Recombinant Pongo abelii Solute carrier family 25 member 44 (SLC25A44)
Description
The SLC25 Mitochondrial Carrier Family: An Overview
The SLC25 family comprises 53 identified members in the human genome, serving as critical transporters that facilitate the movement of various substrates across the inner mitochondrial membrane . These carriers are integral to numerous metabolic pathways, including the oxidation of fats and sugars, amino acid metabolism, iron-sulfur cluster synthesis, ion homeostasis, and mitochondrial macromolecular synthesis . The family shares common structural features and a unified transport mechanism that involves alternating access of the substrate-binding site to either side of the membrane .
Members of the SLC25 family transport a diverse array of compounds essential for mitochondrial function, including:
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Nucleotides (e.g., ADP/ATP via the adenine nucleotide translocase)
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Amino acids and their derivatives
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Carboxylic acids
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Fatty acids
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Cofactors
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Inorganic ions
Each carrier possesses specificity for particular substrates, enabling precise regulation of various metabolic processes within mitochondria. The well-studied mitochondrial ADP/ATP carrier exemplifies the family's importance, as it imports ADP into the mitochondrial matrix for ATP synthesis and exports newly synthesized ATP to the cytosol to fuel energy-requiring processes vital for cell survival .
Recombinant Production of Pongo abelii SLC25A44
Recombinant protein technology enables the production of specific proteins by inserting the corresponding genes into appropriate host organisms. For Pongo abelii SLC25A44, this approach allows for the isolation and detailed study of this mitochondrial carrier protein outside its native cellular environment.
Expression Systems
The production of recombinant Pongo abelii SLC25A44 has been documented using bacterial expression systems, particularly Escherichia coli. Available commercial sources offer recombinant full-length Pongo abelii SLC25A44 protein (residues 1-314) produced in E. coli with a His-tag for purification purposes.
The choice of E. coli as an expression host for SLC25A44 likely reflects several considerations:
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Cost-effectiveness and simplicity of bacterial culture systems
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Rapid growth and high protein yields
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Well-established protocols for membrane protein expression
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Suitability for structural and functional studies
Purification Strategies
The recombinant Pongo abelii SLC25A44 protein is typically produced with an affinity tag, such as a His-tag, to facilitate purification. The purification process for membrane proteins like SLC25A44 generally involves:
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Cell lysis to release expressed proteins
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Membrane fraction isolation
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Solubilization using appropriate detergents
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Affinity chromatography using the attached His-tag
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Further purification steps (e.g., size exclusion chromatography)
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Quality assessment of the purified protein
The resulting purified recombinant protein can then be used for various applications, including structural studies, functional characterization, and the development of screening assays.
Transmembrane Architecture
SLC25A44, like other members of the family, is predicted to contain:
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Six transmembrane α-helices with kinks at conserved proline residues
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A central substrate-binding site specific for BCAAs
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Two gates formed by salt-bridge networks on either side of the membrane
Substrate Binding and Specificity
The substrate specificity of SLC25A44 for BCAAs is determined by the nature of its binding site. While the specific residues involved in BCAA binding in SLC25A44 have not been fully characterized, it likely contains a conserved three-amino acid signature (V/I/L/AWW) on the cytosolic face of the transport cavity, which is characteristic of BCAA transporters.
The binding and transport of BCAAs by SLC25A44 involve a series of conformational changes that alternately expose the substrate-binding site to either the cytosolic or matrix side of the mitochondrial inner membrane, facilitating the directional movement of the substrates.
Functional Characterization of SLC25A44
Experimental evidence has established SLC25A44 as a mitochondrial BCAA carrier (MBC) that plays a crucial role in the import of branched-chain amino acids into the mitochondrial matrix for subsequent catabolism .
Transport Activity and Substrate Specificity
Functional studies, including those using Xenopus oocytes as expression systems, have demonstrated that SLC25A44 facilitates the transport of various compounds across membranes. Experimental data show significant transport activity for:
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Para-coumaric acid (14% increase, p=9.6×10^-3)
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Cinnamic acid (35% increase, p=5.4×10^-3)
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4-aminobenzoic acid (20% increase, p=2.7×10^-3)
More importantly, SLC25A44 has been shown to transport the BCAAs valine, leucine, and isoleucine, which serve as substrates for mitochondrial BCAA catabolism. This function is particularly significant in metabolically active tissues like brown adipose tissue (BAT).
Role in BCAA Metabolism
The transport of BCAAs into mitochondria via SLC25A44 is a crucial step in their catabolism. Once inside the mitochondrial matrix, BCAAs undergo deamination catalyzed by branched-chain amino acid aminotransferase 2 (BCAT2) to form branched-chain α-keto acids . These intermediates are further metabolized by the branched-chain α-keto acid dehydrogenase (BCKDH) complex.
Experiments using 13C-labeled, 15N-labeled leucine ([U-13C6, 15N1] Leu) have shown that disruption of SLC25A44 function significantly reduces the levels of leucine-derived metabolites, including α-ketoisocaproate (KIC), glutamate (Glu), and alanine (Ala) in brown adipocytes . This demonstrates the essential role of SLC25A44 in facilitating the entry of BCAAs into mitochondria for their metabolic processing.
Physiological Roles of SLC25A44
SLC25A44 contributes to several physiological processes through its role in BCAA transport and metabolism.
Thermogenesis and Metabolic Flexibility
One of the most significant physiological roles of SLC25A44 is in thermogenesis, particularly in brown adipose tissue. Studies have shown that mitochondrial BCAA oxidation in BAT is significantly enhanced during fever in response to pyrogenic mediators like prostaglandin E2 (PGE2) .
Experimental evidence indicates that genetic deletion of SLC25A44 in a BAT-specific manner blunts mitochondrial BCAA oxidation and non-shivering thermogenesis following PGE2 administration . This suggests that SLC25A44-mediated BCAA import into mitochondria is essential for optimal febrile responses.
Response to Environmental Challenges
SLC25A44 expression and activity are regulated in response to environmental challenges that require metabolic adaptation. Cold exposure and subsequent activation of β3-adrenoceptor signaling potently stimulate BAT thermogenesis and enhance the expression of genes involved in the mitochondrial BCAA catabolic pathway, including SLC25A44 .
Analysis of publicly available data (GSE51080) has indicated that chronic adaptation to cold temperatures (15°C for 2 weeks) potently stimulates the expression of SLC25A44 along with other components of the BCAA catabolic pathway and BAT thermogenic genes like UCP1 and PPARGC1A .
Experimental Data and Research Findings
Research on SLC25A44 has yielded valuable insights into its function and physiological significance. Key experimental findings include:
Impact of SLC25A44 Deletion
BAT-specific deletion of SLC25A44 in mice (Ucp1-Cre × Slc25a44 flox/flox) has provided insights into its role in BCAA metabolism and thermogenesis . While this deletion did not alter body weight or tissue mass of metabolic organs, it significantly reduced valine oxidation by approximately 70% in BAT, reinforcing the requirement of SLC25A44 for mitochondrial BCAA oxidation in vivo .
This impairment in BCAA oxidation has functional consequences, as demonstrated by the reduced thermogenic response in SLC25A44 knockout mice following PGE2 administration.
Cellular Metabolic Effects
At the cellular level, SLC25A44 is required for:
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Mitochondrial BCAA deamination
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Synthesis of mitochondrial amino acids
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Production of TCA cycle intermediates
GC-MS analysis of intracellular metabolites has revealed that levels of leucine, α-ketoisocaproate, alanine, and glutamate are significantly lower in SLC25A44-knockout brown adipocytes compared to wild-type control cells . This reflects the reduced conversion of leucine to downstream metabolites when SLC25A44-mediated transport is impaired.
Table 1: Metabolite Levels in Wild-Type vs. SLC25A44 Knockout Brown Adipocytes
| Metabolite | Wild-Type | SLC25A44 KO | Statistical Significance |
|---|---|---|---|
| Leucine | Higher | Lower | p < 0.05 |
| α-Ketoisocaproate (KIC) | Higher | Lower | p < 0.05 |
| Alanine | Higher | Lower | p < 0.05 |
| Glutamate | Higher | Lower | p < 0.05 |
| Aspartate | Higher | Lower | Not significant |
Comparative Analysis: Human vs. Pongo abelii SLC25A44
The SLC25A44 protein is well-conserved between humans and orangutans, reflecting their evolutionary relationship with approximately 97% DNA sequence similarity. This conservation suggests functional similarities in their respective roles in BCAA transport and metabolism.
Functional Conservation
The functional attributes of SLC25A44 are likely conserved between humans and orangutans due to the essential nature of BCAA metabolism across mammals. Both proteins are expected to:
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Localize primarily to the inner mitochondrial membrane
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Transport BCAAs into the mitochondrial matrix
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Support mitochondrial BCAA catabolism
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Contribute to energy metabolism and thermogenesis
The conservation of these functions across species underscores the fundamental importance of SLC25A44 in cellular metabolism.
Research Applications and Future Directions
Recombinant Pongo abelii SLC25A44 offers valuable research opportunities for advancing our understanding of mitochondrial BCAA transport and its implications for metabolic health.
Current Research Applications
Recombinant SLC25A44 protein can be utilized for:
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Structural studies to elucidate the precise mechanism of BCAA transport
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Development of screening assays for potential modulators of BCAA metabolism
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Comparative studies to understand species-specific variations in mitochondrial function
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Investigation of metabolic disorders associated with altered BCAA metabolism
Future Research Directions
Several promising avenues for future research on SLC25A44 include:
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Detailed structural characterization through crystallography or cryo-electron microscopy
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Comprehensive analysis of regulatory mechanisms controlling SLC25A44 expression and activity
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Investigation of potential roles in diseases associated with mitochondrial dysfunction
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Exploration of therapeutic approaches targeting SLC25A44 for metabolic disorders
As research on SLC25A44 continues to evolve, a more complete understanding of its structure, function, and physiological significance will emerge, potentially revealing new therapeutic targets for diseases involving altered BCAA metabolism.
Product Specs
Note: We prioritize shipping the format currently in stock. However, if you have specific format requirements, please indicate them during order placement, and we will accommodate your request.
Note: All our proteins are shipped with standard blue ice packs. If dry ice shipping is required, please communicate with us beforehand, as additional fees 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
KEGG: pon:100172017
UniGene: Pab.699
Q&A
Structural and Functional Characterization
Q: What is the basic function of SLC25A44 in Pongo abelii mitochondria?
A: SLC25A44 in Pongo abelii likely functions as a mitochondrial branched-chain amino acid carrier (MBC) responsible for transporting essential BCAAs (valine, leucine, and isoleucine) across the inner mitochondrial membrane. Based on studies in rodents, this protein plays a crucial role in metabolic flexibility during stress adaptation by facilitating BCAA entry into mitochondria for catabolic processes . The transport function enables mitochondrial BCAA deamination and subsequent utilization of these amino acids in the TCA cycle. To confirm this function in Pongo abelii specifically, researchers would need to conduct mitochondrial transport assays using recombinant protein expressed in a suitable system, followed by functional characterization through techniques such as isotope-labeled BCAA tracking experiments.
Q: How does the protein structure of Pongo abelii SLC25A44 compare to that of humans and other primates?
A: While specific structural data for Pongo abelii SLC25A44 is limited in current literature, researchers should approach this question through comparative sequence analysis and protein modeling. SLC25A44 belongs to the mitochondrial carrier family characterized by three tandem repeats of approximately 100 amino acids, each containing two transmembrane domains. Homology modeling using the human SLC25A44 as a template would reveal potential structural differences that might affect substrate specificity or transport kinetics. Key structural features to examine include the substrate binding pocket, transmembrane regions, and matrix-facing domains. Differences in conserved motifs could indicate functional adaptations specific to orangutan metabolism.
Expression Patterns and Regulation
Q: What tissues in Pongo abelii express SLC25A44 at the highest levels, and how can this be determined?
A: Based on rodent studies, SLC25A44 shows significant expression in metabolically active tissues, particularly brown adipose tissue (BAT) . To determine tissue-specific expression patterns in Pongo abelii, researchers should employ a combination of:
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qRT-PCR analysis of RNA extracted from various orangutan tissues (when ethically available through conservation programs)
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Immunohistochemistry using specific antibodies against Pongo abelii SLC25A44
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RNA-seq data analysis from existing orangutan tissue databases
Conservation status of Pongo abelii presents ethical limitations for tissue sampling, so researchers should prioritize non-invasive approaches or utilize samples collected during veterinary procedures. Comparative analysis with expression data from other primates can provide additional context for interpreting results.
Metabolic Role and Adaptation
Q: How does SLC25A44 function contribute to metabolic flexibility in Pongo abelii compared to other primates?
A: SLC25A44's role in metabolic flexibility likely varies across primates based on their evolutionary adaptations to different environments and dietary patterns. In rodents, SLC25A44-mediated mitochondrial BCAA import is significantly enhanced during fever and psychological stress . For Pongo abelii, researchers should investigate:
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Relative expression levels across tissues compared to other primates
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Kinetic properties of the transporter using recombinant protein in reconstituted liposomes
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Responsiveness to environmental stressors specific to orangutan habitat (temperature variations, food availability fluctuations)
A particularly interesting approach would be to measure oxygen consumption rates in cells expressing Pongo abelii SLC25A44 versus human SLC25A44 under various metabolic challenges. This could reveal species-specific adaptations in the protein's function that correspond to the orangutan's unique arboreal lifestyle and feeding patterns.
Q: What role might SLC25A44 play in thermoregulation in Pongo abelii, particularly given the absence of classic brown adipose tissue in adult great apes?
A: Studies in rodents demonstrate that SLC25A44 (MBC) is essential for mitochondrial BCAA oxidation and non-shivering thermogenesis in brown adipose tissue during fever response . While adult great apes, including orangutans, lack classic brown adipose tissue, SLC25A44 may still contribute to metabolic adaptation through:
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Activity in beige/recruitable adipocytes that express UCP1 under specific conditions
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Alternative thermogenic pathways in muscle tissue
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General metabolic flexibility during environmental stress
Researchers should design experiments comparing the thermogenic capacity of cells expressing Pongo abelii SLC25A44 versus SLC25A44 from cold-adapted mammals. Oxygen consumption measurements in the presence of different BCAA substrates would help quantify potential differences in metabolic efficiency.
Experimental Design Considerations
Q: What controls are essential when investigating recombinant Pongo abelii SLC25A44 function in heterologous expression systems?
A: When designing experiments with recombinant Pongo abelii SLC25A44, researchers must implement several critical controls:
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Empty vector controls to account for background transport activity
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Human SLC25A44 as a comparison for primate-specific functions
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Site-directed mutagenesis controls targeting conserved residues to verify functional domains
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Substrate specificity controls using structurally similar non-BCAA compounds
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Transport assays with and without membrane potential to confirm energy dependence
Additionally, researchers should include both positive controls (known mitochondrial transporters like the ADP/ATP carrier) and negative controls (non-functional mutants) to validate assay conditions. When using cell-based assays, confirmation of proper mitochondrial localization through confocal microscopy is essential before interpreting functional data.
Recombinant Protein Production
Q: What expression system is optimal for producing functional recombinant Pongo abelii SLC25A44?
A: For functional recombinant Pongo abelii SLC25A44 production, researchers should consider several expression systems, each with specific advantages:
| Expression System | Advantages | Limitations | Optimization Strategies |
|---|---|---|---|
| E. coli | High yield, cost-effective, rapid expression | Potential improper folding of membrane proteins, lack of post-translational modifications | Use specialized strains (C41/C43), fusion tags (MBP, SUMO), low temperature induction |
| Insect cells | Better membrane protein folding, some post-translational modifications | Moderate yield, more complex cultivation | Optimize codon usage, use strong viral promoters, screen multiple cell lines |
| Mammalian cells | Native-like folding, proper post-translational modifications | Lower yield, expensive, time-consuming | Use stable cell lines, inducible expression systems, optimize transfection protocols |
| Cell-free systems | Rapid, avoids toxicity issues | Lower yield, expensive reagents | Supplement with chaperones and lipids, optimize redox conditions |
For mitochondrial carriers like SLC25A44, insect cell expression systems often provide the best balance between yield and functionality. Researchers should include a purification tag (His or FLAG) and verify protein integrity by circular dichroism spectroscopy before functional studies.
Functional Assays
Q: What are the most reliable assays for measuring BCAA transport activity of recombinant Pongo abelii SLC25A44?
A: Several complementary approaches should be employed to reliably measure BCAA transport activity:
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Reconstituted Liposome Transport Assays: Purified recombinant SLC25A44 can be reconstituted into liposomes, and transport activity measured using radiolabeled BCAAs. This system allows precise control of internal and external environments and can determine kinetic parameters (Km, Vmax).
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Mitochondrial Uptake Experiments: Using isolated mitochondria from cells expressing recombinant Pongo abelii SLC25A44, researchers can measure BCAA uptake rates with either radiolabeled substrates or through metabolite analysis by LC-MS/MS.
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Cellular Respiration Measurements: As demonstrated in rodent studies, oxygen consumption rate (OCR) can be measured using instruments like the Seahorse XFe Analyzer to assess BCAA-dependent respiration in cells expressing SLC25A44 .
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Isotope Tracing Experiments: Using 13C-labeled BCAAs, researchers can trace the metabolic fate of transported amino acids through metabolomics approaches.
Each method provides different insights into transporter function, and triangulation of results from multiple assays increases confidence in findings.
Evolutionary Context
Q: How has SLC25A44 evolved across primate lineages, and what functional implications might these differences have?
A: To address this question, researchers should perform comprehensive phylogenetic analysis of SLC25A44 sequences across primates, with particular attention to:
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Selection pressure analysis (dN/dS ratios) to identify positively selected residues
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Mapping of amino acid changes onto structural models to predict functional impacts
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Correlation of sequence variations with ecological and dietary adaptations
The arboreal lifestyle and primarily frugivorous diet of Pongo abelii may have driven specific adaptations in metabolic pathways, potentially reflected in SLC25A44 function. Comparative functional studies using recombinant proteins from multiple primate species would reveal whether sequence differences translate to altered transport properties. Researchers should focus on regions that interact directly with BCAAs or regulate transport activity when analyzing evolutionary changes.
Disease Models and Conservation
Q: How might studying Pongo abelii SLC25A44 contribute to understanding metabolic disorders in humans?
A: Comparative studies of SLC25A44 across species provide valuable insights into fundamental aspects of BCAA metabolism that may be relevant to human metabolic disorders. Researchers should focus on:
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Identifying conserved functional domains essential across species versus adaptable regions
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Characterizing how variations in SLC25A44 correlate with metabolic parameters across primates
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Developing functional assays that can distinguish between normal and pathological variants
The evolutionary distance between humans and orangutans provides a useful comparative framework for distinguishing essential functions from species-specific adaptations. This information can help prioritize variants of unknown significance identified in human genetic studies of metabolic diseases.
Ethical and Conservation Implications
Q: What ethical considerations should guide research on genes from critically endangered species like Pongo abelii?
A: Research involving genetic material from critically endangered species requires stringent ethical frameworks:
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All studies should contribute directly or indirectly to conservation efforts
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Use existing biological repositories or non-invasive sampling methods whenever possible
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Obtain appropriate permits from conservation authorities and follow CITES regulations
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Share data openly to maximize research benefits while minimizing need for additional sampling
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Consider how research findings might benefit the species' conservation
For Pongo abelii, with an estimated wild population of only about 6,600 individuals , researchers should prioritize non-invasive methods and collaborate closely with orangutan conservation programs. Emphasis should be placed on how understanding SLC25A44 function might contribute to health monitoring or management of captive breeding programs.
