A ubiquitin chain-feeding mechanism for BRCA1-A.

Authors

Andrea G Murachelli, Farid El Oualid, Titia K Sixma

Published in

Nature communications. Volume 17. Issue 1. Aug 11, 2026. Epub Aug 11, 2026.

Abstract

The BRCA1-A complex is a multi-subunit, metallo-deubiquitinating enzyme (metallo-DUB) involved in genome maintenance. BRCA1-A displays strict specificity for K63-linked ubiquitin, with a strong preference for long chains, but the mechanistic basis for this selectivity has remained unclear. To address this, we have developed an activity-based probe that is specific for metallo-DUBs and mimics di- or polyubiquitin chains of any linkage (di- and poly-ubiquitin_ATA). We have solved cryoEM structures of BRCA1-A bound to K63-linked probe chains of various length, capturing multiple conformational and catalytic states. The structures reveal how allosteric regulation of catalysis occurs within the complex and how BRCA1-A uses auxiliary ubiquitin-binding sites to engage substrate by avidity and to trigger processive cleavage. Crucially, avidity and processivity can only apply to long polyubiquitin chains, explaining BRCA1-A's substrate preference. Together, these results establish BRCA1-A as a chain-shortening DUB specialised for trimming extended K63-linked polyubiquitin chains.

PMID:
42581048
Bibliographic data and abstract were imported from PubMed on 12 Aug 2026.

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