Structural basis of prokaryotic ubiquitin-like protein engagement and translocation by the mycobacterial...

Area of Science:

• Structural Biology
• Microbiology
• Biochemistry

Background:

• Proteasomes are crucial for protein degradation in eukaryotes, archaea, and Actinobacteria.
• In Mycobacterium tuberculosis, proteasomal degradation is vital for pathogen persistence.
• Prokaryotic ubiquitin-like protein (Pup) tags substrates for degradation by the mycobacterial proteasome.

Purpose of the Study:

• To elucidate the mechanism of substrate translocation into the mycobacterial proteasome.
• To determine the structure of the mycobacterial proteasome ATPase (Mpa) in complex with the 20S core particle.
• To understand the role of Mpa's structural features in substrate movement.

Main Methods:

• Single-particle cryo-electron microscopy (cryo-EM) was used to determine the structure of Mpa bound to the 20S core particle.
• In vitro and in vivo experiments were conducted to validate findings.

Main Results:

• The study captured Mpa at an early stage of pupylated substrate recruitment.
• Two distinct conformational states of Mpa were identified, illustrating stepwise substrate translocation.
• A key structural feature of Mpa facilitates charge-complementary interactions, enabling radial, guided movement.

Conclusions:

• The findings provide atomic-level insight into the mechanism of substrate translocation by the mycobacterial proteasome.
• This structural understanding of Mpa's function is critical for comprehending Mycobacterium tuberculosis persistence.
• The identified mechanism highlights the importance of specific interactions for protein degradation machinery.