in ERG28 localization (ER to plasma membrane) in cancer cells suggest potential roles in modifying membrane composition or signaling platform organization.

• Interaction with Cancer-Related Pathways: ERG28's influence on SREBP-2 processing may have broader implications for lipid metabolism reprogramming in cancer.

Research Approaches to Investigate ERG28 in Disease:

• Expression Correlation Analysis: Analyze ERG28 expression across cancer databases (TCGA, CCLE) and correlate with patient outcomes and known cancer pathways.

• Functional Studies in Cancer Models: Perform ERG28 knockdown/overexpression in cancer cell lines and assess impacts on proliferation, migration, and response to therapy.

• Metabolic Dependency Testing: Determine if ERG28 inhibition sensitizes cancer cells to metabolic stress or therapeutic agents.

• In vivo Models: Generate conditional ERG28 knockout mouse models to assess its role in cancer initiation and progression in relevant tissues.

This emerging area warrants further investigation, as targeting cholesterol metabolism through non-enzymatic facilitators like ERG28 may represent a novel therapeutic approach.

How does ERG28 interact with the broader cellular stress response network?

The relationship between ERG28 and cellular stress response pathways represents an emerging area of investigation with significant implications:

Potential Stress Response Connections:

• ER Stress and Unfolded Protein Response (UPR): As an ER-resident protein involved in sterol homeostasis, ERG28 likely interfaces with ER stress pathways. Changes in membrane lipid composition due to ERG28 dysfunction could trigger or modify UPR signaling.

• Oxidative Stress: The sterol biosynthetic pathway involves numerous redox reactions. ERG28's role in facilitating this pathway may indirectly influence cellular redox balance.

• Nutrient Sensing: SREBP-2, which regulates ERG28, is responsive to cellular energy status through AMPK signaling. This suggests ERG28 may be part of the broader cellular nutrient sensing network.

Experimental Approaches to Investigate These Connections:

• Stress Response Profiling in ERG28-Manipulated Cells:

  • Monitor UPR markers (CHOP, BiP, XBP1 splicing) in ERG28 knockout vs. wild-type cells

  • Assess oxidative stress markers (ROS levels, glutathione status)

  • Measure activation of stress-responsive kinases (JNK, p38 MAPK)

• Stress Challenge Experiments:

  • Determine if ERG28 knockout/overexpression alters sensitivity to ER stress inducers (tunicamycin, thapsigargin)

  • Test responses to oxidative stressors (H₂O₂, paraquat)

  • Assess adaptation to nutrient limitation (glucose, amino acid starvation)

• Signaling Pathway Intersection:

  • Investigate if ERG28 is post-translationally modified during stress responses

  • Determine if stress-responsive transcription factors (ATF4, ATF6, Nrf2) regulate ERG28

  • Map ERG28-dependent changes in lipid raft composition and associated signaling

This research direction could reveal novel functions of ERG28 beyond its established role in sterol biosynthesis and potentially identify new therapeutic approaches targeting the intersection of lipid metabolism and stress responses.

What are the comparative differences in ERG28 function across different tissues and developmental stages?

Understanding the tissue-specific and developmental variations in ERG28 function represents an important frontier in research:

Tissue Expression Patterns:
Transcriptomic data indicates that ERG28 is expressed across most human tissues, with notably high expression in the testis . This differential expression pattern suggests potential tissue-specific functions that remain to be fully characterized.

Developmental Considerations:
The role of ERG28 during development has not been extensively studied, but several hypotheses warrant investigation:

• Embryonic Development: Cholesterol is critical for embryonic development, particularly for hedgehog signaling pathway function. ERG28's facilitation of cholesterol synthesis may have developmental implications.

• Neurological Development: The brain is particularly dependent on proper cholesterol homeostasis. ERG28's role in neural development and function represents an important research direction.

• Reproductive System: The notably high expression in testis suggests potential specialized functions in reproductive tissues.

Methodological Approaches for Comparative Studies:

• Tissue-Specific Knockouts: Generate conditional ERG28 knockout models using tissue-specific Cre drivers to assess functional roles across different systems.

• Developmental Expression Profiling:

  • Perform immunohistochemistry or in situ hybridization across developmental stages

  • Utilize single-cell RNA-seq data from developmental studies to track ERG28 expression patterns

• Tissue-Specific Interactome Analysis:

  • Compare ERG28 protein interaction partners across different tissues

  • Identify tissue-specific post-translational modifications that might regulate function

• Organoid Models:

  • Utilize tissue-specific organoids with ERG28 manipulation to assess functional impact

  • Compare phenotypes across different tissue organoids (brain, liver, intestine)

This comparative approach will provide important insights into how a broadly expressed protein like ERG28 may serve specialized functions across different tissues and developmental contexts, potentially revealing new therapeutic opportunities for tissue-specific targeting.

What are the optimal storage and handling procedures for maintaining ERG28 protein stability?

For researchers working with recombinant Mouse ERG28 protein, proper storage and handling are critical for maintaining functional integrity. Follow these detailed protocols based on empirical evidence:

Storage Recommendations:

Reconstitution Protocol:

• Centrifuge the vial briefly before opening to bring contents to the bottom

• Reconstitute in deionized sterile water to 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 50%

• Aliquot into single-use volumes (10-50 μL recommended)

• Flash freeze in liquid nitrogen before transferring to -80°C storage

Handling Best Practices:

• Always keep the protein on ice when working at the bench

• Avoid repeated pipetting or vortexing that may cause denaturation

• If dilution is needed, use pre-chilled buffers

• Consider adding protease inhibitors for extended handling periods

• Monitor protein stability over time using SDS-PAGE

Stability Monitoring:
Researchers should periodically verify protein integrity through:

• SDS-PAGE to confirm absence of degradation

• Functional assays if available (e.g., interaction studies with known partners)

• Circular dichroism to assess secondary structure maintenance

Following these protocols will maximize the shelf-life and experimental utility of recombinant ERG28 protein preparations.

What experimental controls are essential when studying ERG28 function in cholesterol biosynthesis?

When investigating ERG28's role in cholesterol biosynthesis, implementing appropriate experimental controls is critical for obtaining reliable and interpretable results:

Essential Negative Controls:

• ERG28 Knockout/Knockdown Cells:

  • Complete knockout cell lines (CRISPR/Cas9-generated)

  • Inducible knockdown systems for temporal control

  • Scrambled/non-targeting siRNA controls for RNAi experiments

• Inactive Protein Controls:

  • Expression of mutant ERG28 lacking critical functional domains

  • Heat-inactivated recombinant protein for in vitro studies

  • Unrelated membrane protein of similar size/topology as specificity control

Essential Positive Controls:

• Rescue Experiments:

  • Re-expression of wild-type ERG28 in knockout backgrounds

  • Complementation with orthologous ERG28 from other species to assess functional conservation

• Pathway Validation:

  • Known modulators of cholesterol synthesis (statins, oxysterols)

  • SREBP-2 activators or inhibitors as pathway-level controls

Experimental Condition Controls:

• Sterol Status Manipulation:

  • Sterol-depleted conditions (lipoprotein-deficient serum plus statin)

  • Sterol-replete conditions (cholesterol/25-hydroxycholesterol supplementation)

  • Time-course experiments to distinguish acute vs. chronic effects

• Metabolic Labeling Controls:

  • Parallel labeling with multiple precursors ([14C]-acetate, [3H]-mevalonate)

  • Non-sterol lipid synthesis markers to assess pathway specificity

  • Metabolic inhibitor controls targeting specific pathway steps

Technical Validation Controls:

• Antibody Validation:

  • Preabsorption with recombinant protein

  • Multiple antibodies targeting different epitopes

  • Knockout/knockdown samples as negative controls

• Subcellular Fractionation Quality Controls:

  • Organelle-specific markers (Calnexin for ER, GM130 for Golgi)

  • Assessment of cross-contamination between fractions

  • Parallel immunofluorescence validation of localization

Implementing this comprehensive control strategy will ensure robust and reproducible data when investigating ERG28 function in cholesterol biosynthesis.