RING dimerisation drives higher‐order organisation of SINA/SIAH E3 ubiquitin ligases

• DOI: 10.1111/febs.70000
• Publication Date: 2025-02-06T04:33:41Z
• Authors: Franck Coste; Aanchal Mishra; Catherine Chapuis; Lucija Mance; Zofia Pukało; Nicolas Bigot; Stéphane Goffinont; Virginie Gaudon; Norbert Garnier; Ibtissam Talhaoui; Bertrand Castaing; Sebastien Huet; Marcin J. Suskiewicz
• Keywords: Ubiquitin-Protein Ligases; RING finger domain; Ring finger

RING‐type E3 ubiquitin ligases promote ubiquitylation by stabilising an active complex between a ubiquitin‐loaded E2‐conjugating enzyme and protein substrate. To fulfil this function, the ubiquitin‐protein ligase SIAH1 other SINA/SIAH subfamily employ N‐terminal catalytic RING domain C‐terminal substrate‐binding (SBD), separated two zinc fingers. Here, we present first crystal structure of human SIAH1, together with adjacent finger, revealing potential dimer, which was validated in solution using static light scattering. dimerisation contributes to activity both vitro cells. Moreover, as is second element, after SBD, independently favour homodimerisation within ligases, propose that alternating RING:RING SBD:SBD interactions organise multiple copies into higher‐order homomultimer. In line hypothesis, fluorescently tagged full‐length SIAH2 fruit fly SINA show cytoplasmic clusters cells, whereas their distribution becomes more diffuse when disabled. The wild‐type (WT) form but not its mutant, colocalises aggregated synphilin‐1A under proteasomal inhibition, suggesting multimerisation might contribute reported preference for or multimeric substrates.