8USD

Rpn1/Nub1UBL-focused alignment of the non-substrate-engaged human 26S proteasome

Summary for 8USD

• Entry DOI: 10.2210/pdb8usd/pdb
• EMDB information: 42508
• Descriptor: 26S proteasome non-ATPase regulatory subunit 2, NEDD8 ultimate buster 1, 26S proteasome regulatory subunit 7, ... (5 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: 5
• Total formula weight: 333810.35

Authors

Arkinson, C.,Gee, C.L.,Martin, A. (deposition date: 2023-10-27, release date: 2024-11-06, Last modification date: 2025-04-23)

Primary citation

Arkinson, C.,Dong, K.C.,Gee, C.L.,Costello, S.M.,Soe, A.C.,Hura, G.L.,Marqusee, S.,Martin, A.
NUB1 traps unfolded FAT10 for ubiquitin-independent degradation by the 26S proteasome.
Nat.Struct.Mol.Biol., 2025

PubMed Abstract: The ubiquitin-like modifier FAT10 targets hundreds of proteins in the mammalian immune system to the 26S proteasome for degradation. This degradation pathway requires the cofactor NUB1, yet the underlying mechanisms remain unknown. Here, we reconstituted a minimal in vitro system with human components and revealed that NUB1 uses the intrinsic instability of FAT10 to trap its N-terminal ubiquitin-like domain in an unfolded state and deliver it to the 26S proteasome for engagement, allowing the degradation of FAT10-ylated substrates in a ubiquitin-independent and p97-independent manner. Using hydrogen-deuterium exchange, structural modeling and site-directed mutagenesis, we identified the formation of an intricate complex with FAT10 that activates NUB1 for docking to the 26S proteasome, and our cryo-EM studies visualized the highly dynamic NUB1 complex bound to the proteasomal Rpn1 subunit during FAT10 delivery and the early stages of ATP-dependent degradation. These findings identified a previously unknown mode of cofactor-mediated, ubiquitin-independent substrate delivery to the 26S proteasome that relies on trapping partially unfolded states for engagement by the proteasomal ATPase motor.

PubMed: 40217121
DOI: 10.1038/s41594-025-01527-3

Experimental method

ELECTRON MICROSCOPY (2.7 Å)