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TitleStructures of the 26 proteasome in complex with the Hsp70 co-chaperone Bag1 reveal a mechanism for direct substrate transfer.
Journal, issue, pagesSci Adv, Vol. 12, Issue 8, Page eadz3026, Year 2026
Publish dateFeb 20, 2026
AuthorsMoisés Maestro-López / Tat Cheung Cheng / Jimena Muntaner / Margarita Menéndez / Melissa Alonso / Andreas Schweitzer / Masato Ishizaka / Robert J Tomko / Jorge Cuéllar / José María Valpuesta / Eri Sakata /
PubMed AbstractCoupling between the chaperone and degradation systems, particularly under stress, is essential for eliminating unfolded proteins. The co-chaperone Bag1 links Hsp70 to the 26 proteasome, recruiting ...Coupling between the chaperone and degradation systems, particularly under stress, is essential for eliminating unfolded proteins. The co-chaperone Bag1 links Hsp70 to the 26 proteasome, recruiting Hsp70-bound clients for proteasomal degradation. Here, we present cryo-electron microscopy structures of the Bag1-bound 26 proteasome, revealing unprecedented conformational rearrangements within the 19 regulatory particle. Bag1 binding to the Rpn1 induces a marked reconfiguration of AAA adenosine triphosphatase (ATPase) ring, disrupting its canonical spiral staircase and remodeling the central channel architecture. This reconfiguration generates a large cavity above the substrate entry gate of the 20 core particle. The conserved pore-2 loops of ATPases Rpt2 and Rpt5 play critical roles in opening of the 20 gate, enabling substrate entry into proteolytic chamber independently of ubiquitination. These findings suggest a previously unknown mechanism of the proteasomal degradation, by which remodeling the central cavity and 20 gate in the presence of Bag1, possibly bypassing the need for ubiquitination.
External linksSci Adv / PubMed:41719407 / PubMed Central
MethodsEM (single particle)
Resolution3.5 - 6.2 Å
Structure data

52097

9heu

EMDB-52097, PDB-9heu:
Co-chaperone Bag1-bound human 26S proteasome in SBAG1 state
Method: EM (single particle) / Resolution: 3.6 Å

52193

9szt

EMDB-52193: Co-chaperone Bag1-bound human 26S proteasome in SBAG2 state
PDB-9szt: Co-chaperone Bag1-bound human 26S proteasome in SBAG1.2 state
Method: EM (single particle) / Resolution: 3.5 Å

52194

9szv

EMDB-52194: Co-chaperone Bag1-bound human 26S proteasome in SBAG3 state
PDB-9szv: Co-chaperone Bag1-bound human 26S proteasome in SBAG1.3 state
Method: EM (single particle) / Resolution: 3.5 Å

EMDB-52195: Hsp70-NBD:Bag1:Rpn1 ternary complex class 1
Method: EM (single particle) / Resolution: 4.8 Å

EMDB-52196: Hsp70-NBD:Bag1:Rpn1 ternary complex class 2
Method: EM (single particle) / Resolution: 6.2 Å

EMDB-53945: Co-chaperone Bag1-bound human 26S proteasome in SBag2 state
Method: EM (single particle) / Resolution: 3.7 Å

Chemicals

ChemComp-ATP:
ADENOSINE-5'-TRIPHOSPHATE / ATP, energy-carrying molecule*YM

ChemComp-ADP:
ADENOSINE-5'-DIPHOSPHATE / ADP, energy-carrying molecule*YM

Source
  • homo sapiens (human)
KeywordsHYDROLASE / Protein degradation / protease / AAA+ ATPase / Hsp70 / cochaperone / Bag1 / Complex / ubiquitin

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