A gated channel into the proteasome core particle

Area of Science:

• * Molecular biology
• * Structural biology
• * Biochemistry

Background:

• * The proteasome is a large protein complex essential for cellular protein homeostasis.
• * The core particle (CP) of the proteasome is a barrel-shaped structure composed of seven-membered rings.
• * The yeast proteasome core particle (CP) is known to be regulated.

Purpose of the Study:

• * To investigate the autoinhibition mechanism of the yeast proteasome core particle (CP).
• * To elucidate the role of N-terminal tails of alpha-ring subunits in CP regulation.
• * To understand how the proteasome holoenzyme is formed and activated.

Main Methods:

• * Crystallographic analysis of the yeast proteasome core particle (CP).
• * Site-directed mutagenesis to delete N-terminal tails of alpha-ring subunits.
• * Biochemical assays to measure peptide hydrolysis activity.

Main Results:

• * The N-terminal tails of the outer alpha-ring subunits autoinhibit the yeast proteasome core particle (CP).
• * Deletion of the alpha 3-subunit N-terminal tail opens the CP's central channel, derepressing peptide hydrolysis.
• * The alpha-subunit tails maintain the CP in a latent state by blocking substrate entry.
• * Binding of the regulatory particle to the CP relieves inhibition, forming the active proteasome holoenzyme.

Conclusions:

• * The N-terminal tails of alpha-ring subunits act as gatekeepers, controlling substrate access to the yeast proteasome core particle (CP).
• * Proteolytic activity is regulated by conformational changes involving these tails and the assembly of the proteasome holoenzyme.
• * Understanding this regulatory mechanism is crucial for comprehending proteasome function in cellular protein degradation.