Recombinant Xenopus tropicalis Helicase ARIP4 (rad54l2), partial
Description
2.1. TOP2-Linked DNA Damage Avoidance
RAD54L2 mediates a conserved pathway to prevent TOP2 cleavage complex (TOP2cc) accumulation, which causes genomic instability. Key findings:
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Mechanism: Promotes TOP2 turnover from chromatin via proteasome-dependent and -independent pathways, reducing trapped TOP2ccs .
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Synergy with TDP2: RAD54L2 deficiency enhances sensitivity to TOP2 poisons (e.g., etoposide), particularly in TDP2-knockout cells .
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Clinical Relevance: Impaired RAD54L2 function correlates with poor outcomes in cancers treated with TOP2 inhibitors .
2.2. R-Loop Resolution and Transcription
RAD54L2 facilitates androgen receptor-driven transcription by resolving R-loops at promoter regions:
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Catalytic Requirement: Helicase activity (ATPase-dependent) is critical for Pol II progression and nascent RNA synthesis .
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Chromatin Localization: Enriched at transcription start sites (TSS) of AR target genes, preventing R-loop accumulation .
3.1. Crossover Suppression
RAD54L2 collaborates with BLM helicase to regulate recombination outcomes:
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SCE Reduction: RAD54L2 knockout increases sister chromatid exchanges (SCEs), mimicking BLM deficiency phenotypes .
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Non-Crossover Promotion: Works in the BLM-TOP3A-RMI1/2 pathway to favor error-free repair (Fig. 1).
3.2. Anaphase Bridge Prevention
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Ultrafine Bridge Suppression: RAD54L2 deficiency elevates ultrafine anaphase bridges (29% vs. 43% in BLM knockdowns), indicating unresolved recombination intermediates .
Experimental Applications
This recombinant protein is utilized to:
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Study Helicase Mechanisms: Assess ATPase activity, DNA unwinding, and chromatin remodeling in vitro .
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Investigate TOP2 Poison Resistance: Screen for modifiers of etoposide sensitivity in genetic models .
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Develop Therapeutic Strategies: Identify RAD54L2 inhibitors to potentiate TOP2-targeted chemotherapy .
Comparative Analysis with Orthologs
The Xenopus tropicalis variant shares >80% sequence homology with human RAD54L2 but differs in:
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Post-Translational Modifications: Xenopus lacks certain SUMOylation sites critical for human ZATT/ZNF451 interactions .
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Expression Systems: Mammalian cell-produced Xenopus RAD54L2 achieves higher solubility than E. coli variants .
Limitations and Future Directions
Product Specs
Target Background
Q&A
What is the biological role of Helicase ARIP4 (RAD54L2) in Xenopus tropicalis?
Helicase ARIP4 (RAD54L2) is an SNF2-family ATP-dependent chromatin remodeler critical for resolving transcription-associated R-loops and facilitating androgen receptor (AR)-mediated transcriptional activation . In Xenopus tropicalis, it serves as a model system to study conserved mechanisms of DNA repair and hormone signaling due to its diploid genome and experimental tractability . Key roles include:
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R-loop resolution: ARIP4 resolves DNA-RNA hybrids at transcription start sites (TSSs), preventing transcriptional stalling and genome instability .
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Androgen signaling: It interacts with topoisomerase IIβ (TOP2β) to mediate transient DNA double-strand breaks (DSBs) required for AR-dependent gene activation .
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Chromatin remodeling: ARIP4 hydrolyzes ATP to reposition nucleosomes, enabling Pol II progression at paused promoters .
Methodological Insight: To validate these roles, researchers use chromatin immunoprecipitation sequencing (ChIP-seq) to map ARIP4 occupancy at TSSs , in vitro ATPase assays to quantify catalytic activity , and transient transfection of helicase-dead mutants (e.g., DE462/463AA) to dissect structure-function relationships .
How should researchers design experiments to study recombinant ARIP4 in vitro?
Recombinant ARIP4 (partial, Ala638–Ser837) is typically expressed in E. coli with an N-terminal His-tag for purification . Key experimental considerations:
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Activity assays: Measure ATP hydrolysis rates using malachite green assays under varying DNA substrates (e.g., dsDNA, R-loops) .
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Substrate specificity: Use electrophoretic mobility shift assays (EMSAs) to test binding to G-quadruplexes or androgen response elements (AREs) .
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Functional reconstitution: Combine ARIP4 with TOP2β and PARP1 in chromatinized templates to model transcriptional activation .
Data Table 1: In Vitro Functional Assays for Recombinant ARIP4
| Assay Type | Substrate | Key Finding | Source |
|---|---|---|---|
| ATPase Activity | dsDNA | ||
| DNA Binding (EMSA) | G-quadruplex | ||
| R-loop Resolution | DNA-RNA hybrid | 80% resolution efficiency in 30 min |
How can discrepancies between in vitro and in vivo ARIP4 activity be reconciled?
Discrepancies often arise from:
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Cofactor requirements: In vitro systems may lack TOP2β or PARP1, which are essential for DSB formation in vivo .
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Chromatin context: Recombinant ARIP4 assays using naked DNA neglect nucleosome positioning effects .
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Post-translational modifications: Phosphorylation at Ser837 (predicted in X. tropicalis) modulates helicase activity but is absent in bacterial expression systems .
Methodological Resolution:
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Use Xenopus egg extract systems to study ARIP4 in chromatinized templates .
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Perform mass spectrometry to identify post-translational modifications in endogenous ARIP4 .
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Combine CRISPR-Cas9 knockout in X. tropicalis with rescue assays using wild-type/mutant ARIP4 .
What genetic redundancies complicate ARIP4 functional studies in Xenopus tropicalis?
X. tropicalis has two RAD54L paralogs (RAD54L1/L2), but ARIP4 (RAD54L2) shows unique roles in androgen signaling . Redundancy challenges include:
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Compensatory mechanisms: RAD54L1 may partially rescue ARIP4 knockout phenotypes.
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Diploid limitations: Unlike tetraploid X. laevis, X. tropicalis lacks buffering from homologous chromosomes .
Data Table 2: Genetic Tools for ARIP4 Studies in Xenopus
How do ARIP4 interactions with TOP2β and PARP1 influence transcriptional outcomes?
ARIP4 forms a complex with TOP2β and PARP1 to coordinate DSB formation and repair during AR activation :
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TOP2β interaction: Generates transient DSBs at TSSs to relieve torsional stress during Pol II elongation .
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PARP1 recruitment: Facilitates chromatin decompaction through poly-ADP ribosylation .
Methodological Insight:
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Co-immunoprecipitation (Co-IP) in LNCaP cells confirms ARIP4-TOP2β-PARP1 complex formation .
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Inhibiting TOP2β (with etoposide) or PARP1 (with olaparib) abrogates ARIP4-dependent transcription .
What controls are essential when using recombinant ARIP4 in helicase assays?
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Negative controls: Helicase-dead mutants (K310A) and ATP-depleted reactions .
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Substrate specificity: Include non-cognate DNA (e.g., ssDNA) to rule out nonspecific activity .
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Buffer optimization: Test Mg²⁺ (1–10 mM) and KCl (50–150 mM) concentrations to match physiological conditions .
