Structure of a Cytoplasmic 11-Subunit RNA Exosome Complex

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The RNA exosome complex is crucial for RNA metabolism, involving transcript decay, surveillance, and processing.
• In the cytoplasm, the exosome core (Exo10) interacts with the Ski complex, mediated by the cofactor Ski7 in yeast.
• Understanding the structural basis of these interactions is key to elucidating cytoplasmic RNA processing pathways.

Purpose of the Study:

• To determine the high-resolution structure of the Saccharomyces cerevisiae Exo10 and Ski7 complex.
• To elucidate the molecular interactions stabilizing the cytoplasmic exosome complex.
• To investigate the evolutionary conservation of Ski7-like cofactors in exosome function.

Main Methods:

• X-ray crystallography was employed to determine the structure of the S. cerevisiae Exo10-Ski7 complex at 2.65 Å resolution.
• Biochemical analyses were used to characterize the interactions and stability of the complex.
• Comparative sequence and structural analysis was performed to identify homologous proteins and conserved motifs.

Main Results:

• The crystal structure reveals extensive hydrophobic interactions between Exo10 and the interacting domain of Ski7, explaining the complex's high affinity and stability.
• Ski7 is identified as a constitutive component of the cytosolic exosome.
• Similar binding surfaces and recognition motifs are used by cytoplasmic Ski7 and nuclear Rrp6 to bind Exo10, despite lacking sequence homology.
• A human HBS1-Like splice variant was identified as a Ski7-like exosome-binding protein, demonstrating evolutionary conservation.

Conclusions:

• The structure of the Exo10-Ski7 complex provides critical insights into the molecular mechanisms of cytoplasmic RNA decay.
• Ski7 plays a fundamental role in the stability and function of the cytosolic RNA exosome.
• The conserved binding interface highlights an ancient mechanism for exosome cofactor interaction, extending from yeast to humans.