Recombinant Human Erlin-2 (ERLIN2)

What is the structural composition of human ERLIN2?

Human ERLIN2 is an endoplasmic reticulum membrane protein containing an evolutionarily conserved stomatin/prohibitin/flotillin/HflK/C (SPFH) domain. The full-length protein contains 339 amino acids, though recombinant versions typically express fragments such as the range from amino acids 25-339. ERLIN2 belongs to the band 7/mec-2 protein family. The N-terminus of ERLIN2 is particularly important as it contains sequences sufficient for targeting the protein to the endoplasmic reticulum, even in the absence of classical ER retrieval motifs . This N-terminal region distinguishes ERLIN2's subcellular localization from other prohibitin family members, which may target to mitochondria, plasma membrane, or Golgi vesicles.

What are the primary cellular functions of ERLIN2?

ERLIN2 serves multiple cellular functions centered around endoplasmic reticulum processes:

• ERLIN2 forms a complex with ERLIN1 (the ERLIN1/ERLIN2 complex) which mediates endoplasmic reticulum-associated degradation (ERAD) of inositol 1,4,5-trisphosphate receptors (IP3Rs) .

• It promotes sterol-accelerated ERAD of HMG-CoA reductase (HMGCR), likely involving an AMFR/gp78-containing ubiquitin ligase complex .

• ERLIN2 regulates cellular cholesterol homeostasis through the SREBP signaling pathway and may promote ER retention of the SCAP-SREBF complex .

• Recent research has identified ERLIN2 as an ER–microtubule-binding protein that interacts with α-tubulin, with this interaction peaking during the G2/M phase of the cell cycle .

• ERLIN2 plays a role in cell cycle progression by interacting with and stabilizing mitosis-promoting factors, specifically facilitating K63-linked ubiquitination and stabilization of Cyclin B1 protein during G2/M phase .

What expression systems are optimal for producing recombinant human ERLIN2?

Recombinant human ERLIN2 is commonly expressed in Escherichia coli bacterial systems, particularly for fragments like the 25-339 amino acid range . This approach typically yields protein with >95% purity suitable for applications such as SDS-PAGE. For researchers requiring post-translational modifications more similar to native human ERLIN2, mammalian expression systems may be preferable, though these are not discussed in the provided search results.

When designing expression constructs, consideration must be given to:

• Including appropriate affinity tags (e.g., His-tag) for purification

• Whether to express full-length protein or specific domains

• Solubility enhancement strategies, as membrane proteins can be challenging to express

For experimental protocols requiring study of ERLIN2's native membrane environment, insect cell or mammalian expression systems may provide advantages over bacterial systems, though specific optimization would be required.

What purification methods are most effective for recombinant ERLIN2?

For His-tagged recombinant ERLIN2, immobilized metal affinity chromatography (IMAC) is typically the primary purification method. Based on the information for commercial recombinant ERLIN2, researchers should consider:

• Protein denaturation state - denatured ERLIN2 (as in ab136707) is suitable for specific applications like antibody production and immunogen preparation .

• Purity verification - SDS-PAGE analysis should confirm the expected molecular weight and purity level (typically >95%) .

• Secondary purification steps - size exclusion or ion exchange chromatography may be required depending on experimental needs.

For studies requiring native conformation, non-denaturing purification conditions would be necessary, particularly when investigating ERLIN2's interactions with binding partners such as α-tubulin or Cyclin B1/Cdk1 .

How is ERLIN2 implicated in cancer, particularly breast cancer?

ERLIN2 has significant implications in breast cancer progression and malignancy. The gene encoding ERLIN2 is amplified in human breast cancers and plays a crucial role in cancer cell proliferation through multiple mechanisms:

• ERLIN2 is highly expressed in aggressive human breast cancers, while in normal development it is expressed at the postnatal stage and becomes undetectable in adulthood .

• Through its interaction with microtubules and the mitosis-promoting complex Cyclin B1/Cdk1, ERLIN2 facilitates cell cycle progression, particularly at the G2/M phase transition .

• ERLIN2 specifically promotes K63-linked ubiquitination and stabilization of Cyclin B1 protein, which is essential for mitotic progression .

• Experimental downregulation of ERLIN2 results in:

  • Cell cycle arrest

  • Repression of breast cancer proliferation and malignancy

  • Increased sensitivity of breast cancer cells to anticancer drugs

These findings suggest ERLIN2 could be a potential therapeutic target in breast cancer treatment strategies, particularly for aggressive forms with high ERLIN2 expression.

What is known about ERLIN2 mutations in neurodegenerative disorders?

ERLIN2 mutations are associated with a spectrum of motor neuron diseases with varying inheritance patterns and severity:

• SPG18 (Spastic Paraplegia 18): Caused by homozygous nullimorphic deletion/frameshift mutations or compound heterozygous splice site/missense mutations in ERLIN2. This is a recessive hereditary spastic paraplegia characterized by degeneration of upper motor neurons leading to weakness and spasticity restricted to the lower limbs .

• Juvenile primary lateral sclerosis: Associated with ERLIN2 mutations affecting upper motor neurons with onset in early childhood .

• Intellectual disability, motor dysfunction, and joint contractures (IDMDC): A neurologic disorder linked to ERLIN2 mutations .

• Amyotrophic Lateral Sclerosis (ALS): Recent research has identified ERLIN2 mutations in patients with primarily spastic paraplegia evolving to rapid progressive ALS. These mutations can segregate with disease in either dominant (V168M) or recessive (D300V) inheritance patterns, or appear in sporadic cases (N125S) .

The inheritance patterns for ERLIN2-related neurodegenerative disorders are complex:

• Recessive inheritance: Classical SPG18 cases

• Dominant inheritance: Recently reported in both pure hereditary spastic paraplegia and in cases progressing to ALS

This phenotypic spectrum and variable inheritance patterns complicate genetic counseling for affected families. Some mutations (e.g., D300V) have been identified in both pure spastic paraplegia and in cases progressing to ALS, suggesting additional genetic modifiers may influence disease progression .

What is the proposed mechanism for ERLIN2-associated motor neuron pathology?

The pathogenic mechanism of ERLIN2 mutations in motor neuron diseases appears to involve disruption of cellular calcium signaling and protein degradation pathways:

• ERLIN2 normally participates in the endoplasmic reticulum–associated degradation pathway of inositol 1,4,5-trisphosphate receptors (IP3Rs) through ubiquitination .

• The homozygous null alleles identified in SPG18 patients suggest that loss of ERLIN2 function leads to persistent activation of IP3R and neuronal channels .

• This disruption likely affects calcium homeostasis within neurons, which is critical for motor neuron survival and function.

• The progression from spastic paraplegia to ALS observed in some patients suggests that deterioration of these cellular mechanisms can eventually affect both upper and lower motor neurons .

• The mean disease duration before conversion from spastic paraplegia to ALS phenotype ranges from 20 to 45 years and appears to be increased when spastic paraplegia disease onset occurs earlier .

The variable expressivity observed even within families carrying the same mutation suggests additional genetic modifiers may influence disease severity and progression. Whether the mechanisms causing pure spastic paraplegia are identical to those causing progression to ALS remains to be fully investigated .

What techniques are most effective for studying ERLIN2's interaction with microtubules and cell cycle proteins?

To investigate ERLIN2's interactions with microtubules and cell cycle proteins such as Cyclin B1/Cdk1, researchers should consider multiple complementary approaches:

• Co-immunoprecipitation (Co-IP): Useful for confirming physical interactions between ERLIN2 and α-tubulin or Cyclin B1/Cdk1. This approach can be combined with cell synchronization techniques to examine cell cycle phase-specific interactions .

• Proximity ligation assays: These provide spatial resolution of protein interactions within cells, helping to confirm that ERLIN2-protein interactions occur in the expected subcellular compartments.

• Immunofluorescence microscopy: Essential for visualizing co-localization of ERLIN2 with microtubules throughout the cell cycle. Particularly valuable during mitosis when dramatic reorganization of the microtubule network occurs .

• Live-cell imaging with fluorescently tagged proteins: Allows real-time visualization of ERLIN2's dynamic interactions during cell cycle progression.

• Cell cycle synchronization: Methods such as thymidine block or nocodazole treatment can enrich cells at specific cell cycle phases to study the temporal regulation of ERLIN2 interactions .

• Ubiquitination assays: Essential for investigating ERLIN2's role in facilitating K63-linked ubiquitination of Cyclin B1. These typically involve immunoprecipitation of Cyclin B1 followed by Western blotting with ubiquitin-specific antibodies .

• RNA interference or CRISPR-based gene editing: These approaches allow for functional assessment of how ERLIN2 depletion affects cell cycle progression and partner protein stability .

What methodological approaches best reveal ERLIN2's role in ER lipid raft domains?

ERLIN2 was initially identified as a component of lipid raft-like domains in the ER, and investigating this aspect requires specialized techniques:

• Detergent resistance assays: ERLIN2 is highly enriched in detergent-insoluble, buoyant fractions of sucrose gradients in a cholesterol-dependent manner . This technique involves:

  • Cell lysis in cold detergent (typically Triton X-100)

  • Sucrose gradient ultracentrifugation

  • Analysis of protein distribution across gradient fractions

• Cholesterol depletion experiments: Treating cells with cholesterol-depleting agents (e.g., methyl-β-cyclodextrin) can reveal cholesterol-dependent localization patterns of ERLIN2 .

• Membrane fractionation: Differential centrifugation to isolate ER membranes, followed by further separation of ER subdomains.

• Protein domain mapping: The N-terminus of ERLIN2 is sufficient for heterologous targeting of GFP to the ER. Engineering truncation or chimeric constructs can reveal which domains are necessary and sufficient for lipid raft association .

• Super-resolution microscopy: Techniques like STORM, PALM, or structured illumination microscopy provide nanoscale resolution of ERLIN2 distribution within ER membranes, potentially revealing organization within lipid raft microdomains.

• Quantitative proteomics of isolated ER lipid rafts: Mass spectrometry-based approaches to catalog the protein composition of ERLIN2-containing membrane domains.

What are the current contradictions in understanding ERLIN2's role in IP3R regulation?

While ERLIN2 is known to participate in IP3R degradation, several aspects of this function remain incompletely understood:

Researchers addressing these questions would benefit from combining cellular and biochemical approaches with patient-derived cellular models (e.g., iPSC-derived motor neurons carrying ERLIN2 mutations) to establish causal relationships between molecular mechanisms and disease phenotypes.

How might therapeutic strategies targeting ERLIN2 be developed for breast cancer?

Based on ERLIN2's role in breast cancer progression, several potential therapeutic approaches warrant investigation:

• Direct inhibition strategies:

  • Small molecule inhibitors that disrupt ERLIN2's interaction with Cyclin B1/Cdk1

  • Compounds that interfere with ERLIN2's microtubule-binding capacity

  • Peptide-based inhibitors mimicking critical binding interfaces

• Degradation-based approaches:

  • Proteolysis-targeting chimeras (PROTACs) directed against ERLIN2

  • Leveraging ERLIN2's own ubiquitination pathways (it is deubiquitinated by USP25, leading to stabilization)

• Combination therapy approaches:

  • Combining ERLIN2 inhibition with standard chemotherapies, as ERLIN2 downregulation increases sensitivity of breast cancer cells to anticancer drugs

  • Identifying synthetic lethal interactions with ERLIN2 expression

• Addressing therapeutic resistance:

  • Investigating mechanisms of resistance to ERLIN2-targeted therapies

  • Identifying biomarkers predictive of response to ERLIN2 inhibition

Developing effective ERLIN2-targeted therapies would require robust target validation, medicinal chemistry efforts, and careful preclinical evaluation in appropriate breast cancer models.

What are common challenges when working with recombinant ERLIN2 protein?

Researchers working with recombinant ERLIN2 may encounter several technical challenges:

• Protein solubility issues: As an ER membrane protein, native ERLIN2 contains hydrophobic regions that may cause aggregation or precipitation. Researchers may need to:

  • Use detergents or lipid environments to maintain solubility

  • Work with specific soluble domains rather than full-length protein

  • Consider fusion partners to enhance solubility

• Maintaining native conformation: Ensuring that recombinant ERLIN2 retains its physiologically relevant conformation is challenging. Approaches include:

  • Careful selection of purification conditions

  • Validation of protein folding using circular dichroism spectroscopy

  • Functional assays to confirm activity

• Replicating post-translational modifications: E. coli-expressed ERLIN2 will lack mammalian post-translational modifications. If these are important for your research, consider:

  • Mammalian expression systems

  • Insect cell expression

  • In vitro modification approaches where applicable

• Protein-protein interaction studies: When investigating ERLIN2's interactions with partners like α-tubulin or Cyclin B1/Cdk1, researchers should:

  • Validate interactions using multiple complementary techniques

  • Consider the temporal nature of these interactions (particularly cell cycle-dependent interactions)

  • Include appropriate controls to rule out non-specific binding

What methodological considerations are important when studying ERLIN2 mutations in neurodegenerative disorders?

When investigating ERLIN2 mutations in the context of neurodegenerative disorders, researchers should consider:

• Model system selection:

  • Patient-derived samples (where available)

  • iPSC-derived motor neurons carrying ERLIN2 mutations

  • Animal models with equivalent mutations

  • Simple cellular models for initial mechanistic studies

• Genotype-phenotype correlation analyses:

  • Consider the inheritance pattern (dominant vs. recessive)

  • Account for variable expressivity within families

  • Track disease progression from spastic paraplegia to ALS when applicable

• Functional studies:

  • Examine IP3R degradation efficiency

  • Measure calcium signaling dynamics

  • Assess ER stress responses

  • Evaluate motor neuron-specific vulnerability

• Biomarker development:

  • Identify markers predictive of disease progression

  • Develop tools to monitor conversion from spastic paraplegia to ALS phenotype

• Genetic background considerations:

  • Search for genetic modifiers that influence disease severity

  • Consider whole genome/exome sequencing of affected families to identify potential modifier genes

These methodological considerations are essential for effectively translating genetic findings into mechanistic understanding and potential therapeutic approaches.