B. subtilis MutS2 splits stalled ribosomes into subunits without mRNA cleavage

Area of Science:

• Molecular Biology
• Bacterial Protein Function
• Ribosome Biogenesis and Function

Background:

• Stalled ribosomes trigger cellular rescue pathways involving nascent polypeptide degradation and ribosome recycling.
• In Escherichia coli, ribosome collisions lead to mRNA cleavage by SmrB, facilitating rescue.
• The bacterial protein MutS2 in Bacillus subtilis has been suggested to play a role in ribosome rescue.

Purpose of the Study:

• To elucidate the molecular mechanism of MutS2 in Bacillus subtilis ribosome rescue.
• To determine how MutS2 interacts with collided ribosomes and mediates rescue.
• To compare the ribosome rescue pathway in B. subtilis with that in E. coli.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to visualize MutS2-ribosome interactions.
• In vivo and in vitro biochemical assays to study MutS2 activity.
• Analysis of MutS2 domains (SMR and KOW) and its ATPase function.

Main Results:

• MutS2 is recruited to collided ribosomes via its SMR and KOW domains.
• MutS2 utilizes its ABC ATPase activity to physically split collided ribosomes.
• MutS2 targets nascent peptides for degradation via the ribosome quality control pathway, without evidence of mRNA cleavage or tmRNA involvement.

Conclusions:

• MutS2 functions as a key player in Bacillus subtilis ribosome rescue by dissociating collided ribosomes.
• The mechanism differs from E. coli's SmrB, highlighting diversity in bacterial ribosome rescue pathways.
• Clarifies the biochemical and cellular roles of MutS2 in bacterial stress response and protein synthesis quality control.