Na⁺ riboswitches regulate genes for diverse physiological processes in bacteria

Area of Science:

• Molecular Biology
• Microbiology
• Biochemistry

Background:

• Organisms possess mechanisms to adapt to cellular sodium (Na+) concentration changes.
• Previously, only one bacterial protein was known to selectively sense Na+ and regulate gene expression.

Purpose of the Study:

• To identify and characterize a novel class of riboswitches that selectively sense Na+.
• To understand the role of these Na+-sensing riboswitches in regulating genes related to sodium biology and osmotic stress.

Main Methods:

• Identification of the 'DUF1646 motif' as a Na+-sensing riboswitch class.
• Biochemical assays to determine dissociation constants and ion selectivity.
• Analysis of gene expression changes mediated by Na+ riboswitches.

Main Results:

• A novel class of riboswitches, termed Na+-riboswitches, selectively sense Na+ with low mM dissociation constants.
• These riboswitches regulate genes involved in metal ion transport, osmotic stress mitigation, and ATP production via Na+ gradients.
• Na+ riboswitches demonstrate high selectivity, rejecting other alkali and alkaline earth ions, and only Na+ triggers gene expression changes.
• Na+-riboswitches were observed to collaborate with cyclic di-AMP (c-di-AMP) riboswitches to coordinate gene expression during osmotic stress.

Conclusions:

• Bacteria utilize Na+-riboswitches to monitor, adjust, and exploit cellular Na+ concentrations and gradients.
• These riboswitches represent a significant mechanism for bacterial adaptation to environmental sodium levels.
• The findings highlight the intricate regulatory networks bacteria employ to manage osmotic balance and energy production.