Recombinant Human ADP/ATP translocase 4 (SLC25A31)

What is the function of SLC25A31 and how does it differ from other mitochondrial carriers?

SLC25A31 encodes ADP/ATP translocase 4, a critical mitochondrial membrane protein that catalyzes the exchange of cytoplasmic ADP with mitochondrial ATP across the inner membrane . While functionally similar to other ADP/ATP translocases, SLC25A31 has a specialized role in the distal flagellum, serving as a nucleotide shuttle between flagellar glycolysis, protein phosphorylation, and motility mechanisms .

For studying functional differences between SLC25A31 and other family members:

• Transport assay methodology: Reconstitute purified recombinant SLC25A31 in liposomes loaded with ATP, then measure ADP uptake rates compared to other ANT isoforms using radiolabeled substrates.

• Tissue expression profiling: Unlike the more ubiquitous ANT isoforms, SLC25A31 shows restricted expression in brain, liver, sperm, and testis tissue, requiring tissue-specific experimental designs .

• Substrate specificity analysis: While all ANTs transport ADP and ATP, subtle differences in transport kinetics can be evaluated using competitive inhibition assays with ADP/ATP analogs.

Research shows SLC25A31 belongs to the Mitochondrial carrier (TC 2.A.29) protein family and represents the fourth member of the adenine nucleotide translocases, with distinct evolutionary conservation patterns across species including human, mouse, rat, bovine, and chimpanzee .

What tissue expression patterns characterize SLC25A31 and what methodologies best detect its presence?

SLC25A31 exhibits a highly specific expression pattern, predominantly found in the brain, liver, sperm, and testis . This restricted distribution suggests tissue-specific functions that differentiate it from more ubiquitously expressed ADP/ATP translocases.

Recommended detection methodologies:

When designing experiments to detect SLC25A31:

• Include positive controls from testis tissue where expression is highest

• Incorporate negative controls from tissues lacking expression

• Validate antibody specificity using recombinant protein standards

• Consider potential cross-reactivity with other ANT family members

The canonical human SLC25A31 protein has 315 amino acid residues with a molecular mass of 35 kDa, which serves as a reference for proper identification in experimental procedures .

What are the optimal systems for producing recombinant SLC25A31 protein for research applications?

Several expression systems have been validated for producing functional recombinant SLC25A31 protein, each with distinct advantages depending on research goals:

When producing recombinant SLC25A31:

• For basic structural characterization, E. coli-expressed protein is sufficient and commercially available as "Recombinant Human ADP/ATP translocase 4 (SLC25A31)" from several suppliers .

• For transport assays, consider using baculovirus or mammalian expression systems to maintain proper folding and membrane insertion.

• Include purification tags that can be removed without affecting protein function.

• Verify protein activity through ADP/ATP exchange assays before proceeding with experiments.

Several vendors offer recombinant SLC25A31 preparations in various host systems, enabling researchers to select the most appropriate form for their specific experimental needs .

How can genetic interaction studies enhance our understanding of SLC25A31 function?

Recent CRISPR-based screens have revealed important insights about SLC25A31's genetic interactions and metabolic context-dependent functions. A systematic approach to studying genetic interactions includes:

• Dual Cas9 system methodology: Utilize different PAM sequences recognized by SpCas9 and SaCas9 to simultaneously knock out SLC25A31 and potential interacting genes .

• Media condition variations: Test genetic interactions under multiple metabolic states (glucose, galactose, antimycin) to uncover context-dependent functions .

• Interaction classification framework:

  • GxE (Gene x Environment) interactions: How SLC25A31 KO affects fitness under specific metabolic conditions

  • GxG (Gene x Gene) interactions: How SLC25A31 KO combined with other gene KOs produces non-additive phenotypes

  • GxGxE (Gene x Gene x Environment) interactions: How genetic interactions change across metabolic environments

Research has shown that SLC25A31 is minimally expressed in certain cell types, serving as a negative control in CRISPR screens designed to identify redundant functions among mitochondrial carriers . This suggests researchers should carefully validate SLC25A31 expression in their specific experimental systems before attributing phenotypes to its function.

The selection of appropriate controls is critical when designing genetic interaction experiments involving SLC25A31:

• Positive controls: Use known synthetic lethal pairs (e.g., BCL2L1 + MCL1)

• Negative controls: Include non-expressed genes in the cell type of interest

• Cutting controls: Incorporate guides targeting non-essential loci to account for DNA damage effects

What methodological approaches can detect SLC25A31's role in mitochondrial disease pathogenesis?

SLC25A31 has been implicated in secondary mitochondrial diseases (SMDs), which arise from mutations in nuclear-encoded genes that influence oxidative phosphorylation assembly and operation . Researchers investigating these connections should consider:

• Patient cohort selection strategy: Focus on individuals with clinical presentations of mitochondrial dysfunction in tissues where SLC25A31 is predominantly expressed (brain, testis).

• Sequencing approach optimization:

  • Targeted sequencing of SLC25A31 and related mitochondrial carriers

  • Whole-exome sequencing to identify variants in SLC25A31 and interacting partners

  • RNA-seq to evaluate expression changes in patient tissues

• Functional validation protocol sequence:

  • Measure ATP/ADP exchange rates in patient-derived fibroblasts

  • Assess mitochondrial membrane potential using potentiometric dyes

  • Evaluate respiratory capacity through oxygen consumption measurements

  • Perform metabolic flux analysis to quantify metabolic pathway alterations

• Disease model development:

  • Generate patient-specific iPSCs with SLC25A31 mutations

  • Differentiate into relevant cell types (neurons, spermatocytes)

  • Create isogenic controls using CRISPR-Cas9 correction

SLC25A31 has been specifically linked to microcephaly in the literature, suggesting its role in brain development may involve critical energy provision mechanisms during neurogenesis . This association provides a framework for investigating how nucleotide transport defects may contribute to neurodevelopmental disorders.

What strategies can researchers employ to study SLC25A31's role in flagellar function and sperm motility?

SLC25A31's enrichment in sperm and potential role in flagellar energy metabolism makes it an important target for reproductive biology research. A comprehensive investigation would include:

• Subcellular localization optimization:

  • Immunofluorescence with confocal microscopy to precisely map SLC25A31 distribution within sperm flagellum

  • Super-resolution microscopy to determine proximity to other energy-producing enzymes

  • Immuno-electron microscopy to visualize association with specific flagellar structures

• Functional sperm analysis methodology:

  • Computer-assisted sperm analysis (CASA) before and after SLC25A31 inhibition

  • Measurement of local ATP concentrations using luciferase-based reporters

  • Microfluorimetric analysis of flagellar calcium dynamics during motility

• ATP/ADP shuttle mechanism investigation:

  • Develop a model system to test SLC25A31's role as "a nucleotide shuttle between flagellar glycolysis, protein phosphorylation and mechanisms of motility"

  • Use metabolic labeling to track ATP movement within different flagellar compartments

  • Correlate SLC25A31 activity with flagellar bend amplitude and beat frequency

• Animal model approach:

  • Generate sperm-specific SLC25A31 knockout mice

  • Evaluate fertility parameters and detailed sperm function metrics

  • Perform rescue experiments with wild-type SLC25A31 to confirm specificity

Since SLC25A31 may "serve to mediate energy generating and energy consuming processes in the distal flagellum" , researchers should design experiments that can distinguish local ATP production from mitochondrial-derived ATP transport.

Which antibodies are most reliable for SLC25A31 detection in different experimental applications?

Selecting the appropriate antibody is critical for SLC25A31 research. Based on validated products:

When selecting antibodies for SLC25A31 research:

• Application-specific considerations:

  • For Western blot: Select antibodies targeting conserved epitopes for highest sensitivity

  • For IHC/IF: Choose antibodies validated specifically for morphological applications

  • For proximity ligation assays: Select antibodies raised in different host species

• Validation methodology:

  • Confirm specificity using SLC25A31 knockout/knockdown controls

  • Test for cross-reactivity with other ANT family members

  • Verify detection in tissues with known expression (testis) versus negative control tissues

• Technical optimizations:

  • For mitochondrial proteins, optimize permeabilization conditions

  • Consider native versus denaturing conditions based on epitope accessibility

  • Validate lot-to-lot consistency with standard positive controls

Western Blot remains the most widely used application for SLC25A31 antibodies, while ELISA, Immunofluorescence, and Immunohistochemistry are also common approaches for different research questions .

How can CRISPR-Cas9 technology be optimized for investigating SLC25A31 function?

CRISPR-Cas9 technology offers powerful approaches for studying SLC25A31 with several strategic considerations:

• Guide RNA design strategy:

  • Target conserved functional domains for complete loss-of-function

  • Design guides with minimal off-target effects using established algorithms

  • Consider PAM site availability in highly conserved regions

  • For dual knockout studies, select compatible Cas9 variants (SpCas9 and SaCas9) that recognize different PAM sequences

• Experimental design framework:

  • Generate complete knockout cell lines to study core functions

  • Create domain-specific mutations to dissect structure-function relationships

  • Develop inducible knockdown systems for temporal control

  • Employ homology-directed repair to introduce tagged versions for localization studies

• Phenotypic analysis methodology:

  • Assess mitochondrial membrane potential changes

  • Measure cellular respiration rates in modified media conditions

  • Quantify ATP/ADP ratios in different cellular compartments

  • Evaluate metabolic adaptations through metabolomics

  • Screen for synthetic interactions using dual-guide libraries

• Validation controls:

  • Include non-cutting controls to account for Cas9 toxicity

  • Use guide RNAs targeting olfactory receptors or other non-essential genes as negative controls

  • Perform rescue experiments with wild-type SLC25A31 to confirm specificity

Recent CRISPR screening approaches have utilized SLC25A31 as a negative control in certain cell types where it's not expressed, which provides methodological guidance for properly controlled experiments .

What metabolic condition variations should be incorporated when studying SLC25A31 function?

Understanding how different metabolic states affect SLC25A31 function is crucial for comprehensive characterization:

• Media condition experimental design:

  • Glucose media: Represents glycolysis-dominant metabolism

  • Galactose media: Forces cells to rely on OXPHOS

  • Glutamine-only media: Tests mitochondrial glutamine metabolism

  • Antimycin treatment: Inhibits complex III to block OXPHOS

• Analytical approach for metabolic adaptations:

  • Measure cellular growth rates in each condition

  • Quantify mitochondrial and cytosolic ATP/ADP ratios

  • Monitor membrane potential changes during metabolic shifts

  • Analyze metabolic flux using stable isotope labeling

• Genetic interaction evaluation framework:

  • Test SLC25A31 knockouts alone and in combination with other genes across different media conditions

  • Classify interactions as GxE, GxG, or GxGxE based on phenotypic outcomes

  • Calculate π-scores to quantify the strength of genetic interactions

• Redundancy testing methodology:

  • Since SLC25A31 may have redundant functions with other ANT family members, test double knockouts under different metabolic conditions

  • Pay particular attention to conditions that force cells to rely on OXPHOS, where ANT function becomes critical

Research has shown that genetic interactions involving mitochondrial carriers can be strongly influenced by metabolic context, with some synthetic sick interactions only apparent under specific conditions like galactose media that force respiratory metabolism .

How should researchers interpret contradictory data regarding SLC25A31 expression patterns?

Researchers frequently encounter conflicting data about SLC25A31 expression, necessitating robust methodological approaches:

• Comprehensive validation workflow:

  • Verify antibody specificity using recombinant SLC25A31 and knockout controls

  • Apply multiple detection methods (qPCR, Western blot, immunostaining)

  • Quantify absolute expression levels using calibrated standards

  • Consider developmental timing and cellular differentiation state

• Cell line selection strategy:

  • Recognize that SLC25A31 expression is highly tissue-specific, concentrated in brain, liver, sperm, and testis

  • Understand that SLC25A31 may be absent in common laboratory cell lines, explaining its use as a negative control in some CRISPR screens

  • Include appropriate positive controls (testis tissue or cell lines) in all experiments

• Isoform detection methodology:

  • Design primers/antibodies that can distinguish SLC25A31 from other ANT family members

  • Use RNA-seq to identify possible alternative splice variants

  • Consider potential post-translational modifications that may affect detection

• Technical considerations:

  • For mitochondrial proteins, ensure proper sample preparation preserves mitochondrial integrity

  • Consider subcellular fractionation to enrich for mitochondrial proteins

  • Account for potential differences between mRNA and protein expression levels

When confronted with contradictory data, researchers should systematically evaluate the technical and biological factors that might explain the discrepancies, including differences in detection methods, experimental conditions, and the specific cellular context being studied.