EMC4 Antibody

What is EMC4 and what is its biological significance?

EMC4 (ER membrane protein complex subunit 4) is a critical component of the endoplasmic reticulum membrane protein complex (EMC). This protein plays an essential role in the energy-independent insertion of newly synthesized membrane proteins into the endoplasmic reticulum membranes . The canonical human EMC4 protein consists of 183 amino acid residues with a molecular weight of approximately 20.1 kDa . Its predominant subcellular localization is in the endoplasmic reticulum, where it performs its membrane insertion functions. EMC4 is also known by several synonyms including TMEM85, HSPC184, and PIG17 (cell proliferation-inducing gene 17 protein) .

EMC4 preferentially accommodates proteins with transmembrane domains that are weakly hydrophobic or contain destabilizing features such as charged and aromatic residues . It is involved in both cotranslational insertion of multi-pass membrane proteins (where stop-transfer membrane-anchor sequences become ER membrane spanning helices) and post-translational insertion of tail-anchored proteins in ER membranes . Through these functions, EMC4 indirectly influences numerous cellular processes.

Which tissues predominantly express EMC4?

EMC4 expression has been documented across various human tissues. According to the available data, EMC4 is notably expressed in the colon, cerebral cortex, cerebellum, caudate, and adrenal gland . This expression pattern suggests EMC4's functional importance in these tissue types, though its presence is not strictly limited to these regions. Due to its role in fundamental membrane protein insertion processes, EMC4 likely has expression across many cell types where active membrane protein synthesis occurs.

What are the validated applications for EMC4 antibodies?

EMC4 antibodies have been validated for multiple experimental applications based on the search results. The primary validated applications include:

• Western Blotting (WB): For detecting EMC4 in protein lysates and assessing expression levels

• Immunohistochemistry (IHC-P): For visualizing EMC4 distribution in formalin-fixed, paraffin-embedded tissue sections

• Immunocytochemistry/Immunofluorescence (ICC-IF): For cellular localization studies

• Immunoprecipitation (IP): For isolating EMC4 protein complexes and studying protein-protein interactions

• ELISA: For quantitative detection of EMC4

Different antibody clones may have varying performance across these applications, so researchers should select antibodies validated specifically for their intended experimental approach .

How should I optimize Western blot protocols for detecting EMC4?

When optimizing Western blot protocols for EMC4 detection, consider the following methodological recommendations:

• Sample preparation: Due to EMC4's membrane localization, use lysis buffers containing mild detergents (such as 1% NP-40 or 0.5% Triton X-100) to efficiently extract membrane-associated proteins.

• Protein loading: Load 20-30 μg of total protein per lane for cell lysates; higher amounts may be needed for tissue homogenates with lower EMC4 expression.

• Transfer conditions: Use PVDF membranes for optimal protein binding and transfer at 100V for 60-90 minutes or overnight at 30V to ensure complete transfer of membrane proteins.

• Blocking: Use 5% non-fat dry milk or BSA in TBST for 1 hour at room temperature to minimize background.

• Antibody dilution: Primary EMC4 antibodies should typically be used at dilutions between 1:1000 to 1:5000 depending on the specific antibody concentration and sensitivity.

• Detection method: HRP-conjugated secondary antibodies with ECL substrates are suitable, but for low-abundance detection, consider more sensitive detection systems.

• Expected band size: Look for a band at approximately 20 kDa, which corresponds to the predicted molecular weight of EMC4 .

If multiple bands appear, validate specificity using positive controls and EMC4 knockdown/knockout samples to confirm the identity of the target band.

How does EMC4 interact with other EMC complex subunits?

EMC4 functions as part of the multi-subunit endoplasmic reticulum membrane protein complex (EMC), which consists of ten subunits in mammals. Within this complex, EMC4 interacts with other EMC subunits to form a functional membrane protein insertion machinery. While the search results don't provide detailed information on the specific interactions between EMC4 and other EMC subunits, research has established that EMC4 works in concert with EMC1, EMC6, and EMC7 during certain cellular processes, such as SV40 virus infection .

To study these interactions experimentally, researchers can:

• Perform co-immunoprecipitation experiments using anti-EMC4 antibodies to pull down the complex and identify interacting partners

• Use proximity labeling approaches such as BioID (as described with Myc-BioID2-EMC4)

• Conduct yeast two-hybrid screens or mammalian two-hybrid assays to identify direct protein-protein interactions

• Employ FRET/BRET approaches to visualize interactions in living cells

The interdependent nature of EMC subunits means that depletion of one subunit (like EMC4) often affects the stability and function of the entire complex.

What is known about EMC4's interaction with Rab7 and its functional significance?

EMC4 has been identified to interact with the late endosome-associated protein Rab7 GTPase. This interaction appears to be selective for active forms of Rab7 that associate with late endosomes. Research has demonstrated that:

• BioID proximity labeling experiments show EMC4 can biotinylate Rab7 but not the early endosome marker Rab5, indicating specific proximity to Rab7 .

• Immunoprecipitation studies confirm that EMC4 can co-precipitate with Rab7, demonstrating a physical interaction between these proteins .

• EMC4 selectively interacts with wild-type Rab7 and constitutively-active Rab7 (Q67L mutant), both of which associate with late endosomes, but not with the dominant-negative Rab7 (N125I mutant) that fails to associate with late endosomes .

This interaction appears functionally significant in viral infection pathways, particularly for SV40 virus. EMC4 has been shown to promote SV40 infection by facilitating late endosome-to-ER targeting of the virus . This suggests EMC4 may function as a molecular tether between late endosomes and the ER, potentially creating membrane contact sites that facilitate material transfer between these organelles.

To study this interaction experimentally, researchers can employ:

• Co-immunoprecipitation with anti-EMC4 antibodies

• Proximity labeling techniques like BioID

• Fluorescence microscopy to visualize co-localization

• Mutational analysis to identify interaction domains

How does EMC4 contribute to SV40 virus infection pathways?

EMC4 plays a significant role in Simian Virus 40 (SV40) infection by facilitating the virus's entry pathway. Research has demonstrated that:

• siRNA-mediated knockdown of EMC4 blocks SV40 infection, and expression of siRNA-resistant EMC4-FLAG can fully restore virus infection in EMC4-depleted cells, establishing EMC4's essential role in this process .

• EMC4 acts alongside other EMC subunits (EMC1, EMC6, and EMC7) to promote SV40 infection .

• Mechanistically, EMC4 and EMC7 appear to function as molecular tethers that support late endosome (LE) to ER targeting of the virus .

• EMC4 physically interacts with Rab7, specifically binding to the active (GTP-bound) form that associates with late endosomes, suggesting EMC4 may help establish membrane contact sites between LE and ER compartments .

This pathway represents a unique function of EMC4 that extends beyond its canonical role in membrane protein insertion. For researchers studying viral entry mechanisms or EMC complex functions, this represents an important experimental system where EMC4 function can be assessed.

What methods can be used to study EMC4's role in membrane protein insertion pathways?

To investigate EMC4's function in membrane protein insertion pathways, researchers can employ several methodological approaches:

• Genetic manipulation techniques:

  • siRNA or shRNA-mediated knockdown of EMC4 followed by assessment of membrane protein insertion efficiency

  • CRISPR-Cas9 gene editing to create EMC4 knockout cell lines

  • Rescue experiments using siRNA-resistant EMC4 constructs to confirm specificity

• Reporter systems for membrane protein insertion:

  • Split GFP complementation assays where fluorescence occurs only upon proper membrane insertion

  • Glycosylation reporter assays that monitor ER lumen translocation

  • Protease protection assays to determine membrane topology

• Biochemical assays:

  • In vitro translation/translocation assays using microsomes or reconstituted systems

  • Photocrosslinking to capture EMC4 interactions with substrate proteins during insertion

  • Selective permeabilization assays to determine protein topology

• Imaging approaches:

  • Live-cell imaging with fluorescently tagged EMC4 and substrate proteins

  • Super-resolution microscopy to visualize EMC4 distribution and dynamics at the ER membrane

  • FRET-based assays to detect proximity between EMC4 and client proteins

When designing these experiments, researchers should consider using client proteins known to depend on the EMC complex, particularly those with transmembrane domains that are weakly hydrophobic or contain charged/aromatic residues, as these are preferentially accommodated by EMC4 .

How can I validate the specificity of EMC4 antibodies?

Validating antibody specificity is crucial for reliable research outcomes. For EMC4 antibodies, consider implementing these validation strategies:

• Genetic approaches:

  • Test antibody reactivity in EMC4 knockout or knockdown samples (using CRISPR-Cas9 or siRNA) compared to controls

  • Perform rescue experiments by reintroducing EMC4 to knockout cells and confirming restored antibody signal

• Expression systems:

  • Use recombinant EMC4 protein as a positive control

  • Test antibody against overexpressed tagged EMC4 (e.g., FLAG-tagged or GFP-tagged) and confirm co-localization with the tag-specific antibody

• Immunoprecipitation validation:

  • Perform immunoprecipitation with the EMC4 antibody followed by mass spectrometry to confirm EMC4 enrichment

  • Conduct reciprocal co-immunoprecipitation with antibodies against known EMC4 interactors

• Multiple antibody comparison:

  • Use multiple antibodies targeting different EMC4 epitopes and confirm consistent patterns

  • Compare polyclonal and monoclonal antibodies (e.g., rabbit polyclonal anti-EMC4 vs. rabbit recombinant monoclonal EMC4 antibodies)

• Application-specific controls:

  • For IHC/ICC: Include absorption controls by pre-incubating antibody with recombinant EMC4

  • For Western blotting: Run predicted molecular weight markers and look for the expected 20.1 kDa band

What are common pitfalls when working with EMC4 antibodies and how can they be addressed?

When working with EMC4 antibodies, researchers may encounter several technical challenges. Here are common pitfalls and their solutions:

• Weak or absent signal in Western blots:

  • Ensure proper protein extraction of membrane proteins using detergent-containing lysis buffers

  • Optimize antibody concentration and incubation conditions (try overnight at 4°C)

  • Consider enhanced detection systems for low-abundance proteins

  • Test different blocking agents (milk vs. BSA) as some antibodies perform better with specific blockers

• High background in immunostaining:

  • Increase washing steps (number and duration)

  • Optimize antibody dilution (typically start with manufacturer recommendations)

  • Use alternative blocking solutions (try 5% normal serum from the species of secondary antibody)

  • Consider antigen retrieval optimization for IHC applications

• Cross-reactivity issues:

  • Validate antibody specificity in knockout/knockdown systems

  • Perform peptide competition assays

  • Consider monoclonal antibodies if polyclonal shows cross-reactivity

  • For the EMC4 antibody [EPR15081], specificity for human samples has been validated

• Inconsistent results between applications:

  • Note that some antibodies are validated for specific applications only

  • The EPR15080 clone has been validated for IP, WB, and IHC-P applications with human and mouse samples

  • Polyclonal antibodies from Atlas Antibodies are validated for IHC, ICC-IF, and WB applications

• Variability between tissue/cell types:

  • Consider the expression level of EMC4 in your experimental system

  • EMC4 is notably expressed in colon, cerebral cortex, cerebellum, caudate, and adrenal gland

  • Optimize protocols based on the specific sample type being analyzed

How can proximity labeling techniques be used to study EMC4 protein interactions?

Proximity labeling represents a powerful approach for identifying EMC4 interaction partners, particularly for capturing weak or transient interactions that might be missed by traditional co-immunoprecipitation techniques. The search results describe a successful application of BioID proximity labeling for EMC4 :

• BioID methodology for EMC4:

  • Generate fusion constructs like Myc-BioID2-EMC4 (with BioID2 fused to the cytosolic N-terminus of EMC4)

  • Express the construct in cells and provide biotin in the medium (typically 50 μM for 16-24 hours)

  • Lyse cells under stringent conditions and capture biotinylated proteins using streptavidin beads

  • Analyze captured proteins by Western blotting or mass spectrometry

• Validation approaches:

  • Confirm proper localization of the fusion protein (e.g., Myc-BioID2-EMC4 should localize to the ER like endogenous EMC4)

  • Include appropriate controls (e.g., Myc-BioID2 alone)

  • Validate positive hits using orthogonal methods like co-immunoprecipitation

• Advantages for EMC4 research:

  • Can identify interactions at native expression levels without overexpression artifacts

  • Captures physiologically relevant spatial relationships

  • Works well for membrane proteins like EMC4 that may have hydrophobic interaction surfaces

  • The BioID approach can identify weak or transient interactions that might be missed by other techniques

In EMC4 research, this approach successfully identified an interaction between EMC4 and Rab7, revealing EMC4's role in tethering late endosomes to the ER membrane .

What experimental approaches can determine the topology and structural characteristics of EMC4?

Understanding EMC4's membrane topology and structural features is crucial for elucidating its function. Several experimental approaches can determine these characteristics:

• Protease protection assays:

  • Prepare microsomes or semi-permeabilized cells

  • Treat with proteases (e.g., trypsin, proteinase K) with or without membrane-disrupting detergents

  • Analyze EMC4 fragments by Western blotting with domain-specific antibodies

  • Protected fragments indicate domains inside membrane-enclosed spaces

• Glycosylation mapping:

  • Introduce artificial N-glycosylation sites at different positions in EMC4

  • Express in cells and assess glycosylation status by endoglycosidase H sensitivity

  • Glycosylated sites must have accessed the ER lumen during biogenesis

• Cysteine accessibility methods:

  • Introduce cysteine residues at various positions

  • Treat intact cells or microsomes with membrane-impermeable sulfhydryl reagents

  • Modified cysteines indicate exposure to cytosol or extracellular/luminal space

• Fluorescence techniques:

  • Generate split-GFP constructs to determine which domains can complement cytosolic or luminal GFP fragments

  • Use FRET pairs to measure proximity between domains

  • Apply super-resolution microscopy to visualize EMC4 organization within the ER membrane

• Computational approaches:

  • Use hydropathy plots and transmembrane prediction algorithms

  • Apply co-evolutionary analysis to predict structural constraints

  • Molecular modeling based on related proteins with known structures

These approaches can help determine which regions of EMC4 are exposed to the cytosol, embedded in the membrane, or facing the ER lumen—information critical for understanding how EMC4 contributes to the membrane protein insertion function of the EMC complex.

How does EMC4 contribute to cell type-specific functions?

While EMC4's fundamental role in membrane protein insertion appears broadly conserved, emerging evidence suggests potential cell type-specific functions. Researchers investigating this aspect should consider:

• Tissue expression profiling:

  • EMC4 shows notable expression in colon, cerebral cortex, cerebellum, caudate, and adrenal gland

  • Compare EMC4 expression levels across cell types using transcriptomics and proteomics databases

  • Investigate whether alternative EMC4 isoforms are expressed in specific tissues (up to 3 different isoforms have been reported)

• Client protein specificity:

  • Different cell types express distinct membrane proteomes

  • Investigate whether EMC4 preferentially facilitates insertion of cell type-specific membrane proteins

  • Screen for membrane proteins whose expression depends on EMC4 in particular cell types

• EMC complex composition:

  • Analyze whether EMC4's integration into the EMC complex varies across cell types

  • Investigate whether EMC4 forms cell type-specific interactions beyond the core EMC complex

• Functional knockout studies:

  • Generate conditional EMC4 knockout models in specific tissues

  • Assess differential phenotypes across cell types upon EMC4 depletion

  • Complement with rescue experiments to confirm specificity

The cell type-specific expression pattern of EMC4 suggests it may have specialized functions beyond its general role in membrane protein insertion, possibly related to tissue-specific membrane proteomes or organelle interaction networks.

What methodological approaches can connect EMC4 function to broader cellular phenotypes?

To understand how EMC4's molecular functions translate to broader cellular phenotypes, researchers can employ these methodological approaches:

• Global proteomics and membrane proteome analysis:

  • Compare membrane protein abundance in control versus EMC4-depleted cells

  • Use stable isotope labeling (SILAC) or TMT-based quantitative proteomics

  • Focus on changes in membrane protein families known to require EMC

• Functional genomics screens:

  • Perform genetic interaction screens using CRISPR interference or overexpression libraries

  • Identify synthetic lethal or synthetic viable interactions with EMC4

  • Map EMC4 into functional networks through genetic interaction profiles

• High-content imaging approaches:

  • Develop cellular assays for organelle morphology, membrane contact sites, or protein trafficking

  • Apply automated microscopy to quantify phenotypes in EMC4-manipulated cells

  • Implement machine learning to identify subtle phenotypic signatures

• Viral infection models:

  • Utilize the established SV40 infection model where EMC4 has a documented role

  • Extend to other viral systems to determine conservation of function

  • Dissect the mechanism of EMC4-dependent viral entry through mutagenesis

• Tissue-specific and developmental studies:

  • Examine temporal regulation of EMC4 during differentiation processes

  • Investigate tissue-specific requirements for EMC4 in model organisms

  • Connect to human disease phenotypes through patient-derived samples

These approaches can help bridge the gap between EMC4's molecular functions in membrane protein insertion and late endosome-ER tethering to broader physiological or pathological phenotypes.