Recombinant Mouse Transmembrane protein C9orf91 homolog

How does mouse C9orf91 homolog compare to its human counterpart?

The human C9orf91 homolog (TMEM268) and mouse variant share considerable sequence homology, though with notable differences. The table below compares key characteristics of both proteins:

Sequence alignment reveals high conservation of transmembrane domains and functional motifs between species, suggesting evolutionary pressure to maintain structural integrity of this protein for its biological function.

What are the recommended storage conditions for recombinant mouse C9orf91 homolog?

For optimal stability and activity of recombinant mouse C9orf91 homolog, storage conditions must be carefully controlled. Store the protein at -20°C for regular use, or at -80°C for extended storage periods . Working aliquots should be maintained at 4°C for no longer than one week to preserve activity . Repeated freeze-thaw cycles should be strictly avoided as they significantly degrade protein structure and function .

For the human version, similar principles apply, with storage recommended at -80°C . Under proper storage and handling conditions, the protein remains stable for approximately 12 months from the date of receipt .

What experimental approaches are suitable for studying the subcellular localization of C9orf91?

To investigate the subcellular localization of C9orf91, researchers can employ multiple complementary techniques:

Fluorescent Fusion Protein Expression: Following molecular cloning approaches similar to those used for other transmembrane proteins, C9orf91 can be expressed as a GFP or YFP fusion protein . This technique allows for real-time visualization of protein trafficking and localization in living cells. The cloning procedure involves:

• Obtaining the IMAGE or ORFEOME clone coding for the protein

• Amplifying the insert by PCR using high-fidelity polymerase such as Phusion

• Cloning the amplified insert into appropriate expression vectors for fluorescent tagging

Subcellular Fractionation: For biochemical confirmation of localization, subcellular fractionation can be performed following protocols established for lysosomal and membrane proteins:

• Homogenization of tissue or cells

• Differential centrifugation to separate cellular components

• Density gradient centrifugation (e.g., using Nycodenz) for further purification

• Confirmation of fraction purity using marker enzyme assays (e.g., β-galactosidase)

How can researchers optimize expression and purification of recombinant C9orf91 for functional studies?

Optimization of recombinant C9orf91 expression and purification requires careful consideration of multiple parameters:

Expression Systems: While HEK293T cells are commonly used for human C9orf91 expression , comparing yields and functionality across different expression systems (bacterial, insect, mammalian) is advisable for mouse C9orf91. Mammalian systems often provide better folding and post-translational modifications for transmembrane proteins.

Purification Strategy:

• For transmembrane proteins like C9orf91, solubilization requires careful selection of detergents:

  • Initial membrane isolation through ultracentrifugation (100,000 × g, 40 min, 4°C)

  • Resuspension in buffer followed by solubilization in chloroform-methanol (CM, 5:4, v/v)

  • Separation of CM-soluble fraction containing hydrophobic proteins

  • Precipitation and further purification through affinity chromatography

• For tagged versions, affinity purification can be performed:

  • Capture through anti-tag (e.g., DDK) affinity column

  • Further purification through conventional chromatography steps

  • Quality assessment using SDS-PAGE and Coomassie blue staining, aiming for >80% purity

What are the current hypotheses regarding the function of C9orf91/TMEM268 in cellular physiology?

While specific functions of C9orf91/TMEM268 remain under investigation, several hypotheses can be formulated based on its structural features and conservation:

• Membrane Transport: The transmembrane nature of C9orf91 suggests potential involvement in transport processes across cellular membranes, potentially as part of the broader transmembrane protein family .

• Evolutionary Conservation: The presence of C9orf91 in organisms from fruit flies to mammals, but absence in simpler organisms, suggests acquisition of function during evolution of more complex multicellular organisms .

• Alternative Splicing Regulation: The existence of eight alternative splice variants in humans suggests complex regulation and potentially diverse functional roles depending on tissue or developmental context.

Further investigation using knockout/knockdown studies, protein-protein interaction analyses, and transcriptomic profiling would be necessary to elucidate the precise functions.

What strategies can be employed for CRISPR-mediated genome editing of C9orf91 in mouse models?

CRISPR-mediated genome editing of C9orf91 requires careful design and optimization:

Homology Arm Design: The length of homology arms plays an essential role in increasing HDR (Homology Directed Repair) rates . For optimal editing efficiency:

• Design homology arms of sufficient length (typically 500-1000 bp for each arm)

• Ensure the homology arms directly flank the intended edit site

• Verify specificity of homology arms through sequence analysis to prevent off-target integration

gRNA Design Considerations:

• Select gRNA target sites with high on-target efficiency and minimal off-target potential

• For knock-in mutations, position the cut site as close as possible to the intended mutation site

• Validate gRNA efficiency through in vitro assays before proceeding to cell or animal models

HDR Template Design:

• For point mutations (e.g., creating specific amino acid changes), single-stranded oligodeoxynucleotide (ssODN) donors are often sufficient

• For larger modifications, double-stranded DNA donors with longer homology arms are typically required

• Include silent mutations in the PAM site or gRNA binding region to prevent re-cutting of edited alleles

What quality control measures should be implemented when working with recombinant C9orf91?

To ensure reproducible results, implement the following quality control measures:

Protein Purity Assessment:

• SDS-PAGE analysis with Coomassie blue staining (aim for >80% purity)

• Western blot confirmation of identity using specific antibodies

• Mass spectrometry validation of full sequence and post-translational modifications

Functional Verification:

• Circular dichroism to assess secondary structure integrity

• Size exclusion chromatography to confirm monodispersity and absence of aggregation

• Activity assays relevant to hypothesized function

Storage Stability Monitoring:

• Regular assessment of aliquots stored under different conditions

• Implementation of strict freeze-thaw protocols to prevent degradation

• Documentation of batch-to-batch variability

How can researchers develop specific antibodies against mouse C9orf91 for immunodetection?

Development of specific antibodies against mouse C9orf91 requires strategic epitope selection and validation:

Epitope Selection Strategy:

• Analyze the protein sequence for regions of high antigenicity and surface accessibility

• Compare mouse and human sequences to identify species-specific epitopes for creating mouse-specific antibodies

• Avoid highly conserved functional domains if the goal is specificity rather than cross-reactivity

Antibody Production Workflow:

• Synthesize peptide antigens or express protein fragments for immunization

• Employ polyclonal approaches for initial detection and monoclonal development for specificity

• Validate antibodies through:

  • Western blotting against recombinant protein

  • Immunoprecipitation followed by mass spectrometry

  • Immunohistochemistry with appropriate positive and negative controls

  • Testing in C9orf91 knockout models as ultimate specificity control

What are common challenges in expressing and purifying transmembrane proteins like C9orf91, and how can they be addressed?

Transmembrane proteins present several challenges during expression and purification:

Low Expression Yields:

• Optimize codon usage for the expression system

• Test different promoters and expression vectors

• Evaluate various fusion tags beyond standard C-Myc/DDK to enhance solubility and expression

• Consider inducible expression systems to mitigate potential toxicity

Protein Misfolding:

• Express in mammalian cells (e.g., HEK293T) rather than prokaryotic systems

• Optimize growth temperature and induction conditions

• Co-express with molecular chaperones

• Include stabilizing agents in growth media

Solubilization Difficulties:

• Screen multiple detergents before settling on a final purification protocol

• Consider native nanodiscs or other membrane-mimetic systems

• Employ the chloroform-methanol extraction method as described for hydrophobic membrane proteins

• Optimize detergent:protein ratios carefully

How can researchers distinguish between the functions of endogenous C9orf91 and recombinant tagged versions?

When investigating protein function, distinguishing between endogenous and recombinant tagged versions is critical:

Experimental Strategies:

• Generate knockout/knockdown cell lines as clean backgrounds for expressing tagged variants

• Use RNA interference to specifically target endogenous transcripts while expressing RNAi-resistant recombinant versions

• Design antibodies that specifically recognize either the native protein or the tagged version

Rescue Experiments:

• Document phenotypes in knockout/knockdown models

• Perform complementation studies with untagged and differently tagged versions

• Create a series of domain deletion or point mutation variants to identify functional regions

Controls for Tag Interference:

• Compare multiple tag positions (N-terminal, C-terminal, internal)

• Include tag-only controls in all experiments

• Validate function through complementary techniques that don't rely on the tag

What analytical techniques are most suitable for studying protein-protein interactions involving C9orf91?

Several complementary approaches can be employed to investigate C9orf91 interaction partners:

Proximity-based Methods:

• BioID or TurboID proximity labeling in living cells

• APEX2-based proximity labeling for spatially and temporally controlled mapping

• Split-protein complementation assays for direct binary interactions

Affinity-based Methods:

• Co-immunoprecipitation using anti-tag antibodies for recombinant C9orf91

• Crosslinking mass spectrometry (XL-MS) to capture transient interactions

• Label-free quantitative proteomics comparing bait vs. control pulldowns

Biophysical Techniques:

• Surface plasmon resonance for kinetic and affinity measurements

• Isothermal titration calorimetry for thermodynamic parameters

• Microscale thermophoresis for in-solution interaction analysis