Recombinant Macaca fascicularis Mitochondrial thiamine pyrophosphate carrier (SLC25A19)

What is SLC25A19 and what is its fundamental role in mitochondrial function?

SLC25A19 is a mitochondrial carrier protein that primarily functions to transport thiamine pyrophosphate (TPP) across the inner mitochondrial membrane. As a member of the mitochondrial carrier family, it plays a crucial role in energy metabolism by ensuring the availability of TPP, an essential cofactor for several mitochondrial enzymes. The protein shuttles TPP from the cytosol into the mitochondrial matrix, where TPP serves as a cofactor for key enzymes involved in carbohydrate metabolism and energy production .

The main function of SLC25A19 involves the exchange of cytosolic TPP with mitochondrial ATP and/or ADP, creating a balanced transport system that maintains appropriate concentrations of these vital molecules across mitochondrial compartments . This exchange mechanism is fundamental to maintaining optimal mitochondrial function and cellular energy production.

How conserved is the SLC25A19 gene across species, and what can we learn from comparative studies with Macaca fascicularis?

SLC25A19 is highly conserved across species, reflecting its essential role in cellular metabolism. Comparative studies between human, yeast, Drosophila, and primate SLC25A19 orthologs reveal significant structural and functional similarities. For instance, the Drosophila melanogaster thiamine pyrophosphate carrier (DmTpc1p) shows functional similarity to human SLC25A19, as evidenced by cross-species complementation studies where DmTpc1p expression rescued growth defects in Saccharomyces cerevisiae TPC1 null mutants .

In the case of Macaca fascicularis (cynomolgus monkey), the SLC25A19 protein shares approximately 98% amino acid sequence identity with human SLC25A19, making it an excellent model for studying human TPP transport mechanisms and related pathologies. This high degree of conservation suggests that research findings from cynomolgus monkey models would likely translate effectively to human applications, particularly for understanding disease mechanisms and developing therapeutic interventions.

What are the known substrates of SLC25A19 besides thiamine pyrophosphate?

While SLC25A19's primary substrate is thiamine pyrophosphate, reconstitution studies have demonstrated that it can also transport other molecules, albeit with lower efficiency. Research with reconstituted DmTpc1p, a homolog of SLC25A19, has shown that it can transport several other substrates including:

• Pyrophosphate

• ADP

• ATP

• Other nucleotides

The transport capacity follows this order of efficiency: thiamine pyrophosphate > pyrophosphate > nucleotides (ADP/ATP) . This substrate preference pattern is likely conserved in Macaca fascicularis SLC25A19 as well, given the high degree of evolutionary conservation of this carrier protein.

What are the optimal expression systems for recombinant Macaca fascicularis SLC25A19 production?

Based on successful approaches with homologous proteins, the following expression systems are recommended for recombinant Macaca fascicularis SLC25A19 production:

Bacterial Expression Systems:
Bacterial systems, particularly E. coli, have been successfully used for the expression of mitochondrial carrier proteins. For instance, DmTpc1p was effectively over-expressed in bacteria, purified, and reconstituted into liposomes for functional studies . For Macaca fascicularis SLC25A19, the following protocol can be adapted:

• Clone the full-length SLC25A19 coding sequence into an expression vector with an appropriate tag (His-tag is commonly used)

• Transform into E. coli BL21(DE3) or similar expression strains

• Induce expression with IPTG at lower temperatures (16-20°C) to enhance proper folding

• Extract and purify the protein using affinity chromatography

Yeast Expression Systems:
Saccharomyces cerevisiae offers advantages for functional expression of mitochondrial carriers, as demonstrated by complementation studies with DmTpc1p in S. cerevisiae TPC1 null mutants :

• Use a yeast expression vector with a strong promoter (e.g., GAL1)

• Transform into S. cerevisiae strains lacking endogenous TPC1

• Culture in selective media with appropriate carbon sources

• Verify expression by Western blotting and functional complementation

Mammalian Cell Expression Systems:
For studies requiring post-translational modifications similar to in vivo conditions:

• Clone SLC25A19 into mammalian expression vectors

• Transfect into HEK293T or CHO cells

• Select stable transfectants for consistent expression

• Verify correct mitochondrial localization using fluorescent tags or immunostaining

How can the transport activity of recombinant SLC25A19 be measured in vitro?

The gold standard method for measuring the transport activity of mitochondrial carriers is the liposome reconstitution assay, as demonstrated with DmTpc1p . The following protocol can be adapted for Macaca fascicularis SLC25A19:

Liposome Reconstitution Assay:

• Liposome Preparation:

  • Prepare liposomes using a mixture of phospholipids (e.g., egg phosphatidylcholine and cardiolipin)

  • Form unilamellar vesicles by extrusion or sonication

  • Incorporate purified recombinant SLC25A19 protein into liposomes

• Transport Measurement:

  • Preload liposomes with specific internal substrates (e.g., ATP/ADP)

  • Initiate transport by adding external substrate (e.g., radiolabeled TPP)

  • At timed intervals, terminate transport using specific inhibitors

  • Separate liposomes from external medium by gel filtration or filtration

  • Quantify transported molecules using scintillation counting for radiolabeled substrates

• Kinetic Analysis:

  • Determine transport rates at varying substrate concentrations

  • Calculate kinetic parameters (Km, Vmax) using appropriate models

  • Compare transport efficiency with different substrates

Example Transport Parameters Based on DmTpc1p Studies:

Note: Values are extrapolated from DmTpc1p studies and may vary for Macaca fascicularis SLC25A19

What methods are most effective for studying SLC25A19 localization and interactions in mitochondria?

Several complementary approaches can be used to study SLC25A19 localization and interactions:

Subcellular Fractionation and Western Blotting:

• Isolate intact mitochondria from cells expressing recombinant SLC25A19

• Separate outer and inner mitochondrial membrane fractions

• Perform Western blot analysis using anti-SLC25A19 antibodies

• Include markers for different mitochondrial compartments as controls

Fluorescence Microscopy:

• Generate fusion constructs with fluorescent tags (e.g., GFP)

• Express in relevant cell lines and visualize using confocal microscopy

• Co-stain with mitochondrial markers (e.g., MitoTracker)

• Perform co-localization analysis

Protein-Protein Interaction Studies:

• Co-immunoprecipitation (Co-IP):

  • Use antibodies against SLC25A19 to pull down interacting proteins

  • Identify binding partners by mass spectrometry

• Proximity Labeling (BioID or APEX):

  • Fuse SLC25A19 to a proximity labeling enzyme

  • Express in cells and activate labeling

  • Identify proximal proteins by pull-down and mass spectrometry

• Crosslinking Mass Spectrometry (XL-MS):

  • Apply chemical crosslinkers to capture transient interactions

  • Digest and analyze crosslinked peptides by mass spectrometry

How do mutations in SLC25A19 affect its transport function and what methodologies best characterize these effects?

Mutations in SLC25A19 can significantly affect its transport function, typically resulting in reduced TPP transport into mitochondria. Several methodologies can characterize these functional impacts:

Liposome Reconstitution Assays:
As described earlier, this approach can directly measure transport activity of wild-type versus mutant SLC25A19 proteins. Key parameters to measure include:

• Initial transport rates

• Substrate affinity (Km)

• Maximum transport capacity (Vmax)

• Substrate specificity profiles

Yeast Complementation Assays:
Expressing mutant variants in S. cerevisiae TPC1 null mutants allows functional assessment based on growth phenotypes:

• Transform TPC1-deficient yeast with wild-type or mutant SLC25A19

• Assess growth rates on fermentable carbon sources

• Quantify growth defects as a measure of functional impairment

Mitochondrial Function Assessment in Cell Models:
For mutations identified in patients with thiamine metabolism dysfunction syndrome 4 (THMD4), the following parameters can be measured:

Example of Mutation Effects:
Recent functional studies on SLC25A19 variants causing THMD4 demonstrated significant decreases in mitochondrial TPP levels . Four novel heterozygous variations were characterized:

• c.169G>A (p.Ala57Thr)

• c.383C>T (p.Ala128Val)

• c.76G>A (p.Gly26Arg)

• c.745T>A (p.Phe249Ile)

All these variants showed impaired TPP transport activity when compared to wild-type SLC25A19 .

What is the relationship between SLC25A19 mutations and clinical phenotypes such as thiamine metabolism dysfunction syndrome 4?

SLC25A19 mutations cause thiamine metabolism dysfunction syndrome 4 (THMD4, OMIM #613710), an autosomal recessive disorder with distinct clinical manifestations:

Core Clinical Features of THMD4:

• Bilateral striatal degradation

• Progressive polyneuropathy

• Episodic encephalopathy triggered by febrile illness

• Fever of unknown origin as an early presentation

Genotype-Phenotype Correlations:
The relationship between specific SLC25A19 mutations and clinical severity is becoming clearer through functional studies. Mutations that severely impair TPP transport (such as truncating mutations) generally correlate with earlier onset and more severe manifestations. Milder mutations (such as some missense variants that retain partial function) may present with later onset or attenuated symptoms.

In a study of patients with THMD4, compound heterozygous variations in SLC25A19 (including c.169G>A, c.383C>T, c.76G>A, and c.745T>A) were associated with encephalopathy with basal ganglia signal changes following fever . Functional studies confirmed that these variants significantly reduced mitochondrial TPP levels, establishing a direct link between impaired transport activity and clinical presentation.

Molecular Mechanisms of Pathogenesis:

• Reduced TPP transport impairs activity of mitochondrial TPP-dependent enzymes

• This leads to compromised energy metabolism, particularly in high-energy demanding tissues like the brain

• Disruption of energy metabolism in basal ganglia neurons results in striatal degeneration

• Peripheral nerves are also affected, leading to polyneuropathy

What approaches can be used to screen novel SLC25A19 variants for pathogenicity?

A comprehensive approach to screen SLC25A19 variants for pathogenicity involves multiple complementary methods:

Computational Prediction Tools:

• Sequence conservation analysis across species

• Protein structure prediction and modeling of mutation effects

• Use of prediction algorithms (SIFT, PolyPhen, CADD, etc.)

• Evaluation of alternative splicing effects for intronic or splice-site variants

Functional Validation Assays:

Integrated Pathogenicity Classification Framework:

This framework, as demonstrated in the study of novel SLC25A19 variants , enables robust classification of variants as pathogenic, likely pathogenic, variant of uncertain significance (VUS), likely benign, or benign.

How can Macaca fascicularis SLC25A19 be utilized as a model for human disease research?

Macaca fascicularis SLC25A19 offers several advantages as a model for human disease research:

Evolutionary Proximity and Translational Value:
The high sequence homology (approximately 98%) between cynomolgus monkey and human SLC25A19 makes it an excellent model for studying human disorders. This close evolutionary relationship means that findings in Macaca fascicularis are more likely to translate effectively to human applications compared to rodent or other models.

Development of Disease Models:
Cynomolgus monkeys with modified SLC25A19 could be generated using targeted genome editing approaches:

• CRISPR/Cas9-mediated gene editing:

  • Introduction of specific patient mutations

  • Creation of hypomorphic alleles to model partial loss of function

  • Complete knockout to study null phenotypes

As mentioned in the search results, researchers have successfully generated a cynomolgus monkey carrying biallelic mutations in microcephaly-related genes using transcription activator-like effector nucleases (TALENs) . Similar approaches could be applied to SLC25A19.

Applications in Therapeutic Development:
Macaca fascicularis SLC25A19 models could facilitate:

• Testing of TPP supplementation regimens and delivery methods

• Evaluation of small molecule enhancers of TPP transport

• Development of gene therapy approaches

• Validation of biomarkers for monitoring treatment efficacy

Advantages for Neurological Research:
Since THMD4 primarily affects the central and peripheral nervous systems, the closer neuroanatomical and physiological similarity between primates and humans (compared to other model organisms) provides significant advantages for studying disease mechanisms and treatments.

What is known about the structure-function relationship of SLC25A19 and how can this inform drug development?

While detailed structural information specifically for Macaca fascicularis SLC25A19 is limited, insights can be derived from homology modeling based on related mitochondrial carriers and functional studies:

Predicted Structural Features:
SLC25A19, like other mitochondrial carriers, likely contains:

• Six transmembrane helices forming a barrel-like structure

• A central substrate translocation pathway

• Characteristic mitochondrial carrier family signature motifs

• Substrate binding sites that recognize TPP structural features

Structure-Function Insights from Mutations:
Analysis of disease-causing mutations provides valuable information about critical functional regions:

• Mutations in transmembrane domains often disrupt protein folding or stability

• Mutations in substrate-binding regions typically affect transport kinetics

• Mutations at dimer interfaces may impair oligomerization

The four novel SLC25A19 variants identified in THMD4 patients (p.Ala57Thr, p.Ala128Val, p.Gly26Arg, and p.Phe249Ile) offer insights into regions critical for TPP transport . Functional characterization of these variants revealed impaired TPP transport activity, highlighting the importance of these residues.

Implications for Drug Development:
Understanding the structure-function relationship can guide therapeutic strategies:

• TPP Analogs with Enhanced Transport:

  • Design of TPP derivatives that maintain cofactor activity but exhibit improved transport by mutant SLC25A19

• Allosteric Activators:

  • Identification of small molecules that bind to SLC25A19 and enhance residual transport activity of mutant proteins

• Protein Stabilizers:

  • For mutations that primarily affect protein stability, chemical chaperones might restore functional expression

• Alternative Transport Pathways:

  • Identification of other transporters that might be enhanced to compensate for SLC25A19 dysfunction

What methodological approaches can overcome challenges in studying membrane proteins like SLC25A19?

Studying membrane proteins like SLC25A19 presents unique challenges due to their hydrophobic nature and complex native environment. Several advanced methodologies can address these challenges:

Stabilization Strategies for Structural Studies:

• Nanodiscs and Lipid Nanodiscs:

  • Incorporation of SLC25A19 into nanodiscs provides a native-like lipid environment

  • Enables structural studies while maintaining protein stability

• Antibody Fragment Stabilization:

  • Use of Fab fragments or nanobodies to stabilize specific conformations

  • Facilitates crystallization or cryo-EM analysis

• Fusion Protein Approaches:

  • Fusion with stable soluble proteins (e.g., T4 lysozyme)

  • Increases solubility while preserving function

Advanced Structural Techniques:

• Cryo-Electron Microscopy (Cryo-EM):

  • Allows visualization of proteins in near-native environments

  • Does not require crystallization

  • Can capture different conformational states

• Solid-State NMR:

  • Provides atomic-level information about membrane proteins

  • Can be performed in lipid environments

• Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS):

  • Maps protein dynamics and ligand-binding sites

  • Less demanding in terms of sample quantity and purity

Functional Characterization Approaches:

• Single-Molecule Transport Assays:

  • Using fluorescent substrates to track individual transport events

  • Provides insights into transport mechanism and kinetics

• Patch-Clamp of Reconstituted Proteins:

  • Direct electrophysiological measurement of transport activity

  • High temporal resolution for kinetic studies

• Microscale Thermophoresis (MST):

  • Measures binding affinities in solution with minimal sample consumption

  • Can be used to screen potential ligands or inhibitors

Computational Methods:

• Molecular Dynamics Simulations:

  • Predicts protein behavior in lipid bilayers

  • Models substrate binding and translocation pathways

• Deep Learning Approaches:

  • Predicts protein structures from sequence information

  • Models protein-ligand interactions for drug discovery

How does SLC25A19 function relate to broader cellular metabolic networks?

SLC25A19's role extends beyond simple TPP transport, intersecting with multiple metabolic pathways:

Integration with Energy Metabolism:
TPP is a critical cofactor for several key enzymes involved in cellular energy production:

• Pyruvate dehydrogenase complex (PDH)

• α-ketoglutarate dehydrogenase complex (KGDH)

• Branched-chain α-keto acid dehydrogenase complex (BCKDH)

SLC25A19 dysfunction therefore impacts multiple metabolic pathways simultaneously, explaining the complex clinical manifestations of THMD4. Impaired activity of these enzymes leads to:

• Disrupted TCA cycle function

• Altered amino acid metabolism

• Compromised mitochondrial energy production

Role in Redox Balance:
TPP-dependent enzymes also influence cellular redox state:

• Altered NADH/NAD+ ratios due to decreased PDH and KGDH activity

• Potential downstream effects on reactive oxygen species (ROS) production

• Implications for mitochondrial antioxidant defense mechanisms

Cross-talk with Other Metabolic Transporters:
SLC25A19 likely functions within a network of mitochondrial transporters that collectively regulate mitochondrial metabolism. Research is needed to understand how SLC25A19 activity is coordinated with other transporters to maintain metabolic homeostasis.

What are the species-specific differences in SLC25A19 function between humans and Macaca fascicularis?

While the high sequence homology suggests similar function, subtle species-specific differences may exist between human and Macaca fascicularis SLC25A19:

Potential Differences to Investigate:

• Transport Kinetics:

  • Slight variations in substrate affinity (Km) or maximum transport rate (Vmax)

  • Differences in substrate preference hierarchies

  • Temperature or pH sensitivity profiles

• Regulatory Mechanisms:

  • Species-specific post-translational modifications

  • Differences in transcriptional regulation

  • Variations in protein-protein interactions affecting activity or localization

• Physiological Adaptations:

  • Adaptations related to dietary differences between species

  • Metabolic rate considerations and energy demand differences

  • Environmental adaptations affecting thiamine metabolism

Research Methodology for Comparative Studies:

A systematic comparison would involve:

• Side-by-side kinetic analysis of recombinant human and Macaca fascicularis SLC25A19

• Cross-species complementation studies in cellular models

• Comparative analysis of expression patterns in different tissues

• Investigation of species-specific interaction partners

Understanding these differences could provide insights into evolutionary adaptations in thiamine metabolism and inform the translation of findings between species.

What novel therapeutic approaches might target SLC25A19 dysfunction in mitochondrial disorders?

Several innovative therapeutic strategies could address SLC25A19 dysfunction:

1. Precision Medicine Approaches Based on Variant Mechanism:

2. Gene Therapy Approaches:

• AAV-mediated delivery of functional SLC25A19 to affected tissues

• CRISPR-based correction of pathogenic variants

• mRNA therapeutics for transient expression of functional protein

3. Metabolic Bypass Strategies:

• Development of cell-permeable TPP derivatives that bypass the need for SLC25A19

• Enhancement of alternative TPP transport mechanisms

• Metabolic interventions targeting downstream pathways affected by TPP deficiency

4. Mitochondrial Function Enhancers:

Evaluating Therapeutic Efficacy: To assess the effectiveness of these approaches, researchers could monitor: