An atomic structure of the human 26S proteasome

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Cell Biology

Background:

• The 26S proteasome is a crucial multi-subunit protease complex responsible for regulated protein degradation in eukaryotic cells.
• Understanding its structure is key to elucidating its function in various cellular processes and diseases.

Purpose of the Study:

• To determine the high-resolution cryo-electron microscopy (cryo-EM) structure of the human 26S proteasome.
• To provide atomic-level insights into the interactions between the core particle (CP) and regulatory particle (RP).
• To visualize the nucleotide-bound state of the proteasome and its implications for substrate translocation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to obtain high-resolution structural data.
• Atomic modeling was performed to build detailed subunit structures within the proteasome complex.
• Structural analysis focused on subunit interactions, nucleotide binding, and channel gating mechanisms.

Main Results:

• The cryo-EM structure of the human 26S proteasome was resolved to an average of 3.5 Å, enabling atomic modeling of 28 CP and 18 RP subunits.
• Specific interactions were observed between RP subunits (Rpt3, Rpt5) and CP α subunits.
• Nucleotide binding was confirmed in all six Rpt subunits, and the CP gate remained closed upon RP association.
• The pore 1 loops form a spiral staircase, and pore 2 loops constrict the axial channel, influencing substrate transport.

Conclusions:

• The determined structures offer unprecedented atomic detail of the human 26S proteasome.
• These findings provide a structural basis for understanding substrate entry, gating, and the role of nucleotide binding in proteasome regulation.
• The study lays the groundwork for future mechanistic investigations into proteasome function and its modulation by associated factors like USP14.