Guanidine-sensing riboswitches: How do they work and what do they regulate?

Area of Science:

• Molecular Biology
• Bacterial Physiology
• RNA Biology

Background:

• The ykkC riboswitch family, including ykkC, mini-ykkC, and ykkC-III, were orphan elements for over a decade.
• These riboswitches are now characterized as guanidine-specific genetic regulatory elements (guanidine-I, II, and III).

Purpose of the Study:

• To elucidate the function and structural basis of the newly characterized guanidine riboswitches.
• To explore the physiological significance of intracellular guanidine level regulation in bacteria.

Main Methods:

• Structural biology techniques, including X-ray crystallography, were employed to determine the atomic structures of the guanidine riboswitches.
• Biochemical and genetic assays were likely used to confirm guanidine specificity and regulatory function.

Main Results:

• The crystal structures of all three guanidine riboswitch family members have been determined, revealing distinct tertiary folds.
• Despite structural diversity, a conserved guanidine-binding core was identified across the family.
• These riboswitches activate genes involved in guanidine export and breakdown in response to elevated intracellular guanidine.

Conclusions:

• The ykkC riboswitch family represents independently evolved RNA sensors with a conserved guanidine-binding mechanism.
• The discovery highlights the importance of regulating intracellular guanidine levels in bacterial physiology.
• Further research is needed to identify guanidine-producing metabolic pathways and the function of non-guanidine-sensing relatives.