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| Title | Structural transitions in the stepwise assembly of proteasome core particles. |
|---|---|
| Journal, issue, pages | Nat Commun, Vol. 17, Issue 1, Year 2026 |
| Publish date | Mar 24, 2026 |
Authors | Eric Mark / Paula C Ramos / Maria M Nunes / Ana C Matias / R Jürgen Dohmen / Petra Wendler / ![]() |
| PubMed Abstract | 20S catalytic core particles (CP) of eukaryotic 26S proteasomes are composed of two identical halves comprising 14 distinct subunits. 15S precursor complexes (PC) represent detectable half-CPs ...20S catalytic core particles (CP) of eukaryotic 26S proteasomes are composed of two identical halves comprising 14 distinct subunits. 15S precursor complexes (PC) represent detectable half-CPs assembly intermediates lacking the β7-subunit but containing assembly chaperones Ump1 and Pba1-Pba2. Incorporation of β7 drives 15S-PC dimerisation and further CP maturation. Our cryo-EM structures of the yeast 15S-PC and all 13S-PC-derived intermediates suggest that assembly in yeast is not restricted to a single trajectory, but instead involves alternative, and potentially simultaneous pathways. Comparison of the intermediates reveals how Ump1 and β-subunits become structured with each additionally incorporated β-subunit, and how this prepares peptidase sites for auto-activation. We identify two transient interactions of Pba1 with the α-ring, which are important for an ordered progression of maturation. Pba1 loop 81-117 intercalates between subunits α3 and α4 in 13S-15S-PCs and is displaced upon 15S-PC dimerisation. The second interaction involves the α1 N-terminus, deletion of which leads to a defect in Pba1-Pba2 release. These findings indicate how changes in α-ring subunit conformations coordinate CP maturation with Pba1‑Pba2 release. |
External links | Nat Commun / PubMed:41876489 / PubMed Central |
| Methods | EM (single particle) |
| Resolution | 3.09 - 4.11 Å |
| Structure data | EMDB-54029, PDB-9rl3: EMDB-54032, PDB-9rla: EMDB-54045, PDB-9rlt: EMDB-54046, PDB-9rlz: EMDB-54047, PDB-9rm0: EMDB-54048, PDB-9rm1: |
| Source |
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Keywords | HYDROLASE / proteasome biogenesis / Ump1 / Pba1-2 / cryo-EM |
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