Download MendeleyStructural landscape of the degrading 26S proteasome reveals conformation-specific binding of TXNL1.
Arkinson, C., Gee, C.L., Zhang, Z., Dong, K.C., Martin, A.(2025) Nat Struct Mol Biol
- PubMed: 41198955
- DOI: https://doi.org/10.1038/s41594-025-01695-2
- Primary Citation of Related Structures:
9E8G, 9E8H, 9E8I, 9E8J, 9E8K, 9E8L, 9E8N, 9E8O, 9E8Q, 9PDI, 9PDL, 9PDN, 9PF1 - 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 2+ . 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.
- California Institute for Quantitative Biosciences, University of California at Berkeley, Berkeley, CA, USA.
Organizational Affiliation:
