Recombinant Pongo abelii Transmembrane protein C9orf71 homolog

What is the Pongo abelii Transmembrane protein C9orf71 homolog and how is it characterized?

The Transmembrane protein C9orf71 homolog is a protein found in Pongo abelii (Sumatran orangutan) with UniProt identification number Q5RF75. It is a full-length protein consisting of 170 amino acids with the sequence: MQNRTGLILCALALLMGFLMVCLGAFFISWGSIFDCQGSLIAAYLLLPLGFVILLSGIFWSNYRQVTESKGVLRHMLRQHLAHGALSVATVDRPDFYPPAYEESLEVEKQSCPAEREASGI PPPLYTETGLEFQDGNDSHPEAPPSYRESIASLVVTAISEDAQRRGQEC . As indicated by its name, it spans cellular membranes and likely serves functions related to membrane biology.

The protein is typically studied as a recombinant protein expressed in heterologous systems, which allows for analysis of its biochemical properties and functional characteristics. Characterization methods include structural analysis, localization studies, and functional assays to determine its role in cellular processes.

What are the optimal storage and handling conditions for recombinant C9orf71 homolog protein?

For optimal preservation of the recombinant C9orf71 homolog, the protein should be stored at -20°C for routine storage, or at -80°C for extended preservation . The protein is typically supplied in a Tris-based buffer containing 50% glycerol optimized for protein stability. To maintain protein integrity, it's crucial to avoid repeated freeze-thaw cycles that can lead to denaturation and loss of activity.

For active research, working aliquots can be stored at 4°C for up to one week . When planning experiments, it's advisable to create small single-use aliquots during initial thawing to minimize degradation from multiple freeze-thaw cycles. Always handle the protein on ice when preparing experimental samples, and consider adding protease inhibitors if working with cell or tissue extracts to prevent degradation.

How is the C9orf71 homolog related to human C9orf72 and what are the evolutionary implications?

The Pongo abelii C9orf71 homolog likely shares functional similarities with the human C9orf72 protein, which has been implicated in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) . Structurally, both proteins contain DENN (Differentially Expressed in Normal and Neoplastic cells) domains, suggesting evolutionary conservation of function related to membrane trafficking and GTPase regulation across primate species.

From an evolutionary perspective, studying the orangutan C9orf71 homolog provides insights into the conservation of cellular pathways involved in neurodegeneration. The human C9orf72 gene harbors a hexanucleotide repeat expansion that causes disease through potential haploinsufficiency mechanisms, similar to progranulin haploinsufficiency in FTD . Comparative analysis between the orangutan homolog and human protein can reveal evolutionary adaptations in membrane trafficking systems and potentially identify conserved domains that are critical for function, which might represent therapeutic targets for neurodegenerative diseases.

What are the key methodological approaches for studying C9orf71 homolog subcellular localization?

When investigating the subcellular localization of C9orf71 homolog, researchers should consider multiple complementary methodologies to ensure robust findings:

• Immunofluorescence microscopy:

  • Use specific antibodies against the native protein or epitope tags

  • Co-stain with established markers for cellular compartments (plasma membrane, endosomes, lysosomes, Golgi)

  • Apply super-resolution techniques (STED, STORM, PALM) for detailed localization

• Live-cell imaging with fluorescent protein fusions:

  • Consider both N- and C-terminal tags to determine which preserves native localization

  • Use photoactivatable or photoswitchable fluorescent proteins for tracking dynamics

  • Implement FRAP (Fluorescence Recovery After Photobleaching) to assess mobility

• Biochemical fractionation:

  • Perform differential centrifugation to separate cellular compartments

  • Use density gradient fractionation for finer resolution

  • Validate fractionation quality with compartment-specific markers

• Topology mapping:

  • Employ protease protection assays to determine membrane orientation

  • Use glycosylation mapping to identify luminal domains

  • Apply site-directed labeling techniques for accessible regions

These approaches should be implemented with appropriate controls, including cells not expressing the protein and comparative analysis with related proteins of known localization. Given the transmembrane nature of C9orf71 homolog, special attention should be paid to membrane extraction and fixation protocols to preserve native localization patterns.

How should researchers design experiments to investigate potential GTPase regulatory functions of C9orf71 homolog?

Investigating the potential GTPase regulatory functions of C9orf71 homolog requires a systematic experimental design approach:

• Identification of candidate GTPase partners:

  • Pull-down assays with immobilized C9orf71 homolog protein

  • Proximity labeling (BioID, APEX) in cellular contexts

  • Co-immunoprecipitation studies followed by mass spectrometry

  • Based on structural similarities to FLCN-FNIP, focus on Rag GTPases

• GEF activity assessment:

  • Fluorescence-based nucleotide exchange assays using mant-GDP/GTP

  • Monitor GDP release and GTP binding rates in the presence of C9orf71

  • Compare exchange rates with known GEFs and negative controls

  • Test nucleotide specificity (GDP vs. GTP preference)

• GAP activity evaluation:

  • Single-turnover GTPase assays measuring stimulation of GTP hydrolysis

  • Phosphate release assays using colorimetric detection

  • Include positive controls (known GAPs) and negative controls

• Structural basis of interactions:

  • Generate domain deletion constructs to map interaction regions

  • Perform site-directed mutagenesis of conserved residues

  • Use biophysical methods (ITC, SPR) to quantify binding affinities

• Cellular validation:

  • Assess GTPase activation states using conformation-specific antibodies

  • Implement FRET-based biosensors to monitor GTPase activity in cells

  • Evaluate downstream signaling pathway activation

A comprehensive experimental design should include appropriate controls, concentration-dependent measurements, and validation across multiple experimental systems to establish physiologically relevant GTPase regulatory functions.

What strategies can address common challenges in expressing and purifying functional recombinant C9orf71 homolog?

Membrane proteins like C9orf71 homolog present significant challenges for recombinant expression and purification. The following strategies can help overcome these difficulties:

• Expression system optimization:

  • Compare prokaryotic (E. coli C41/C43 strains) and eukaryotic systems (insect cells, mammalian cells)

  • Evaluate cell-free expression systems with membrane mimetics

  • Test codon-optimized constructs for the expression host

  • Implement inducible expression systems with titratable promoters

• Fusion partner selection:

  • Incorporate solubility-enhancing tags (MBP, SUMO, Trx)

  • Consider fluorescent protein fusions as folding indicators

  • Use affinity tags (His, FLAG, Strep) for purification

  • Include cleavable linkers for tag removal

• Membrane protein solubilization:

  • Screen multiple detergents (DDM, LMNG, digitonin) at various concentrations

  • Evaluate native nanodiscs or SMALPs for detergent-free extraction

  • Test amphipols for stabilizing the protein after extraction

  • Consider bicelles or lipid cubic phase for structure-function studies

• Expression condition optimization:

  • Reduce temperature during expression (16-20°C)

  • Implement slow induction protocols with low inducer concentrations

  • Co-express with chaperones to improve folding

  • Use chemical chaperones (glycerol, DMSO at low concentrations)

• Purification workflow refinement:

  • Implement two-step or multi-step purification strategies

  • Include size exclusion chromatography as a final step

  • Validate protein integrity using activity assays after each step

  • Consider on-column refolding approaches for aggregation-prone constructs

These strategies should be systematically evaluated and combined as needed to obtain properly folded, functional recombinant C9orf71 homolog protein suitable for downstream applications.

What specialized techniques should be employed to study potential roles of C9orf71 homolog in lysosomal biology and nutrient sensing?

Based on structural similarities with FLCN and FNIP proteins, the C9orf71 homolog may function in lysosomal biology and nutrient sensing pathways . To investigate these aspects, researchers should employ these specialized techniques:

• Nutrient-dependent localization studies:

  • Track protein localization under various nutrient conditions (amino acid starvation/refeeding)

  • Co-localize with mTORC1 components and Rag GTPases at lysosomes

  • Implement live-cell imaging with nutrient perfusion systems

• Lysosome function assessment:

  • Measure lysosomal pH using ratiometric probes in cells with modulated C9orf71 expression

  • Evaluate lysosomal enzyme activity and processing

  • Assess autophagy flux using LC3 conversion and p62 degradation assays

  • Monitor lysosomal positioning and distribution

• Nutrient sensing pathway analysis:

  • Quantify mTORC1 activation (S6K, 4E-BP1 phosphorylation) in response to amino acids

  • Examine TFEB/TFE3 localization and activation as downstream readouts

  • Monitor amino acid-dependent Rag GTPase nucleotide loading states

  • Assess interactions with known nutrient sensing components (Ragulator, v-ATPase)

• Reconstitution systems:

  • Develop purified component systems to reconstitute sensing mechanisms

  • Use artificial liposomes with reconstituted proteins to study membrane interactions

  • Implement optogenetic tools for acute recruitment to lysosomes

• Metabolic profiling:

  • Perform metabolomics analysis under C9orf71 depletion/overexpression

  • Track amino acid uptake and utilization

  • Examine energetic adaptations to nutrient stress

These methodologies, implemented with appropriate controls and quantitative readouts, can reveal C9orf71 homolog's potential functions in nutrient-responsive cellular pathways and lysosomal biology.

How can comparative genomics approaches reveal insights about C9orf71 homolog evolution and function?

Comparative genomics offers powerful approaches to understand C9orf71 homolog evolution and function across species:

• Phylogenetic analysis:

  • Construct comprehensive phylogenetic trees of C9orf71 homologs across primates and other mammals

  • Compare evolutionary rates with other DENN domain proteins

  • Identify critical divergence points that may correlate with functional adaptations

• Positive selection analysis:

  • Calculate dN/dS ratios across the protein sequence

  • Identify residues under positive selection using methods like PAML

  • Map selected residues onto structural models to predict functional significance

  • Compare selection patterns between primates to identify lineage-specific adaptations

• Synteny mapping:

  • Analyze conservation of genomic neighborhood across species

  • Identify co-evolved gene clusters that might suggest functional relationships

  • Detect genomic rearrangements that may influence expression regulation

• Domain architecture analysis:

  • Compare domain organization across species using domain prediction tools

  • Identify lineage-specific domain gains/losses

  • Analyze conservation of specific motifs within domains

• Co-evolution network analysis:

  • Identify co-evolving positions within the protein using mutual information approaches

  • Detect correlated evolution with interacting partners

  • Build protein-protein interaction networks across species

• Expression pattern comparison:

  • Compare tissue-specific expression patterns across primates

  • Correlate expression changes with phenotypic adaptations

  • Identify conserved regulatory elements in promoter regions

These comparative genomics approaches can provide critical insights into the evolutionary history of C9orf71 homolog, identify functionally important regions, and suggest experimental hypotheses about its cellular roles and potential disease relevance.

What approaches are most effective for integrating structural and functional data to understand C9orf71 homolog mechanisms?

Effectively integrating structural and functional data requires a multifaceted approach that bridges different experimental scales:

• Structure-guided mutagenesis:

  • Generate homology models based on related DENN-domain proteins

  • Identify conserved surface patches for targeted mutagenesis

  • Create domain swap chimeras with related proteins

  • Test functional outcomes of mutations in cellular assays

• Structure-function correlation through integrative methods:

  • Hydrogen-deuterium exchange mass spectrometry to identify dynamic regions

  • Limited proteolysis to map domain boundaries and flexible regions

  • Cross-linking mass spectrometry to capture interaction interfaces

  • Cryo-electron microscopy of protein complexes in different functional states

• Computational integration:

  • Molecular dynamics simulations to predict conformational changes

  • Integrate AlphaFold2 predictions with experimental constraints

  • Use machine learning approaches to predict functional sites

  • Implement network analysis to connect structural features to functional datasets

• Integrated cellular imaging approaches:

  • Structure-guided fluorescent probe design for tracking conformational changes

  • FRET sensors based on structural predictions

  • High-content imaging to correlate structure-guided mutations with cellular phenotypes

  • Correlative light and electron microscopy to bridge protein localization with ultrastructure

• Systems-level integration:

  • Map mutations/domains to protein interaction networks

  • Correlate structural features with transcriptomic/proteomic responses

  • Integrate structural information with evolutionary conservation data

This integrative approach enables researchers to develop mechanistic models connecting C9orf71 homolog structure to its cellular functions, providing deeper insights than either structural or functional studies alone could achieve.

How should researchers analyze and interpret conflicting data regarding C9orf71 homolog function?

When faced with conflicting data regarding C9orf71 homolog function, researchers should implement a systematic analytical framework:

• Methodological assessment:

  • Catalog differences in experimental systems (cell types, expression levels, tags)

  • Compare assay conditions (buffer composition, temperature, pH, ionic strength)

  • Evaluate temporal aspects (acute vs. chronic manipulations, time points analyzed)

  • Consider detection method sensitivity and specificity

• Contextual dependencies evaluation:

  • Analyze cell type-specific effects (neuronal vs. non-neuronal, species differences)

  • Assess nutrient status influences (given potential roles in nutrient sensing)

  • Consider developmental or cell cycle stage variations

  • Examine potential compensatory mechanisms in different systems

• Multiple hypothesis reconciliation:

  • Consider that C9orf71 homolog may have multiple distinct functions

  • Develop integrated models that accommodate seemingly contradictory data

  • Test combinatorial hypotheses that incorporate multiple functions

  • Implement Bayesian approaches to weigh evidence for competing models

• Validation through orthogonal methods:

  • Confirm key findings using multiple independent techniques

  • Implement CRISPR-based approaches alongside RNAi or overexpression

  • Combine biochemical assays with cellular and in vivo studies

  • Use genetic rescue experiments to confirm specificity

• Quantitative analysis:

  • Develop quantitative assays with appropriate controls and statistical power

  • Perform dose-response studies to identify threshold effects

  • Implement mathematical modeling to predict system behaviors

  • Conduct meta-analysis across studies when sufficient data exists

This systematic approach allows researchers to reconcile apparent contradictions, identify context-dependent functions, and develop more nuanced models of C9orf71 homolog biology.

What are the critical considerations for analyzing C9orf71 homolog interactions with potential binding partners?

When analyzing C9orf71 homolog interactions with potential binding partners, researchers should consider these critical factors:

• Interaction specificity validation:

  • Implement reciprocal co-immunoprecipitation studies

  • Compare wild-type protein with binding-deficient mutants

  • Include appropriate negative controls (unrelated proteins of similar characteristics)

  • Test competition with predicted binding domains/peptides

• Quantitative interaction characterization:

  • Determine binding affinities using methods like SPR, BLI, or ITC

  • Measure binding kinetics (association/dissociation rates)

  • Assess stoichiometry through analytical ultracentrifugation or SEC-MALS

  • Evaluate binding under varying conditions (nucleotides, ions, pH)

• Structural basis of interactions:

  • Map minimal binding domains through truncation analysis

  • Identify critical residues through alanine scanning mutagenesis

  • Use cross-linking mass spectrometry to identify interaction interfaces

  • Develop structural models of complexes integrating experimental constraints

• Physiological relevance assessment:

  • Confirm interactions at endogenous expression levels

  • Verify co-localization in relevant subcellular compartments

  • Demonstrate functional consequences of disrupting interactions

  • Test interaction dynamics under various cellular conditions (stress, nutrient availability)

• Network context integration:

  • Place direct interactions within broader protein interaction networks

  • Identify competitive or cooperative binding with other partners

  • Determine if interactions are constitutive or regulated

  • Map interactions to relevant signaling pathways

By systematically addressing these considerations, researchers can establish not only the existence but also the functional significance of C9orf71 homolog interactions with binding partners, providing insights into its cellular mechanisms.

How can insights from C9orf71 homolog studies contribute to understanding neurodegenerative disease mechanisms?

Research on the C9orf71 homolog has significant translational implications for understanding neurodegenerative disease mechanisms, particularly for conditions linked to C9orf72 mutations in humans:

• Haploinsufficiency mechanisms:

  • C9orf71 homolog studies can help understand how ~50% reduction in protein levels leads to cellular dysfunction

  • Parallels can be drawn with progranulin haploinsufficiency in frontotemporal dementia

  • Identification of dosage-sensitive pathways can reveal therapeutic targets

• Lysosomal and autophagy dysfunction:

  • Based on structural similarities to DENN domain proteins involved in membrane trafficking

  • C9orf71 studies can illuminate conserved roles in autophagy and lysosomal function

  • These pathways are implicated in multiple neurodegenerative diseases

• Nutrient sensing and neuronal metabolism:

  • Investigating roles in nutrient response can reveal how metabolic dysregulation contributes to neurodegeneration

  • Connections to mTORC1 signaling may explain selective neuronal vulnerability

  • Energy homeostasis disruptions are common features in neurodegeneration

• Comparative models for therapeutic development:

  • C9orf71 homolog studies provide alternative models for testing therapeutic strategies

  • Conservation analysis can identify critical functional domains as drug targets

  • Cross-species validation strengthens translational potential of findings

• Biomarker development:

  • Identification of C9orf71-regulated pathways can suggest novel biomarkers

  • Molecular signatures of dysfunction may be detectable before symptom onset

  • Pathway analysis can reveal monitoring mechanisms for therapeutic efficacy

By studying the fundamental biology of the C9orf71 homolog in a comparative framework, researchers can gain insights into conserved mechanisms that may be disrupted in human C9orf72-related diseases, potentially leading to new therapeutic approaches for ALS and FTD .

What methodological approaches can connect basic C9orf71 homolog research to therapeutic development?

Bridging basic C9orf71 homolog research to therapeutic development requires methodological approaches that span from molecular characterization to translational applications:

• Target validation strategies:

  • CRISPR-based screens to identify synthetic lethal interactions with C9orf71 deficiency

  • Genetic interaction mapping to determine compensatory pathways

  • Conditional knockout models to assess temporal requirements in disease progression

  • Cross-species validation of targets in multiple model systems

• Phenotypic screening platforms:

  • Develop cellular assays based on C9orf71 function for high-throughput screening

  • Implement image-based multiplex readouts of downstream pathway activity

  • Create reporter systems for monitoring C9orf71-dependent processes

  • Validate hits using orthogonal assays and dose-response studies

• Structure-based drug design:

  • Utilize structural information for virtual screening campaigns

  • Design peptidomimetics targeting critical protein-protein interactions

  • Develop allosteric modulators of protein function

  • Implement fragment-based approaches to identify chemical starting points

• Disease-relevant model systems:

  • Generate patient-derived iPSCs with C9orf72 mutations

  • Develop organoid models that recapitulate disease features

  • Create transgenic animal models with selective manipulation of conserved pathways

  • Implement aging-related factors in model systems

• Biomarker development pipeline:

  • Identify pathway-specific biomarkers that respond to target engagement

  • Develop non-invasive monitoring methods for target activity

  • Create companion diagnostics for patient stratification

  • Implement longitudinal biomarker studies to track disease progression

These methodological approaches create a translational pipeline that connects fundamental insights from C9orf71 homolog research to therapeutic opportunities, potentially accelerating drug development for related neurodegenerative diseases.

Table 1: Comparative Properties of C9orf71 Homolog and Related Proteins

Table 2: Recommended Experimental Approaches for C9orf71 Homolog Characterization