Recombinant Rat Transmembrane protein 218 (Tmem218)
Description
Introduction to Transmembrane Protein 218
Transmembrane protein 218 (Tmem218) belongs to a class of proteins that span cellular membranes and mediate various biological functions. In rats, Tmem218 is a small protein consisting of 115 amino acids that contains a signal peptide and two transmembrane segments. This protein has gained significant research interest due to its localization in the ciliary transition zone, a specialized compartment at the base of cilia that regulates protein trafficking into and out of these important cellular organelles .
The rat Tmem218 protein shares considerable sequence homology with its counterparts in other species, including humans (81% sequence identity) and mice (85% sequence identity), suggesting evolutionary conservation and functional importance across mammalian species . This conservation underscores the fundamental biological significance of Tmem218 across different organisms and indicates its potential relevance to human health and disease.
Cilia are hair-like structures that extend from the cell surface and function in cellular signaling, sensory perception, and motility. Disruptions in ciliary function can lead to a diverse array of human diseases collectively termed ciliopathies. The positioning of Tmem218 within the ciliary transition zone suggests a critical role in maintaining proper ciliary composition and function, which has implications for understanding both normal physiology and pathological conditions.
Production and Properties of Recombinant Rat Tmem218
Recombinant Rat Tmem218 is produced through molecular cloning and expression techniques to generate pure protein samples for research purposes. The production typically involves inserting the Tmem218 gene sequence into expression vectors, transforming host cells, inducing protein expression, and purifying the expressed protein.
Commercial preparations of Recombinant Rat Tmem218 exhibit specific properties that are important for research applications. The table below summarizes the key specifications of commercially available Recombinant Rat Tmem218:
| Parameter | Specification |
|---|---|
| Size | 50 μg (other sizes available upon request) |
| Product Type | Recombinant Protein |
| Species | Rattus norvegicus (Rat) |
| UniProt Number | Q5U3Y9 |
| Expression Region | 1-115 (full length) |
| Tag Information | Determined during production process |
| Storage Buffer | Tris-based buffer, 50% glycerol (optimized) |
| Storage Conditions | -20°C (short-term), -20°C to -80°C (long-term) |
| Working Storage | 4°C for up to one week |
| Sequence Information | Full length protein |
The recombinant protein is typically stored in a specialized buffer containing Tris and glycerol, which helps maintain its stability and prevent degradation . Manufacturers recommend avoiding repeated freeze-thaw cycles, as these can compromise protein integrity and activity. For short-term use, working aliquots can be stored at 4°C for up to one week, while longer-term storage requires freezing at -20°C or -80°C .
The purity of commercially available recombinant proteins often exceeds 80%, making them suitable for a range of research applications including functional studies, antibody production, and protein-protein interaction analyses . This high level of purity ensures that experimental results are not confounded by the presence of contaminants or degradation products.
Functional Significance of Tmem218
The functional significance of Tmem218 has been primarily elucidated through studies of knockout mouse models, which have revealed critical roles in organ development and homeostasis. These studies provide valuable insights into the potential functions of rat Tmem218, given the high sequence homology between mouse and rat proteins.
Research by Gelfman et al. demonstrated that mice lacking Tmem218 develop polycystic kidneys, a condition characterized by the formation of fluid-filled cysts that can impair kidney function . Additionally, these knockout mice exhibit progressive retinal degeneration, with thinning of the outer nuclear layer (ONL) becoming apparent by 2 months of age, although no abnormalities were detected at 1 month of age. This temporal pattern suggests that Tmem218 plays a role in maintaining retinal integrity rather than in initial retinal development .
Interestingly, expression of Tmem218 was found to be downregulated in mice lacking functional androgen receptors, suggesting a potential hormone-dependent regulation mechanism. Furthermore, altered expression of genes involved in vitamin A metabolism was observed in these models, pointing to a possible role for Tmem218 in vitamin A homeostasis, which is crucial for normal vision .
At the molecular level, Tmem218 has been implicated in ciliary function, specifically within the transition zone of cilia. The transition zone serves as a selective barrier that regulates protein entry into the cilium, and Tmem218's localization to this compartment suggests a role in maintaining ciliary composition and function. Disruption of this regulatory function may underlie the pathological changes observed in kidney and retinal tissues of Tmem218-deficient mice.
Role in Ciliary Function and Disease
Recent research has established Tmem218 as a crucial component of the ciliary transition zone (TZ), a specialized compartment at the base of cilia that acts as a selective barrier between the ciliary and cytoplasmic compartments. This positioning is significant because cilia function as cellular antennae that detect and transduce various extracellular signals, and their proper function depends on a precisely regulated protein composition.
Studies have identified biallelic missense and nonsense mutations in the TMEM218 gene in patients with features related to Bardet-Biedl syndrome, Joubert syndrome, and Meckel-Gruber syndrome . These conditions belong to a spectrum of disorders collectively known as ciliopathies, which result from defects in ciliary structure or function and manifest with a diverse range of clinical features, including retinal degeneration, kidney abnormalities, and central nervous system malformations.
Molecular analyses have revealed that TMEM218 physically interacts with TMEM67/Meckelin, a member of the Meckel syndrome (MKS) module of the transition zone. This interaction was found to be significantly reduced by a missense mutation in TMEM218 identified in a patient with ciliopathy, providing a mechanistic explanation for the pathogenicity of this mutation . This finding highlights the importance of protein-protein interactions in the assembly and function of the ciliary transition zone.
Furthermore, functional studies in zebrafish (Danio rerio) have validated the pathogenicity of TMEM218 mutations and demonstrated genetic interactions with the nephronophthisis (NPHP) module, particularly with the Nphp4 component . These genetic interactions resulted in pronounced ciliopathy-related phenotypes, suggesting a synergistic relationship between TMEM218 and the NPHP module that is crucial for proper ciliary function. This synergistic interaction provides a molecular basis for understanding the variability in clinical manifestations observed in ciliopathy patients.
Expression Patterns and Tissue Distribution
The expression pattern of Tmem218 has been studied using various techniques, including LacZ immunohistochemistry in mouse models. These studies have revealed a broad distribution across multiple tissues and organs, suggesting diverse physiological functions.
In the eye, Tmem218 expression has been detected throughout various structures, including the retina, lens, ciliary body, and iris . This extensive ocular expression correlates with the retinal degeneration phenotype observed in Tmem218 knockout mice and suggests important roles in maintaining ocular health and function. The specific localization within different retinal cell types has not been fully characterized, but the development of retinal degeneration in knockout models suggests expression in photoreceptors or supporting cells.
Beyond the eye, Tmem218 expression has been documented in the kidney, brain, gastrointestinal tract, and adrenal gland . The expression in the kidney aligns with the polycystic kidney phenotype observed in knockout models, underscoring the protein's importance in renal physiology. The presence of Tmem218 in the brain and gastrointestinal tract suggests additional functions that have not been fully explored but may relate to the ciliopathy phenotypes observed in human patients with TMEM218 mutations.
Comparative Analysis of Tmem218 Across Species
Tmem218 exhibits significant sequence conservation across various species, suggesting evolutionary pressure to maintain its structure and function. This conservation provides valuable insights into the protein's fundamental biological importance and helps identify critical functional domains.
The rat Tmem218 protein shares approximately 85% sequence identity with its mouse counterpart and 81% with the human ortholog . This high degree of conservation, particularly across mammalian species, underscores the protein's fundamental biological importance and suggests that findings from rat studies may have relevance to human health and disease.
The conservation extends to the protein's domain architecture, with the transmembrane segments showing particularly high sequence similarity across species. This conservation pattern is typical for membrane-spanning domains, which often have structural constraints imposed by the lipid bilayer environment. In contrast, the connecting regions between the transmembrane segments may show more variability, potentially reflecting species-specific adaptations or functional specializations.
The cross-species functionality of Tmem218 has been demonstrated in studies using zebrafish models to validate the pathogenicity of human TMEM218 mutations . These studies highlight the utility of diverse animal models for understanding Tmem218 function and its role in disease, as well as the evolutionary conservation of ciliary transition zone components and their interactions.
Research Applications of Recombinant Rat Tmem218
Recombinant Rat Tmem218 serves as a valuable tool for various research applications aimed at understanding the protein's structure, function, and role in disease. These applications span a range of techniques and approaches in molecular and cellular biology.
One primary application is in the generation of antibodies against Tmem218, which can be used for protein detection in various assays. Commercially available antibodies, such as the TMEM218 Antibody (NBP1-90988) from Novus Biologicals, have been developed using recombinant proteins as immunogens and are applicable for immunocytochemistry, immunofluorescence, and immunohistochemistry in paraffin-embedded tissues . These antibodies enable the visualization of Tmem218 expression patterns in tissues and cells, providing insights into its distribution and potential functions.
Recombinant Tmem218 can also be employed in protein-protein interaction studies to identify binding partners and characterize molecular complexes. Techniques such as co-immunoprecipitation, pull-down assays, and yeast two-hybrid screens can utilize purified recombinant Tmem218 to elucidate its interaction network within the cell. Such studies have already revealed interactions with components of the ciliary transition zone, including TMEM67/Meckelin and the NPHP module .
Structural studies, including X-ray crystallography and nuclear magnetic resonance spectroscopy, may utilize recombinant Tmem218 to determine the protein's three-dimensional structure at atomic resolution. Such structural insights can inform the design of targeted therapeutics and provide a framework for understanding the functional impact of disease-associated mutations.
In disease modeling, recombinant Tmem218 variants harboring mutations identified in patients with ciliopathies can be generated to study the functional consequences of these mutations in vitro and in cell culture systems. Such studies can provide insights into the molecular mechanisms underlying disease pathogenesis and potentially guide the development of therapeutic interventions.
Product Specs
Note: We will prioritize shipping the format currently in stock. However, if you have a specific format requirement, please indicate it when placing your order, and we will prepare it accordingly.
Note: All proteins are shipped with standard blue ice packs by default. If you require dry ice shipping, please inform us in advance, as additional charges will apply.
Generally, the shelf life of liquid form is 6 months at -20°C/-80°C. The shelf life of lyophilized form is 12 months at -20°C/-80°C.
Target Background
Q&A
What is TMEM218 and what is its cellular localization?
TMEM218 is a transmembrane protein localized to the transition zone of the primary cilium, which serves as a partition between the cell body and the cilium. The primary cilium is a microtubule-based, antenna-like organelle that projects from the surface of most human cell types, allowing them to respond to extracellular signals . The transition zone is a known hotspot for ciliopathy-related proteins, indicating the critical role of this region in ciliary function . TMEM218 is embedded in the ciliary membrane with multiple transmembrane helices, including highly conserved regions at positions 44 and 115 that are essential for proper function .
What are the known functions of TMEM218?
TMEM218 functions primarily in maintaining the proper structure and function of the ciliary transition zone. This protein contributes to the partitioning of the cilium from the cell body, which is essential for proper ciliary signaling . Experimental evidence from mouse models suggests that TMEM218 plays a crucial role in the development and maintenance of retinal and renal tissues, as Tmem218-/- mice display progressive retinal degeneration and cystic kidney disease . The specific molecular mechanisms by which TMEM218 contributes to these processes remain an active area of investigation, but its evolutionary conservation across species underscores its fundamental importance in ciliary biology.
How is TMEM218 associated with human disease?
TMEM218 dysfunction has been linked to ciliopathies along the Joubert-Meckel syndrome spectrum. Exome sequencing of individuals with Joubert syndrome (JBTS) identified biallelic rare, predicted-deleterious variants in TMEM218 in multiple families . Clinical features associated with TMEM218 variants include the molar tooth sign (a characteristic brain malformation), occipital encephalocele, retinal dystrophy, polycystic kidneys, and polydactyly . Current evidence suggests that TMEM218 dysfunction accounts for approximately 0.16% of Joubert syndrome cases, making it a rare but significant contributor to the genetic landscape of ciliopathies .
What methods are used to identify TMEM218 variants in patients?
Researchers have employed several sequencing approaches to identify TMEM218 variants in patients with ciliopathies:
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Exome Sequencing: This has been the primary method used to identify novel TMEM218 variants. In one study, exome sequencing was performed on 53 individuals from a cohort of 655 families affected by JBTS who lacked pathogenic variants in known disease genes .
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Molecular Inversion Probes (MIPs): This targeted capture method has been used to screen for variants in known ciliopathy genes, including TMEM218 .
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Sanger Sequencing: This method is typically used to validate variants identified through next-generation sequencing approaches .
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Bioinformatic Analysis: After sequencing, variants are filtered based on frequency in population databases (excluding variants with MAF > 0.01), predicted pathogenicity using tools like SIFT, PolyPhen2, and MutationTaster, and adherence to ACMG 2015 guidelines for variant interpretation .
For rare disorders like TMEM218-related ciliopathies, collaborative platforms such as MatchMaker Exchange have proven valuable for identifying additional affected individuals across different research centers worldwide .
How can researchers generate and validate animal models for studying TMEM218 function?
Animal models, particularly mouse models, have been instrumental in understanding TMEM218 function. To generate and validate such models:
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Gene Knockout Strategies: Tmem218-/- mice have been generated to study the consequences of complete loss of TMEM218 function . These models allow researchers to observe phenotypes that develop over time, such as progressive retinal degeneration and cystic kidney disease.
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Recombinase-Driver Approaches: While not specifically mentioned for TMEM218 in the provided sources, techniques similar to those used for generating Th::Cre rat lines could be adapted . This would involve creating BAC transgenic rat lines with large genomic regulatory regions (200-300 Kb) controlling expression of recombinases .
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Phenotypic Validation: Validation involves thorough phenotypic characterization, including histological analysis of relevant tissues (retina, kidney, brain), functional assessments (electroretinography for retinal function), and molecular studies to confirm the absence of protein expression .
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Age-dependent Analysis: Since some phenotypes (like retinal degeneration) are progressive, analysis at multiple time points is essential. In Tmem218-/- mice, retinal changes were subtle at 14 weeks but pronounced by 29 weeks of age .
How do specific TMEM218 variants affect protein function and result in different clinical manifestations?
Research indicates that different TMEM218 variants may result in varying clinical severity, suggesting a potential genotype-phenotype correlation:
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Position-Specific Effects: Four of six families with TMEM218-related ciliopathies carry missense variants affecting the same highly conserved amino acid position 115 . This suggests this residue is particularly critical for protein function.
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Variant Severity Spectrum: Computational algorithms like CADD predict different levels of pathogenicity: p.Arg94*(40) > p.Arg115Cys(35) > p.Arg115His(27.9) > p.Gly44Val(26.9) . This aligns with clinical observations, as variants predicted to be less disruptive are found in individuals who survive into adulthood.
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Structural Implications: Bioinformatic tools like HOPE (Have Your Protein Explained) predict that missense variants disrupt protein function, particularly when they affect conserved residues in or adjacent to transmembrane alpha helices .
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Evolutionary Constraint: Aminode analysis shows that residues 44 and 115 are in highly conserved and evolutionarily constrained regions across orthologs, indicating their functional importance .
The mechanistic understanding of how these variants affect protein localization, interaction partners, or ciliary function remains incomplete and represents an important area for future research.
What is the relationship between TMEM218 and other ciliopathy-associated proteins?
TMEM218 functions within the complex protein network of the ciliary transition zone, but its specific interactions with other ciliopathy proteins remain to be fully elucidated:
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Transition Zone Complexes: Though not explicitly detailed in the available sources, TMEM218 likely interacts with other transition zone proteins. Future research using techniques such as proximity labeling or co-immunoprecipitation could identify these interaction partners.
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Functional Redundancy: The relatively low prevalence of TMEM218 mutations in ciliopathy cohorts (0.16% of Joubert syndrome cases) may reflect functional redundancy with other transition zone proteins .
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Pathway Integration: Further research is needed to determine where TMEM218 fits within known ciliopathy-associated pathways, such as the BBSome complex, NPHP complex, or MKS complex.
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Ciliary Signaling: Given the role of cilia in signal transduction, research into how TMEM218 dysfunction affects specific signaling pathways (e.g., Hedgehog, Wnt, PDGF) could provide insights into disease mechanisms.
What are the tissue-specific effects of TMEM218 dysfunction, and how do they contribute to the ciliopathy phenotype?
TMEM218 dysfunction appears to have particularly pronounced effects on specific tissues:
How can recombinant TMEM218 be utilized in structure-function studies?
Recombinant TMEM218 could be a valuable tool for understanding the structure-function relationship of this protein:
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Protein Structure Determination: Production of recombinant TMEM218 could facilitate structural studies using X-ray crystallography or cryo-electron microscopy, providing insights into the conformation of transmembrane helices and the effects of disease-causing variants.
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In Vitro Binding Assays: Recombinant TMEM218 could be used in binding assays to identify interaction partners within the ciliary transition zone, helping to establish its role in protein complexes.
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Variant Functional Analysis: Wild-type and mutant versions of recombinant TMEM218 could be compared in functional assays to determine how specific variants alter protein stability, localization, or interaction capabilities.
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Antibody Generation: Recombinant TMEM218 could be used to generate specific antibodies for immunolocalization studies, which would help determine the precise subcellular localization of the protein in different cell types and tissues.
What are potential therapeutic approaches for TMEM218-related ciliopathies?
While current treatments for ciliopathies are largely supportive, understanding TMEM218 function opens avenues for potential targeted therapies:
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Gene Therapy: Given the recessive nature of TMEM218-related ciliopathies, gene replacement strategies could potentially restore function. The relatively small size of the TMEM218 gene makes it amenable to packaging in viral vectors for delivery.
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Pharmacological Chaperones: For missense variants that affect protein folding but not intrinsic function, small molecules that stabilize the mutant protein could potentially restore function.
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Downstream Pathway Modulation: Identification of altered signaling pathways downstream of TMEM218 dysfunction could reveal targets for pharmacological intervention.
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Precision Medicine Approaches: The varying clinical manifestations associated with different TMEM218 variants suggest that personalized therapeutic approaches based on specific genetic variants may be necessary.
How can TMEM218 research inform our understanding of other ciliopathies?
Research on TMEM218 contributes to the broader understanding of ciliopathies in several ways:
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Transition Zone Biology: Insights into TMEM218 function enhance our understanding of the ciliary transition zone, a critical region implicated in numerous ciliopathies .
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Genotype-Phenotype Correlations: The spectrum of phenotypes associated with different TMEM218 variants provides a model for understanding how variant severity correlates with clinical manifestations in ciliopathies .
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Tissue-Specific Mechanisms: The preferential involvement of retina and kidney in TMEM218-related ciliopathies parallels patterns seen in other ciliopathies, suggesting common mechanisms of tissue vulnerability .
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Model Systems: The Tmem218-/- mouse model provides a valuable tool for testing therapeutic approaches that might be applicable to other ciliopathies with similar tissue involvement .
What are the challenges in expressing and purifying recombinant TMEM218 for in vitro studies?
Transmembrane proteins like TMEM218 present unique challenges for recombinant expression and purification:
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Expression Systems: Selection of appropriate expression systems is critical. While bacterial systems (E. coli) offer simplicity and high yield, eukaryotic systems (yeast, insect cells, mammalian cells) may be necessary for proper folding and post-translational modifications of TMEM218.
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Solubilization Strategies: As a multi-pass transmembrane protein, TMEM218 requires careful selection of detergents or lipid nanodiscs for solubilization while maintaining native conformation.
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Protein Stability: Transmembrane proteins often exhibit limited stability when removed from their native membrane environment. Addition of stabilizing agents or engineering of thermostable variants may be necessary.
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Functional Validation: Ensuring that recombinant TMEM218 retains its native conformation and function is essential. This may require development of specific functional assays relevant to its role in the ciliary transition zone.
What experimental approaches can be used to study TMEM218 localization and dynamics in ciliated cells?
Several advanced imaging and biochemical techniques can be employed to study TMEM218 in its native context:
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Super-resolution Microscopy: Techniques such as STORM, PALM, or STED microscopy can provide nanoscale resolution of TMEM218 localization within the ciliary transition zone, offering insights into its spatial relationship with other transition zone proteins.
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Live-cell Imaging: Fluorescently-tagged TMEM218 can be used to study its dynamics during ciliogenesis and in response to various stimuli, providing insights into its functional role.
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Proximity Labeling: Techniques such as BioID or APEX2 can identify proteins in close proximity to TMEM218 in living cells, helping to map its interaction network.
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FRAP (Fluorescence Recovery After Photobleaching): This technique can assess the mobility of TMEM218 within the transition zone membrane, providing insights into whether it functions as a static structural component or has dynamic roles.
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Correlative Light and Electron Microscopy (CLEM): This approach can connect the fluorescence localization of TMEM218 with ultrastructural features of the cilium, providing context for its function.
How conserved is TMEM218 across species, and what does this tell us about its function?
TMEM218 shows significant evolutionary conservation, suggesting fundamental importance in ciliary biology:
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Sequence Conservation: Analysis using tools like Aminode reveals that specific regions of TMEM218, particularly around residues 44 and 115, are in highly conserved and evolutionarily constrained regions across orthologs .
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Functional Conservation: The similar phenotypes observed in human patients with TMEM218 mutations and Tmem218-/- mice (retinal degeneration, kidney cysts) suggest functional conservation across mammals .
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Taxonomic Distribution: While specific details are not provided in the available sources, comprehensive analysis of TMEM218 across the tree of life could provide insights into when this protein emerged and which organisms rely on it for ciliary function.
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Structural Conservation: Comparative analysis of predicted transmembrane domains across species could indicate which structural features are most essential for function.
How does rat TMEM218 compare to human TMEM218 in terms of structure and function?
While specific comparisons between rat and human TMEM218 are not detailed in the available sources, general considerations for such comparisons include:
