9E8L

Nub1/Fat10-processing human 26S proteasome bound to Txnl1 with Rpt4 at top of spiral staircase

Summary for 9E8L

• Entry DOI: 10.2210/pdb9e8l/pdb
• EMDB information: 47724
• Descriptor: 26S proteasome regulatory subunit 7, Proteasome subunit alpha type-7, Proteasome subunit alpha type-5, ... (32 entities in total)
• Functional Keywords: 26s proteasome, nub1, fat10, motor protein, hydrolase-protein binding complex, hydrolase/protein binding
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 28
• Total formula weight: 1214679.72

Authors

Arkinson, C.,Gee, C.L.,Martin, A. (deposition date: 2024-11-05, release date: 2024-12-04, Last modification date: 2025-12-24)

Primary citation

Arkinson, C.,Gee, C.L.,Zhang, Z.,Dong, K.C.,Martin, A.
Structural landscape of the degrading 26S proteasome reveals conformation-specific binding of TXNL1.
Nat.Struct.Mol.Biol., 32:2403-2415, 2025

PubMed Abstract: The 26S proteasome targets many cellular proteins for degradation during homeostasis and quality control. Proteasome-interacting cofactors modulate these functions and aid in substrate degradation. Here we solve high-resolution structures of the redox active cofactor TXNL1 bound to the human 26S proteasome at saturating and substoichiometric concentrations by time-resolved cryo-electron microscopy (cryo-EM). We identify distinct binding modes of TXNL1 that depend on the proteasome conformation and ATPase motor states. Together with biophysical and biochemical experiments, we show that the resting-state proteasome binds TXNL1 with low affinity and in variable positions on top of the Rpn11 deubiquitinase. In contrast, in the actively degrading proteasome, TXNL1 uses additional interactions for high-affinity binding, whereby its C-terminal tail covers the catalytic groove of Rpn11 and coordinates the active-site Zn. Furthermore, these cryo-EM structures of the degrading proteasome capture the ATPase hexamer in several spiral-staircase arrangements that indicate temporally asymmetric hydrolysis and conformational changes in bursts during mechanical substrate unfolding and translocation. Remarkably, we catch the proteasome in the act of unfolding the β-barrel mEos3.2 substrate while the ATPase hexamer is in a particular staircase register. Our findings advance current models for protein translocation through hexameric AAA+ motors and reveal how the proteasome uses its distinct conformational states to coordinate cofactor binding and substrate processing.

PubMed: 41198955
DOI: 10.1038/s41594-025-01695-2

Experimental method

ELECTRON MICROSCOPY (3.59 Å)