9PF1

Nub1/Fat10-processing human 26S proteasome with Rpt4 at top of spiral staircase (AAA+ motor locally refined)

This is a non-PDB format compatible entry.

Summary for 9PF1

• Entry DOI: 10.2210/pdb9pf1/pdb
• EMDB information: 71584
• Descriptor: 26S proteasome regulatory subunit 7, Substrate polypeptide, 26S proteasome regulatory subunit 4, ... (19 entities in total)
• Functional Keywords: 26s proteasome, motor protein, hydrolase-protein binding complex
• Biological source: Homo sapiens (human); More
• Total number of polymer chains: 15
• Total formula weight: 530671.82

Authors

Arkinson, C.,Gee, C.L.,Martin, A. (deposition date: 2025-07-03, release date: 2025-11-19)

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., 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 (3.57 Å)