Recombinant Lithobates catesbeiana CDGSH iron-sulfur domain-containing protein 2 (cisd2)

What is the basic structure of Lithobates catesbeiana CISD2 protein?

Lithobates catesbeiana CISD2 is a full-length protein consisting of 135 amino acids with a CDGSH iron-sulfur binding domain. The recombinant version features an N-terminal His-tag and has the following amino acid sequence: MVLEILARVIKVQLPAYLKRLPVPDSIAGFIRLTVSEWLRLLPFLGVLALLGYLAIRPFLPKKKQQKDSLINLKIQKENPKVVNEIDIEDLRIAKVAYCRCWRSKTFPVCDGSHNKHNELTGDNVGPLILKKKEV . The protein contains the characteristic CDGSH domain, which is part of an iron-sulfur (2Fe-2S) binding motif found in several important proteins that regulate iron and reactive oxygen metabolism .

How does the CDGSH domain function as an iron-sulfur binding motif?

The CDGSH domain in CISD2 features a consensus sequence [C-X-C-X2-(S/T)-X3-P-X-C-D-G-(S/A/T)-H], where the 3Cys-1His coordinates a 2Fe-2S iron-sulfur cluster . Initially misannotated as a zinc finger binding domain, the CDGSH domain was later confirmed to bind a 2Fe-2S cluster, which is central to its biological functions . This domain is critical for electron transfer processes and redox reactions within the protein, serving as the functional core for CISD2's roles in calcium homeostasis, iron metabolism, and mitochondrial function.

What experimental conditions affect the stability of recombinant Lithobates catesbeiana CISD2?

Recombinant CISD2 from Lithobates catesbeiana requires specific storage and handling conditions to maintain stability. The protein should be stored as a lyophilized powder at -20°C/-80°C upon receipt, with aliquoting necessary for multiple uses to avoid repeated freeze-thaw cycles . For reconstitution, the protein should be dissolved in deionized sterile water to a concentration of 0.1-1.0 mg/mL, with 5-50% glycerol (final concentration) added for long-term storage . Research indicates that temperature fluctuations, oxidative conditions, and pH changes can significantly affect the stability of the iron-sulfur cluster within the CDGSH domain, potentially compromising the protein's functional integrity.

How has the CDGSH domain evolved across species, and what does this suggest about CISD2 functions?

Phylogenetic analysis reveals that the CDGSH domain is ancient in origin, likely emerging in response to the prevalence of iron-sulfur driven metabolism in early organisms . The evolutionary pathway suggests that a CISD3-like protein with two CDGSH domains on the same polypeptide represents the ancient archetype of CDGSH proteins . CISD1/2 type proteins with a single CDGSH domain that function as homodimers emerged after the divergence of bacteria and archaea/eukaryotes from their common ancestor . This evolutionary conservation across diverse species underscores the fundamental importance of CISD2's biological functions, particularly in mitochondrial processes and redox regulation.

What are the key molecular differences between amphibian CISD2 and mammalian CISD2?

While both amphibian and mammalian CISD2 proteins contain the characteristic CDGSH domain, comparative sequence analysis reveals species-specific variations in non-catalytic regions that may influence protein-protein interactions, subcellular localization, and regulatory mechanisms. The Lithobates catesbeiana (American bullfrog) CISD2 shares core functional domains with mammalian counterparts but may exhibit unique adaptations related to the amphibian's physiology, particularly regarding metabolic regulation during metamorphosis and environmental stress responses . Research using heterologous expression systems suggests that despite these differences, amphibian CISD2 can interact with components of conserved cellular pathways, making it valuable for comparative studies of CISD2 function across vertebrate lineages.

What are the optimal expression systems for producing functional recombinant Lithobates catesbeiana CISD2?

For recombinant expression of Lithobates catesbeiana CISD2, E. coli has been established as an effective heterologous system . When expressing this protein, several critical factors must be optimized:

• Expression vector selection: Vectors with T7 or similar strong promoters combined with appropriate affinity tags (His-tag being most common) yield the best results .

• Host strain optimization: BL21(DE3) or Rosetta strains are preferred for their reduced protease activity and enhanced expression of rare codons.

• Induction conditions: IPTG concentration (typically 0.1-1.0 mM), induction temperature (16-30°C), and duration (4-24 hours) must be carefully optimized to maximize soluble protein yield.

• Buffer optimization: Inclusion of reducing agents (DTT or β-mercaptoethanol) and stabilizers during purification helps maintain the integrity of the iron-sulfur cluster in the CDGSH domain.

For applications requiring post-translational modifications not available in prokaryotic systems, insect cell or mammalian expression systems may be considered, though with potentially lower yields.

What methodological considerations are important when studying CISD2's role in mitochondrial function?

When investigating CISD2's impact on mitochondrial function, researchers should employ a multi-faceted approach:

• Subcellular fractionation techniques: Proper isolation of mitochondria while preserving CISD2-associated complexes is essential. Differential centrifugation combined with density gradient separation yields the purest mitochondrial fractions.

• Respirometry analysis: High-resolution respirometry (using Oroboros or Seahorse systems) should be conducted to assess how CISD2 affects mitochondrial respiration rates, coupling efficiency, and responses to inhibitors.

• Mitochondrial membrane potential measurements: Fluorescent probes (JC-1, TMRM) should be calibrated carefully to avoid artifacts when measuring how CISD2 impacts mitochondrial membrane potential.

• ROS detection methods: Multiple complementary approaches (DCF-DA, MitoSOX, EPR spectroscopy) should be employed to comprehensively assess how CISD2 modulates mitochondrial reactive oxygen species production.

• Calcium flux analysis: Since CISD2 influences calcium homeostasis, techniques like Rhod-2 fluorescence microscopy or calcium-selective electrodes should be utilized to monitor mitochondrial calcium handling.

These methodological considerations are particularly important when comparing wild-type CISD2 function to mutant variants or when assessing the effects of CISD2 overexpression or knockdown on mitochondrial health .

What are the technical challenges in crystallizing CISD2 for structural studies?

Crystallizing CISD2 for structural determination presents several technical challenges that researchers must address:

• Protein stability: The iron-sulfur cluster in the CDGSH domain is oxygen-sensitive and can degrade during purification and crystallization attempts. Working under anaerobic conditions or with reducing agents is essential.

• Conformational heterogeneity: CISD2 may exist in multiple conformational states, particularly when transitioning between oxidized and reduced forms of the iron-sulfur cluster, complicating crystal formation.

• Membrane association: CISD2's association with membranes necessitates careful detergent selection for extraction while maintaining native conformation. Detergent screening is critical.

• Protein-protein interactions: Native CISD2 forms homodimers and potentially interacts with other proteins, creating additional variability in crystallization attempts.

• Post-translational modifications: Variations in phosphorylation or other modifications can create microheterogeneity in the protein sample.

Successful strategies include using truncated constructs focusing on the CDGSH domain, employing fusion partners to enhance solubility, and extensive screening of crystallization conditions with varying pH, salt concentrations, and precipitants under anaerobic conditions.

How does CISD2 expression level influence cellular aging processes?

CISD2 expression levels play a crucial role in cellular aging through multiple mechanisms:

• Mitochondrial quality control: CISD2 deficiency causes an accelerated aging phenotype characterized by the accumulation of damaged mitochondria, while CISD2 overexpression provides mitochondrial protection against typical age-associated alterations .

• Redox homeostasis: CISD2 contributes to reactive oxygen species (ROS) regulation, with higher expression levels associated with enhanced antioxidant capacity . This modulation of cellular redox status significantly impacts the rate of age-related oxidative damage.

• Calcium homeostasis: CISD2 regulates Ca²⁺ buffering, preventing the calcium dysregulation commonly observed in aging cells .

• Autophagy regulation: CISD2 influences autophagic flux, which is essential for removing damaged cellular components that accumulate with age .

Experimental evidence indicates that CISD2 expression typically decreases with age in multiple tissues, correlating with increased cellular dysfunction. Notably, interventions that maintain or enhance CISD2 expression, such as exercise training regimens, appear to slow down aging processes, particularly in metabolically active tissues like the liver .

What is the experimental evidence linking CISD2 to Alzheimer's disease pathology?

Compelling experimental evidence establishes CISD2 as a significant factor in Alzheimer's disease (AD) pathology:

• Neuroprotective effects: Research demonstrates that CISD2 overexpression attenuates AD pathogenesis by maintaining mitochondrial quality and synaptic functions .

• Amyloid-beta interactions: CISD2 plays a protective role against Aβ-mediated mitochondrial damage, a central pathological process in AD . Studies show that CISD2 can mitigate the mitochondrial dysfunction caused by Aβ aggregation.

• Calcium homeostasis: CISD2's role in Ca²⁺ buffering helps prevent the calcium dysregulation associated with AD progression .

• Autophagy regulation: CISD2 influences autophagic flux, which is critical for clearing protein aggregates like those found in AD .

• Oxidative stress protection: CISD2's involvement in ROS homeostasis provides protection against the oxidative damage prominent in AD brains.

These findings suggest that therapeutic strategies aimed at enhancing CISD2 expression or activity could represent a novel approach to AD treatment, targeting multiple pathological mechanisms simultaneously .

What methodological approaches can best assess the potential anti-aging effects of CISD2 modulation?

To rigorously evaluate CISD2's anti-aging potential, researchers should implement these methodological approaches:

• Genetic manipulation models:

  • Conditional knockout and overexpression systems allow temporal control of CISD2 levels

  • CRISPR-based technologies for introducing specific CISD2 mutations

  • Tissue-specific modulation to distinguish direct from systemic effects

• Aging biomarker assessment:

  • Telomere length measurements

  • DNA methylation clocks (epigenetic aging)

  • Advanced glycation end-products quantification

  • Senescence-associated β-galactosidase activity

  • Mitochondrial DNA mutation accumulation rates

• Functional assessments across multiple systems:

  • Cognitive testing for neurological function

  • Metabolic challenge tests for metabolic flexibility

  • Exercise capacity and recovery measurements

  • Immune response to standardized challenges

• Molecular analysis techniques:

  • Multi-omics approaches (transcriptomics, proteomics, metabolomics)

  • Phosphoproteomics to map CISD2's effect on signaling networks

  • Single-cell analysis to identify cell-type specific responses

• Longitudinal studies with multiple intervention timepoints:

  • Early-life vs. mid-life vs. late-life CISD2 modulation

  • Combinatorial approaches with established anti-aging interventions

This comprehensive methodology would clarify whether CISD2 enhancement represents a viable anti-aging strategy and identify the optimal timing and tissue targets for intervention .

What is the role of CISD2 in redox homeostasis and how can this be experimentally measured?

CISD2 plays a critical role in cellular redox homeostasis through several interconnected mechanisms:

• Iron-sulfur cluster activity: The 2Fe-2S cluster within CISD2's CDGSH domain participates in electron transfer reactions, serving as a redox-active center that can buffer fluctuations in cellular redox status .

• Mitochondrial ROS regulation: CISD2 influences mitochondrial reactive oxygen species production and clearance pathways, with upregulation correlating with increased antioxidant capacity .

• Redox-sensitive protein interactions: CISD2 interacts with various proteins in a redox-dependent manner, potentially acting as a redox sensor that regulates multiple cellular pathways.

To experimentally measure CISD2's impact on redox homeostasis, researchers should employ:

• Real-time ROS detection using:

  • Genetically encoded redox-sensitive fluorescent proteins (roGFP, HyPer)

  • Small-molecule probes with different subcellular targeting (MitoSOX, CellROX)

  • Electron paramagnetic resonance (EPR) spectroscopy for direct ROS measurement

• Redox proteomics to assess:

  • Global protein thiol oxidation states

  • Glutathionylation profiles

  • Protein carbonylation levels

• Enzymatic activity assays for:

  • Superoxide dismutase

  • Catalase

  • Glutathione peroxidase/reductase systems

• Metabolic flux analysis of:

  • NADPH/NADP+ ratios

  • GSH/GSSG levels

  • Thioredoxin system activity

These approaches can quantitatively determine how CISD2 modulation affects cellular redox status under various physiological and pathological conditions .

How does CISD2 influence cancer progression at the molecular level?

CISD2 influences cancer progression through multiple interconnected molecular mechanisms:

• Cell survival and apoptosis regulation:

  • CISD2 silencing in lung adenocarcinoma cells causes a significant increase in apoptotic fraction (annexin V-high/PI-low)

  • Knockdown of CISD2 increases molecular markers of apoptosis (cytochrome c, cleaved caspase 3, and PARP1)

  • CISD2 expression appears advantageous to cancer cell proliferation/viability and survival

• Invasiveness and metastatic potential:

  • CISD2-silenced cancer cells exhibit decreased invasive capability

  • Forced expression of CISD2 results in significantly increased invasion

  • CISD2 may influence epithelial-to-mesenchymal transition (EMT), a process linked to metastasis

• Redox homeostasis and therapy resistance:

  • Upregulation of CISD2 contributes to enhanced ROS homeostasis in cancer cells

  • CISD2 may protect cancer cells from oxidative stress-induced damage

  • In the presence of the anticancer drug cisplatin, CISD2-depleted cells show increased apoptosis, suggesting CISD2 may contribute to chemoresistance

These findings suggest that CISD2 inhibition could potentially sensitize cancer cells to treatment, particularly therapies that increase ROS production or induce apoptosis through pathways affected by CISD2 .

What methodological approaches can distinguish between the direct metabolic effects of CISD2 and its secondary signaling outcomes?

To distinguish between CISD2's direct metabolic effects and secondary signaling consequences, researchers should implement this multi-faceted methodological framework:

• Temporal analysis using inducible systems:

  • Employ rapid induction systems (e.g., tetracycline-controlled or optogenetic regulation)

  • Perform time-course analyses to separate immediate effects (likely direct) from delayed responses (likely secondary)

  • Use pulse-chase experiments to track metabolic flux changes following CISD2 modulation

• Structure-function correlation studies:

  • Create point mutations that specifically disrupt iron-sulfur cluster binding

  • Generate domain-specific deletions to separate redox functions from protein-interaction domains

  • Develop conformation-specific antibodies to track CISD2 structural states

• Proximity-based interaction mapping:

  • Apply BioID or APEX2 proximity labeling to identify proteins directly interacting with CISD2

  • Implement crosslinking mass spectrometry to capture transient interactions

  • Use FRET-based sensors to monitor real-time CISD2 interactions with putative partners

• Metabolic flux analysis:

  • Employ isotope tracing (¹³C, ¹⁵N) to track CISD2-dependent changes in metabolic pathways

  • Measure oxygen consumption rate and extracellular acidification rate changes with temporal resolution

  • Analyze NAD⁺/NADH and NADP⁺/NADPH ratios as immediate indicators of redox changes

• Pharmacological perturbation strategies:

  • Use specific inhibitors of downstream signaling pathways to block secondary effects

  • Apply metabolic inhibitors to assess pathway dependencies

  • Implement parallel runs of integrated transcriptomic and metabolomic analyses to separate primary from secondary responses

This comprehensive approach allows researchers to create mechanistic maps that distinguish CISD2's direct catalytic or structural roles from its broader influence on cellular signaling networks.

What are the most promising therapeutic strategies targeting CISD2 for age-related diseases?

Based on current research findings, several promising therapeutic strategies targeting CISD2 are emerging for age-related diseases:

• Gene therapy approaches:

  • Viral vector-mediated CISD2 overexpression in tissues affected by age-related degeneration

  • CRISPR-based epigenetic activation of endogenous CISD2 expression

  • mRNA delivery systems for transient CISD2 enhancement during stress conditions

• Small molecule modulators:

  • Development of compounds that stabilize CISD2's iron-sulfur cluster

  • Identification of molecules that enhance CISD2 expression through transcription factor modulation

  • Design of allosteric activators that enhance CISD2's functional activities

• Exercise-mimetic approaches:

  • Identification of exercise-induced factors that upregulate CISD2 expression

  • Development of exercise-mimetic compounds that activate the same pathways

  • Targeted delivery systems to enhance CISD2 in specific tissues most affected by aging

• Dietary and nutritional interventions:

  • Iron-sulfur cluster precursors and stabilizing nutrients

  • Bioactive compounds that enhance CISD2 expression or activity

  • Combination approaches with other mitochondrial-targeted nutraceuticals

• Repurposing existing drugs:

  • Screening FDA-approved drugs for CISD2-modulating effects

  • Identifying approved compounds that work synergistically with CISD2 enhancement

  • Developing combination therapies targeting multiple aspects of age-related pathologies

For Alzheimer's disease specifically, CISD2 overexpression has shown particular promise in attenuating pathogenesis by maintaining mitochondrial quality and synaptic functions . These findings highlight CISD2 as a novel therapeutic target addressing multiple aspects of age-related degeneration simultaneously.

How can comparative studies between amphibian and mammalian CISD2 inform our understanding of its evolutionary adaptations?

Comparative studies between amphibian (Lithobates catesbeiana) and mammalian CISD2 can provide unique insights into evolutionary adaptations of this protein:

• Functional conservation analysis:

  • Heterologous expression studies to determine if amphibian CISD2 can rescue mammalian CISD2 deficiency

  • Binding partner comparison to identify conserved versus species-specific interactions

  • Structure-function analysis to identify differentially evolved domains outside the conserved CDGSH motif

• Environmental adaptation mechanisms:

  • Investigation of how amphibian CISD2 responds to temperature fluctuations compared to mammalian counterparts

  • Analysis of oxygen sensitivity differences, particularly relevant to amphibians' ability to withstand varying oxygen levels

  • Examination of how CISD2 functions during metamorphosis, a dramatic physiological transition unique to amphibians

• Aging and lifespan regulation:

  • Comparison of CISD2 expression patterns across lifespan in amphibians versus mammals

  • Analysis of CISD2's role in the notably different aging rates observed between some amphibian species and mammals

  • Investigation of potentially unique protective mechanisms in long-lived amphibian species

• Metabolic regulation differences:

  • Study of CISD2's role in estivation/hibernation in amphibians versus mammalian torpor

  • Analysis of CISD2 function during dramatic metabolic shifts that occur during amphibian development

  • Comparison of CISD2 involvement in ROS management during metabolic stress in both lineages

These comparative approaches can reveal which CISD2 functions represent core ancient mechanisms versus those that evolved as adaptive specializations, potentially identifying new therapeutic targets or approaches for age-related diseases .

What novel techniques could advance our understanding of CISD2's dynamics and interactions in living systems?

Several cutting-edge techniques hold promise for advancing our understanding of CISD2 dynamics and interactions in living systems:

• Advanced imaging technologies:

  • Super-resolution microscopy (PALM/STORM) to visualize CISD2 distribution at nanoscale resolution

  • Cryo-electron tomography to observe CISD2 in native cellular environments

  • Label-free imaging techniques (CARS, SRS) to track CISD2 without potentially disruptive tags

• Real-time monitoring tools:

  • Genetically encoded biosensors for tracking CISD2 conformational changes

  • FRET-based reporters to monitor CISD2 interactions with partners in real-time

  • Iron-sulfur cluster-specific probes to assess CISD2 redox state fluctuations

• In situ structural techniques:

  • In-cell NMR to determine CISD2 structure in living cells

  • Hydrogen-deuterium exchange mass spectrometry to map dynamic protein interactions

  • Single-molecule tracking to follow individual CISD2 proteins through cellular compartments

• Systems biology approaches:

  • Multi-omics integration (transcriptomics, proteomics, metabolomics) to build comprehensive CISD2 interaction networks

  • Machine learning algorithms to predict condition-specific CISD2 functions from large datasets

  • Network perturbation analysis to identify critical nodes in CISD2-dependent pathways

• Advanced genetic tools:

  • Spatiotemporally controlled genome editing to modulate CISD2 with unprecedented precision

  • Synthetic genetic circuits to test CISD2 function in defined contexts

  • Humanized animal models expressing species-specific CISD2 variants

These innovative approaches will provide deeper insights into CISD2's dynamic behavior under physiological and pathological conditions, potentially revealing new therapeutic opportunities for age-related diseases and cancer.