Structural characterization of a eukaryotic chaperone--the ribosome-associated complex

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Ribosome-associated chaperones are crucial for early protein folding during synthesis.
• While prokaryotic chaperones are well-studied, eukaryotic counterparts remain less understood structurally.
• The eukaryotic ribosome-associated complex (RAC) is composed of Hsp70 Ssz1 and Hsp40 Zuo1.

Purpose of the Study:

• To elucidate the structural basis of eukaryotic ribosome-associated complex (RAC) function.
• To understand the interaction of RAC with the ribosome and its role in protein synthesis.

Main Methods:

• Presented structural analyses of the eukaryotic RAC from Saccharomyces cerevisiae and Chaetomium thermophilum.
• Utilized X-ray crystallography to determine the structure of the Ssz1 ATPase domain bound to ATP-Mg²⁺.

Main Results:

• RAC adopts an elongated conformation over the ribosomal tunnel exit, stabilized by expansion segment ES27.
• A unique α-helical domain in Zuo1 mediates RAC's ribosome interaction near specific ribosomal proteins and rRNA.
• The crystal structure reveals Ssz1's ATPase domain is catalytically inactive, suggesting a pre-chaperone role.

Conclusions:

• The study provides novel structural insights into the eukaryotic RAC.
• Findings suggest Ssz1 acts upstream of the RAC-associated chaperone Ssb.
• This work illuminates the interplay between RAC, ERj1, and the signal-recognition particle in protein synthesis.