324: ZSWIM8–CUL3 clamp on AGO2–miR-7 reveals mechanism of targeted microRNA degradation

Farnung J et al., Nature - Cryo-EM and biochemical reconstitution reveal how the ZSWIM8–CUL3 E3 ligase recognizes human AGO2–miRNA–trigger complexes to polyubiquitylate AGO and drive targeted microRNA degradation. Key terms: ZSWIM8, AGO2, target-directed miRNA degradation, cryo-EM structure, E3 ubiquitin ligase.

Study Highlights:
Using purified human proteins and cellular assays, the authors combined cryo-EM (3.1 Å), in vitro ubiquitylation, co-immunoprecipitation and sRNA-seq to dissect TDMD. Cryo-EM shows a dimeric ZSWIM8 that forms an asymmetric clamp around AGO2–miR-7–CYRANO, engaging the MID, N and PAZ domains and embracing trigger RNA flanks. Biochemical reconstitution demonstrates that ZSWIM8–CUL3 together with ARIH1 polyubiquitylates surface lysines of AGO only when the miRNA is paired to a trigger that vacates the PAZ pocket and imposes a specific RNA trajectory. Functionally, these multivalent RNA–RNA, RNA–protein and protein–protein interactions establish a two-RNA-factor authentication mechanism that explains TDMD selectivity and indicates ZSWIM8 can destabilize extensively trimmed miRNAs.

Conclusion:
ZSWIM8–CUL3 recognizes a trigger-induced AGO–miRNA conformation via multivalent interactions—including sensing a vacated PAZ pocket and flanking trigger RNA—to direct ARIH1-dependent polyubiquitylation of AGO and execute TDMD.

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

Article title:
The E3 ubiquitin ligase mechanism specifying targeted microRNA degradation

First author:
Farnung J

Journal:
Nature

DOI:
10.1038/s41586-026-10232-0

Reference:
Farnung J., Slobodyanyuk E., Wang P.Y., Blodgett L.W., Lin D.H., von Gronau S., Schulman B.A. & Bartel D.P. The E3 ubiquitin ligase mechanism specifying targeted microRNA degradation. Nature (2026). https://doi.org/10.1038/s41586-026-10232-0

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/

Support:
Base by Base – Stripe donations: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00

Official website https://basebybase.com

On PaperCast Base by Base you’ll discover the latest in genomics, functional genomics, structural genomics, and proteomics.

Episode link: https://basebybase.com/episodes/zswim8-cul3-tdmd-structure

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-03-23.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music
- transcript coverage: Audited the transcript portions describing TDMD mechanism, ZSWIM8–CUL3 E3 ligase architecture, AGO2–miRNA–trigger complex recognition, CYRANO/HSUR1 triggers, RNA flanking regions and RBEs, PAZ-pocket vacancy, dimeric clamp, and broader biological implications.
- transcript topics: TDMD overview and cellular context; ZSWIM8–CUL3 E3 ligase architecture and dimer clamp; AGO2–miRNA–trigger complex recognition by ZSWIM8; Trigger RNAs (CYRANO, HSUR1) and pairing architecture; RNA flanking regions and RBEs in ZSWIM8 binding; PAZ pocket vacancy and RNA trajectory

QC Summary:
- factual score: 10/10
- metadata score: 10/10
- supported core claims: 8
- 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:
- TDMD is mediated by ZSWIM8–CUL3 E3 ligase polyubiquitylating AGO2–miRNA in the presence of a trigger RNA
- ZSWIM8 preferentially binds AGO–miRNA–trigger ternaries over AGO–miRNA–seed-only complexes
- ZSWIM8 operates as a dimer that clamps around the AGO2–miR-7–CYRANO complex
- Trigger RNA-induced conformational changes expose an unoccupied PAZ pocket that is recognized by ZSWIM8
- RNA flanking regions and RBEs contribute to ZSWIM8 recognition and binding efficiency
- Two-RNA-factor authentication model: miRNA as password, trigger RNA as phone ping

QC result: Pass.