Recombinant Danio rerio Solute carrier family 25 member 33 (slc25a33)

What is the molecular identity and classification of Danio rerio slc25a33?

Danio rerio slc25a33 is a protein-coding gene with Entrez Gene ID 406436. Its full name is "solute carrier family 25 (pyrimidine nucleotide carrier), member 33" and it has several synonyms including wu:fe01d11, zgc:65787, and zgc:77728 . The gene encodes a mitochondrial carrier protein that is part of the larger SLC25 family, which in humans comprises 53 members responsible for transporting various substrates across the inner mitochondrial membrane . The protein is 314 amino acids in length, as evidenced by the recombinant full-length protein sequence available for research applications .

What is the primary function of slc25a33 in zebrafish?

The slc25a33 protein functions as a specialized transporter for pyrimidine nucleotides across the inner mitochondrial membrane. Based on characterization of human SLC25A33, the zebrafish ortholog likely transports uracil, thymine, and cytosine (deoxy)nucleoside di- and triphosphates via an antiport mechanism . This function is critical for maintaining the nucleotide pool within mitochondria, which is essential for mitochondrial DNA replication and RNA synthesis. The protein's role makes it fundamentally important for proper mitochondrial function and, by extension, cellular energy metabolism in zebrafish .

How does slc25a33 compare with other members of the SLC25 family?

While slc25a33 specifically transports pyrimidine nucleotides, other members of the SLC25 family transport diverse substrates including inorganic anions, amino acids, carboxylates, various nucleotides, and coenzymes across the inner mitochondrial membrane . For example, SLC25A10 (also known as dicarboxylate carrier or DIC) can transport multiple substrates with different chemical properties, including succinate, phosphate, thiosulfate, and malate . Another example is SLC25A1, which functions as a citrate carrier and can mediate the exchange of malate, isocitrate, aconitate, and phosphoenolpyruvate in a 1:1 electroneutral ratio . This diversity highlights the specialized nature of slc25a33 within the broader context of mitochondrial transport proteins.

What are the optimal methods for expressing recombinant Danio rerio slc25a33?

For successful expression of recombinant Danio rerio slc25a33, the bacterial expression system using Escherichia coli has been demonstrated to be effective. The full-length protein (amino acids 1-314) can be expressed with an N-terminal histidine tag to facilitate purification . The expression construct should contain the complete coding sequence with appropriate bacterial promoters and ribosome binding sites optimized for E. coli expression. When designing expression vectors, researchers should consider codon optimization for E. coli, as disparate codon usage between zebrafish and bacteria may affect expression efficiency . Temperature, induction conditions (IPTG concentration), and growth media composition should be optimized to maximize protein expression while minimizing inclusion body formation, which can compromise proper folding of the membrane protein.

What purification strategies are most effective for recombinant slc25a33?

Purification of recombinant His-tagged slc25a33 typically involves:

• Cell lysis under conditions that solubilize membrane proteins (detergents)

• Immobilized metal affinity chromatography (IMAC) using the His-tag

• Additional purification steps such as ion-exchange or size-exclusion chromatography

The purified protein can be obtained at >90% purity as determined by SDS-PAGE . For storage, the protein can be lyophilized with a protective agent such as trehalose and stored in Tris/PBS-based buffer at pH 8.0. For long-term storage, it is recommended to add glycerol (5-50% final concentration) and store in aliquots at -20°C/-80°C to avoid repeated freeze-thaw cycles . Researchers should reconstitute the lyophilized protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL for experimental use .

How can researchers effectively measure transport activity of recombinant slc25a33?

Several complementary approaches can be used to measure the transport activity of recombinant slc25a33:

Liposome Reconstitution Assay:

The most direct approach involves reconstituting purified slc25a33 into liposomes that mimic the composition of the inner mitochondrial membrane. Cardiolipin, a dimeric lipid found in the inner mitochondrial membrane, may play an important role in the translocation mechanism and should be included in the liposome preparation . After reconstitution, researchers can measure the transport of radiolabelled pyrimidine nucleotides across the liposomal membrane. This requires careful selection of internal and external buffer conditions and precise timing of transport measurements .

Mitochondrial Swelling Assay:

While less direct, researchers can use isolated mitochondria for swelling assays. In this approach, the transport of an osmotically active compound causes water to enter mitochondria, leading to swelling that can be measured as a decrease in light scattering . For slc25a33, this would involve designing assays with appropriate cations that can cross the inner mitochondrial membrane to partner with the transported nucleotides .

Centrifugal Filtration:

For transport assays where selective inhibitors are not available, researchers can terminate transport by rapidly pelleting mitochondria or liposomes containing reconstituted slc25a33 via centrifugation. The presence of transported molecules can then be assayed in both the pellet and supernatant .

What are the substrate specificities of Danio rerio slc25a33 and how can they be determined?

Based on studies of human SLC25A33, the zebrafish ortholog likely transports uracil, thymine, and cytosine (deoxy)nucleoside di- and triphosphates via an antiport mechanism . To determine the exact substrate specificities of Danio rerio slc25a33, researchers should:

• Test transport of various pyrimidine nucleotides (UTP, CTP, TTP, UDP, CDP, TDP, etc.)

• Compare transport rates with purine nucleotides as controls

• Assess concentration-dependent transport to determine kinetic parameters (Km, Vmax)

• Examine the effect of potential inhibitors such as mercurial compounds, which have been shown to inhibit SLC25A33-catalyzed transport in human studies

These experiments should be conducted using reconstituted liposomes containing purified recombinant slc25a33 to provide the most accurate assessment of intrinsic transport properties.

How can researchers distinguish between transport activities of slc25a33 and other related carriers?

Distinguishing the transport activity of slc25a33 from other related carriers requires:

• Selective Inhibitors: If available, use carrier-specific inhibitors to block the activity of particular transporters.

• Substrate Specificity Profiling: Comprehensive testing of various substrates can reveal unique transport profiles. For example, while slc25a33 primarily transports pyrimidine nucleotides, it might handle certain substrates with different efficiencies compared to related carriers .

• Genetic Approaches: Express slc25a33 in systems lacking endogenous carriers, such as specific yeast mutants lacking mitochondrial carriers. Phenotype complementation can confirm the specific function of slc25a33 .

• Kinetic Analysis: Detailed kinetic parameters (Km, Vmax) for different substrates can create a "fingerprint" of transport activity that distinguishes between carriers.

• Transport Mechanism Analysis: Determining whether the carrier functions via antiport (exchange) or uniport mechanisms can help distinguish between carriers. For instance, human SLC25A33 operates via antiport while the related SLC25A36 can function via both uniport and antiport mechanisms .

How does zebrafish slc25a33 compare to its human ortholog?

Human SLC25A33 and zebrafish slc25a33 likely share significant functional similarities as mitochondrial pyrimidine nucleotide transporters. Human SLC25A33 has been characterized to transport uracil, thymine, and cytosine (deoxy)nucleoside di- and triphosphates via an antiport mechanism . Given the evolutionary conservation of essential mitochondrial functions, zebrafish slc25a33 likely performs similar transport activities.

Comparative studies between the human and zebrafish proteins could reveal:

• Differences in substrate affinities and transport kinetics

• Variations in regulatory mechanisms

• Potential differences in tissue-specific expression patterns

• Evolutionary adaptations specific to each species

Such comparative analyses would be valuable for researchers using zebrafish as a model organism for studying human mitochondrial diseases related to nucleotide transport defects.

What is the expression pattern of slc25a33 during zebrafish development?

While the provided search results don't contain specific information about slc25a33 expression patterns during zebrafish development, search result mentions a high-resolution mRNA expression time course of embryonic development in zebrafish (White RJ, Collins JE, et al.) . Researchers interested in slc25a33 developmental expression patterns could refer to this resource for detailed temporal expression data.

To fully characterize slc25a33 expression during development, researchers should consider:

• RNA-seq analysis across developmental stages

• In situ hybridization to localize expression in different tissues

• Quantitative PCR for stage-specific expression quantification

• Immunohistochemistry using antibodies against slc25a33 protein

Understanding the developmental expression pattern would provide insights into the stages and tissues where slc25a33 function is most critical.

What phenotypes result from slc25a33 depletion or mutation in zebrafish models?

Researchers investigating slc25a33 function in zebrafish could employ several approaches:

• Morpholino knockdown for transient depletion

• CRISPR/Cas9 genome editing for stable mutant lines

• Dominant-negative approaches using mutant forms of the protein

Phenotypic analysis should focus on:

• Mitochondrial function (oxygen consumption, ATP production)

• Mitochondrial DNA maintenance and replication

• Tissue-specific effects, particularly in high-energy demanding tissues

• Developmental defects, especially if slc25a33 is expressed during critical developmental periods

How can slc25a33 be used to study mitochondrial nucleotide transport in disease models?

Recombinant Danio rerio slc25a33 can serve as a valuable tool for studying mitochondrial nucleotide transport in disease contexts. Researchers can:

• Create disease-relevant mutations in recombinant slc25a33 corresponding to human disease variants

• Perform comparative transport studies between wild-type and mutant proteins

• Use reconstituted systems to screen for compounds that might restore function to mutant transporters

• Develop zebrafish models with slc25a33 mutations that mimic human disease conditions

This approach is particularly relevant since members of the SLC25 superfamily are responsible for 12 monogenic diseases in humans . Understanding the molecular mechanisms of slc25a33 function could provide insights into mitochondrial diseases caused by nucleotide transport defects.

What techniques are available for investigating slc25a33 interactions with other mitochondrial proteins?

Several techniques can be employed to investigate potential interactions between slc25a33 and other mitochondrial proteins:

• Co-immunoprecipitation: Using antibodies against slc25a33 to pull down potential interacting partners from mitochondrial lysates.

• Proximity Labeling: Techniques like BioID or APEX2, where slc25a33 is fused to a biotin ligase or peroxidase that biotinylates nearby proteins, allowing for their identification.

• Fluorescence Resonance Energy Transfer (FRET): Using fluorescently tagged slc25a33 and candidate interacting proteins to detect close proximity in living cells.

• Membrane Yeast Two-Hybrid: Specialized yeast two-hybrid systems designed for membrane proteins like slc25a33.

• Cross-linking Mass Spectrometry: Chemical cross-linking followed by mass spectrometry analysis to identify proteins in close proximity to slc25a33.

• Blue Native PAGE: Non-denaturing gel electrophoresis to identify native protein complexes containing slc25a33.

These techniques could reveal interactions with other components of mitochondrial nucleotide metabolism pathways, respiratory chain complexes, or other transport proteins.