Recombinant Saccharomyces cerevisiae Iron-sulfur clusters transporter ATM1, mitochondrial (ATM1)

What is the evolutionary significance of ATM1 across different species?

ATM1 represents a highly conserved family of ABC transporters present in virtually all eukaryotes. The ATM1 homolog (ScAtm1) in Saccharomyces cerevisiae is functionally similar to ABCB7 in humans, with both playing critical roles in Fe-S cluster export from mitochondria . Homologs have been identified across diverse species, including apicomplexan parasites like Plasmodium falciparum (PfATM1) and Toxoplasma gondii (TgATM1) . This conservation underscores the fundamental importance of this transporter in cellular metabolism across evolutionary boundaries.

Experimental approaches to study evolutionary conservation include:

• Complementation assays (e.g., successful complementation of TgATM1 mutants with ScATM1)

• Sequence homology analysis across species

• Functional characterization of ATM1 homologs in different organisms

What cellular processes are impaired when ATM1 is knocked out or downregulated?

Disruption of ATM1 leads to several significant cellular defects:

Methodologically, researchers typically employ conditional knockout systems, RNA interference, or CRISPR-Cas9 approaches to study ATM1 deficiency, as complete deletion is often lethal in many organisms . Phenotypic analyses include biochemical assays for Fe-S enzyme activities, iron quantification using spectroscopic methods, and transcriptional profiling.

What is the molecular structure of ATM1 and how does it influence function?

Recent cryo-electron microscopy studies of the Chaetomium thermophilum ATM1 homolog (CtAtm1) have revealed crucial structural insights at resolutions of 2.8-3.2 Å . The transporter consists of:

• Two transmembrane domains spanning the mitochondrial inner membrane

• Two nucleotide-binding domains facing the mitochondrial matrix

• A substrate-binding cavity with positive charge distribution

The structure reveals a partial occlusion state that links cargo binding to residues at the mitochondrial matrix interface. This architecture allows ATM1 to accept glutathione-complexed iron-sulfur clusters and transport them across the membrane . Structural analysis methods include:

• Cryo-electron microscopy

• Molecular docking simulations

• Structure-guided mutagenesis to validate functional residues

How do researchers differentiate between the mitochondrial transporter ATM1 and the DNA damage response protein Tel1 in experimental systems?

This question addresses a common source of confusion in yeast research. Despite similar abbreviations, ATM1 (iron-sulfur cluster transporter) and Tel1 (an ATM-related protein involved in DNA damage response) have distinct functions and cellular localizations:

Methodologically, researchers distinguish between these proteins through:

• Subcellular fractionation followed by Western blotting

• Fluorescence microscopy with tagged proteins

• Functional assays: Fe-S enzyme activities (ATM1) vs. DNA damage response (Tel1)

• Genetic complementation experiments

The study of Tel1 in S. cerevisiae has shown it plays a role in checkpoint responses to phleomycin treatment in S phase, working alongside Mec1 . When studying phenotypes related to DNA damage, researchers must be careful not to confuse Tel1-dependent phenotypes with those related to ATM1 dysfunction.

What methodologies are most effective for purifying functional recombinant ATM1 for biochemical studies?

Obtaining pure, functional recombinant ATM1 presents significant challenges due to its membrane-embedded nature. Researchers have developed several approaches:

• Expression systems:

  • E. coli: Challenge due to toxicity and inclusion body formation

  • S. cerevisiae: Native environment but lower yields

  • Insect cells (Sf9, High Five): Higher yields with proper folding

  • Mammalian cells: Most native-like post-translational modifications

• Purification strategies:

  • Detergent solubilization (commonly DDM, LMNG, or GDN)

  • Affinity chromatography using poly-histidine or other fusion tags

  • Size exclusion chromatography for final polishing

  • Reconstitution into nanodiscs or liposomes for functional studies

• Activity verification methods:

  • ATPase assays measuring ATP hydrolysis (stimulated by oxidized glutathione and [4Fe-4S])

  • Transport assays using fluorescent or radioactive substrates

  • Binding assays with putative substrates (e.g., glutathione-complexed [Fe-S] clusters)

In recent studies, P. falciparum ATM1 (PfATM1) was successfully expressed and purified, demonstrating ATP hydrolysis activity that was stimulated by oxidized glutathione (GSSG) and [4Fe-4S] clusters . This confirms ATM1 as a functional ABC transporter capable of substrate-stimulated ATPase activity.

How does ATM1 interact with other components of the iron-sulfur cluster biogenesis machinery?

ATM1 functions as a critical link between mitochondrial Fe-S cluster assembly and cytosolic Fe-S protein maturation. Research has revealed several key interactions:

Methodologically, researchers investigate these interactions through:

• Genetic epistasis analysis

• Protein-protein interaction studies (yeast two-hybrid, co-immunoprecipitation)

• In vitro reconstitution of Fe-S transfer

• Structural studies of protein complexes

In P. falciparum, PfATM1 has been shown to receive [4Fe-4S] clusters from mitochondrial ISC scaffold proteins and interact with the cytosolic CIA protein PfNBP35 . This provides evidence for ATM1's role as a bridge in the Fe-S cluster transfer pathway from mitochondria to cytosolic proteins.

What explains the contradictory findings regarding ATM1 essentiality in different Plasmodium species?

Several methodological approaches can help resolve such contradictions:

• Technical differences in gene deletion strategies:

  • Conditional vs. constitutive knockout approaches

  • Different gene editing efficiencies

  • Compensatory mutations in successful knockout lines

• Genetic background variations:

  • Strain-specific differences in metabolic requirements

  • Presence of genetic modifiers in different laboratory strains

• Environmental conditions:

  • In vitro vs. in vivo growth conditions

  • Media composition differences

  • Oxygen tension variations

• Functional redundancy assessment:

  • Investigation of paralog expression and compensation

  • Comparative transcriptomics of wild-type vs. mutant lines

  • Metabolic profiling to identify alternative pathways

To resolve such contradictions, researchers should employ standardized methodologies across laboratories, including detailed reporting of experimental conditions, strain information, and comprehensive phenotypic characterization of mutant lines.

How does ATM1 transport mechanism differ from other mitochondrial ABC transporters?

ATM1 possesses distinct structural and functional features compared to other mitochondrial ABC transporters:

• Substrate specificity:
  ATM1 preferentially transports glutathione-complexed iron-sulfur clusters, with its activity stimulated by oxidized glutathione (GSSG) . This contrasts with other mitochondrial ABC transporters that transport different substrates like peptides or metabolites.

• Transport directionality:
  ATM1 exports substrates from the mitochondrial matrix to the intermembrane space, while some other transporters function in the opposite direction or bidirectionally.

• Structural adaptations:
  The substrate-binding cavity of ATM1 contains positively charged residues that form a partially occluded state linking cargo binding to residues at the mitochondrial matrix interface . This specific architecture facilitates recognition of negatively charged glutathione-Fe-S complexes.

• ATP utilization efficiency:
  Biochemical studies of PfATM1 demonstrate ATP hydrolysis activity specifically stimulated by physiological substrates (GSSG and [4Fe-4S]) , suggesting a tightly coupled transport mechanism.

Methodologically, these differences are studied through:

• Comparative structural analysis

• Substrate specificity assays

• Site-directed mutagenesis of key residues

• Transport kinetics measurements in reconstituted systems

Understanding these molecular differences provides insights into the specialized function of ATM1 in cellular iron-sulfur metabolism and may guide development of specific modulators for research applications.

What are the most reliable reporter systems to monitor ATM1 activity in vivo?

Monitoring ATM1 activity in living cells presents challenges due to the intracellular nature of its substrates. Several effective approaches have been developed:

• Cytosolic Fe-S protein activity assays:

  • Measurement of cytosolic Fe-S enzymes (e.g., isopropylmalate isomerase, Leu1)

  • Aconitase activity assays

  • Xanthine oxidase activity

• Iron homeostasis indicators:

  • Mitochondrial iron content quantification

  • Iron-responsive element (IRE) reporter systems

  • Transcriptional profiling of iron-responsive genes

• Fluorescent substrate analogs:

  • Development of fluorescent glutathione derivatives

  • FRET-based sensors for conformational changes

• Genetic reporter systems:

  • Linking ATM1 function to expression of fluorescent proteins via Fe-S-dependent transcription factors

  • Growth-based selection systems in complementation assays

These approaches provide complementary information, with enzyme activity assays being most directly related to ATM1 function, while iron content measurements offer insights into the consequences of ATM1 dysfunction.

How can researchers reconcile the dual roles of ATM and ATM1 signaling in experimental systems?

The potential confusion between ATM1 (the mitochondrial Fe-S transporter) and ATM (Ataxia Telangiectasia Mutated, a DNA damage response kinase) requires careful experimental design:

In experimental designs, researchers should:

• Clearly define which protein is being studied

• Use specific readouts that distinguish between the two pathways

• Include appropriate controls (e.g., ATM inhibitors will not affect ATM1 function)

• Consider the context of the experiment (DNA damage vs. mitochondrial function)

In the context of Saccharomyces cerevisiae, Tel1 (not ATM1) is the homolog of mammalian ATM, functioning in DNA damage checkpoint responses particularly after phleomycin treatment in S phase . This distinction is crucial for proper experimental interpretation.

What computational approaches are most effective for predicting ATM1 substrate recognition and transport kinetics?

Computational biology offers powerful tools for understanding ATM1 function:

• Molecular docking and virtual screening:

  • Prediction of glutathione-Fe-S cluster binding modes

  • Identification of key interaction residues

  • Screening of potential modulators

• Molecular dynamics simulations:

  • Analysis of conformational changes during transport cycle

  • Investigation of water and ion movements

  • Energetics of substrate translocation

• Quantum mechanical/molecular mechanical (QM/MM) methods:

  • Electronic structure calculations for Fe-S clusters

  • Understanding the role of redox states in transport

• Machine learning approaches:

  • Prediction of transport efficiency based on substrate properties

  • Classification of potential substrates from chemical libraries

These computational approaches should be validated through experimental testing, such as site-directed mutagenesis of predicted key residues and transport assays with modified substrates.

How do mutations in human ABCB7 (ATM1 homolog) contribute to X-linked sideroblastic anemia with ataxia?

X-linked sideroblastic anemia with ataxia (XLSA/A) is a rare disorder caused by mutations in ABCB7, the human homolog of yeast ATM1. Understanding the molecular basis through yeast models provides valuable insights:

• Genotype-phenotype correlations:

  • Missense mutations in ABCB7 lead to partial function

  • Complete loss of function likely lethal (as in yeast)

  • Specific mutations affect ATPase activity or substrate binding

• Disease mechanisms:

  • Impaired cytosolic Fe-S protein maturation

  • Mitochondrial iron overload

  • Defective heme biosynthesis

  • Compromised DNA repair (due to defective Fe-S cluster assembly in DNA repair enzymes)

• Yeast models for human disease:

  • Expression of human ABCB7 variants in ATM1-deficient yeast

  • Functional complementation assays

  • Structure-function analysis of disease-associated mutations

This research direction connects fundamental studies in yeast to human disease mechanisms, providing potential therapeutic targets for XLSA/A.

How can ATM1 inhibition be exploited as a potential target in apicomplexan parasites?

The essentiality of ATM1 in certain apicomplexan parasites presents a therapeutic opportunity:

• Target validation approaches:

  • Conditional knockdown systems to confirm essentiality

  • Phenotypic analysis of ATM1-depleted parasites

  • Genetic complementation with drug-resistant variants

• High-throughput screening strategies:

  • ATPase activity inhibition assays

  • Growth inhibition assays in ATM1-downregulated parasites

  • Counterscreening against human ABCB7 for selectivity

• Structure-based drug design:

  • Exploitation of structural differences between parasite and human ATM1

  • Virtual screening for binding site inhibitors

  • Fragment-based approaches targeting allosteric sites

• Resistance mechanisms:

  • Poly(Asn) repeats in PfATM1 associated with differential drug susceptibility

  • Monitoring of resistance development in laboratory strains

  • Cross-resistance analysis with existing antimalarials

This research area represents a promising approach for developing new antiparasitic agents with novel mechanisms of action.

What technological advances would enable real-time monitoring of ATM1 transport activity in living cells?

Current limitations in visualizing ATM1 activity could be overcome through:

• Advanced imaging approaches:

  • Development of fluorescent Fe-S cluster analogs

  • FRET-based sensors for ATM1 conformational changes

  • Super-resolution microscopy of labeled ATM1 and substrates

• Biosensor development:

  • Genetically encoded sensors for cytosolic Fe-S cluster availability

  • Redox-sensitive fluorescent proteins

  • Split fluorescent protein systems linked to Fe-S protein maturation

• Single-molecule techniques:

  • Optical tweezers to measure forces during transport

  • Single-molecule FRET to monitor conformational dynamics

  • High-speed AFM to visualize structural changes

• Microfluidic approaches:

  • Real-time monitoring of cellular responses to ATM1 modulation

  • Single-cell analysis of Fe-S protein activities

  • Controlled gradients of iron availability

These technological advances would significantly enhance our understanding of ATM1 function in its native cellular environment.

How might synthetic biology approaches expand our understanding of ATM1 function?

Synthetic biology offers innovative strategies for ATM1 research:

• Minimal systems reconstitution:

  • Bottom-up assembly of Fe-S cluster export machinery

  • Artificial membrane systems with purified components

  • Coupling to synthetic Fe-S protein maturation pathways

• Protein engineering:

  • Creation of ATM1 variants with altered substrate specificity

  • Development of split-ATM1 systems for regulated activity

  • Fusion to orthogonal signaling domains for controlled activation

• Synthetic genetic circuits:

  • Engineering feedback loops to regulate ATM1 expression

  • Creating genetic switches responsive to Fe-S cluster levels

  • Computational modeling of synthetic circuits integrated with ATM1 function

• Cross-species hybrid systems:

  • Chimeric transporters combining domains from different species

  • Heterologous expression in optimized chassis organisms

  • Evolution-guided optimization of transport efficiency

These approaches would not only deepen our understanding of ATM1 function but could potentially lead to biotechnological applications leveraging its transport capabilities.