Structure of the TXNL1-bound proteasome

Area of Science:

• Cellular Biology
• Structural Biology
• Biochemistry

Background:

• Proteasomes are crucial for protein homeostasis, degrading proteins via regulated mechanisms.
• The precise regulation of proteasomal degradation, especially in response to cellular stress, remains incompletely understood.
• Thioredoxin-like protein 1 (TXNL1) is involved in cellular responses, but its proteasomal degradation pathway is unclear.

Purpose of the Study:

• To elucidate the structural basis of TXNL1 interaction with the proteasome.
• To understand the mechanism of TXNL1 degradation in response to oxidative stress.
• To identify the proteasomal subunits involved in TXNL1 recognition.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structure of TXNL1 bound to the 19S proteasome regulatory particle.
• Biochemical assays to assess TXNL1 degradation in cellular contexts.
• Identification of protein-protein interactions between TXNL1 and proteasome subunits.

Main Results:

• The cryo-EM structure reveals TXNL1 bound to the 19S regulatory particle of the proteasome.
• Key interactions involve TXNL1 binding to proteasome subunits PSMD1 (Rpn2), PSMD4 (Rpn10), and PSMD14 (Rpn11).
• Proteasome binding is essential for the ubiquitin-independent degradation of TXNL1 when cells are exposed to metal- or metalloid-induced oxidative stress.

Conclusions:

• The study establishes a structural requirement for the stress-induced degradation of TXNL1.
• This work uncovers a novel pathway for proteasomal degradation that is independent of ubiquitination.
• The findings provide a structural framework for understanding how proteasomes target specific proteins during cellular stress.