9RL3

13S proteasome precursor complex

Summary for 9RL3

• Entry DOI: 10.2210/pdb9rl3/pdb
• EMDB information: 54029
• Descriptor: Proteasome subunit alpha type-1, Probable proteasome subunit alpha type-7, Proteasome subunit beta type-2, ... (13 entities in total)
• Functional Keywords: proteasome biogenesis, ump1, pba1-2, cryo-em, hydrolase
• Biological source: Saccharomyces cerevisiae (brewer's yeast); More
• Total number of polymer chains: 13
• Total formula weight: 351868.15

Authors

Mark, E.,Ramos, P.C.,Nunes, M.M.,Dohmen, R.J.,Wendler, P. (deposition date: 2025-06-16, release date: 2026-03-18, Last modification date: 2026-04-01)

Primary citation

Mark, E.,Ramos, P.C.,Nunes, M.M.,Matias, A.C.,Jurgen Dohmen, R.,Wendler, P.
Structural transitions in the stepwise assembly of proteasome core particles.
Nat Commun, 17:-, 2026

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 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.

PubMed: 41876489
DOI: 10.1038/s41467-026-70525-w

Experimental method

ELECTRON MICROSCOPY (3.31 Å)