236: XPD translocation and genetic disease etiology

Paul T et al., Nat Commun - Computational modeling reveals how ATP-driven conformational cycles of the XPD helicase drive directional 5′→3′ translocation on single-stranded DNA and how mutations disrupt this process to cause disease. Key terms: XPD, DinG, ssDNA translocation, nucleotide excision repair, disease mutations.

Study Highlights:
The authors combined molecular dynamics, partial nudged elastic band path optimization, transition path sampling, and Markov state modeling to map seven metastable on-path states that define XPD’s ATPase cycle. ATP binding and hydrolysis drive reciprocal rotations of the RecA2 and Arch domains, transmitted via a spring helix and spindle helix, that alternate DNA affinity at two defined constrictions at the 5′ and 3′ ends of the DNA-binding groove. Translocation proceeds in two phases: RecA2-driven sliding of ssDNA through Constriction 1 followed by ATP hydrolysis, constriction switching and sliding through Constriction 2, advancing one nucleotide per ATP. Mapping of missense mutations shows clustering of disease-associated residues at DNA- and ATP-binding sites and classifies mutations that impair DNA binding, ATPase function, or allosteric domain dynamics

Conclusion:
A detailed mechanistic map links XPD’s nucleotide-dependent conformational switching to directional ssDNA translocation and explains how perturbations of key residues underlie XP, CS, and TTD phenotypes

Music:
Enjoy the music based on this article at the end of the episode.

Article title:
Translocation mechanism of xeroderma pigmentosum group D protein on single-stranded DNA and genetic disease etiology

First author:
Paul T

Journal:
Nat Commun

DOI:
10.1038/s41467-025-66834-1

Reference:
Paul T, Yan C, Derdeyn-Blackwell G, Ivanov I. Translocation mechanism of xeroderma pigmentosum group D protein on single-stranded DNA and genetic disease etiology. Nat Commun. 2025. https://doi.org/10.1038/s41467-025-66834-1

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2025-12-22.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music
- transcript coverage: Audited transcript portions describing XPD’s translocation mechanism, the seven-state ATPase cycle (S1–S7), the roles of Constriction 1 and Constriction 2, mutation class mapping to XP/CS/TTD phenotypes, XPD–DinG comparison, and per-nucleotide kinetic estimates.
- transcript topics: XPD function in nucleotide excision repair and lesion verification; XPD domain architecture and DNA-binding groove; Seven-state ATPase cycle (S1–S7) and translocation on ssDNA; Constriction 1 (5′ end) and Constriction 2 (3′ end) as molecular clamps; ATP binding/hydrolysis and mechanical coupling (spring spindle helix, Arch/Fe–S interactions); Disease mutations: XP, CS, TTD phenotypes and class mapping

QC Summary:
- factual score: 10/10
- metadata score: 10/10
- supported core claims: 7
- claims flagged for review: 0
- metadata checks passed: 4
- metadata issues found: 0

Metadata Audited:
- article_doi
- article_title
- article_journal
- license

Factual Items Audited:
- XPD translocates 5′→3′ on ssDNA via a seven-state ATPase cycle (S1–S7).
- Two constrictions (Constriction 1 at the 5′ end and Constriction 2 at the 3′ end) act as molecular clamps enabling directional translocation.
- Mutations cluster at DNA-binding and ATPase sites and are categorized into three classes (A XP, B XP/CS, C XP/CS) with disease phenotypes XP, CS, and TTD.
- Key structural elements such as the spring helix and spindle helix couple motor-domain movements to Arch/Fe–S domains.
- XPD and DinG share a common architecture but differ in Fe–S domain anchoring; DinG lacks the XPD-specific anchoring element and shows different intermediate states (SD1–SD5).
- Per-nucleotide translocation times are predicted to be ~4 ms for XPD and ~9 ms for DinG; experimental rates on duplex DNA under load can be ~100 ms per nucleotide.

QC result: Pass.