RNase E resolves toxic condensates by counteracting phase separation of Type II RhlB helicases

Area of Science:

• Molecular Biology
• Microbiology
• Biochemistry

Background:

• The RNA degradosome complex, including RNA helicase RhlB and scaffold endoribonuclease RNase E, is crucial for RNA processing and degradation in Proteobacteria.
• In Escherichia coli (Type I RhlB), RNase E allosterically activates RhlB, establishing a regulatory paradigm.

Purpose of the Study:

• To investigate a distinct clade of RhlB helicases (Type II), exemplified by Pseudomonas aeruginosa RhlB.
• To elucidate the regulatory mechanism of Type II RhlB by its cognate RNase E and its role in bacterial physiology.

Main Methods:

• Biochemical assays
• Structural analyses
• Functional studies of P. aeruginosa RhlB and RNase E interactions
• Assessment of bacterial growth under varying temperatures

Main Results:

• Type II RhlB helicases possess an N-terminal intrinsically disordered region promoting RNA-dependent liquid-liquid phase separation and enhanced activity.
• P. aeruginosa RNase E interacts with RhlB via a unique interface, antagonizing phase separation rather than activating it.
• Excessive RhlB condensation inhibits bacterial growth at low temperatures, a process modulated by RNase E.

Conclusions:

• Conserved RNA degradosome components exhibit divergent regulatory interactions across species.
• Condensate dissolution by RNase E represents a novel mechanism for regulating RNA helicase activity and bacterial growth.
• This study reveals species-specific regulation of RNA helicase function within the RNA degradosome.