Mg(2+)-induced conformational changes in the btuB riboswitch from E. coli

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Riboswitches regulate gene expression in response to small molecules.
• The btuB riboswitch from E. coli controls the expression of the BtuB transporter protein, regulating cellular coenzyme B12 (adenosyl-cobalamine, AdoCbl) levels.

Purpose of the Study:

• To investigate the structural folding of the E. coli btuB riboswitch in response to magnesium ions (Mg2+).
• To determine how Mg2+ concentration influences the riboswitch's conformational states and ligand-binding competence.

Main Methods:

• In-line probing was used to identify distinct RNA conformations.
• Analysis of riboswitch behavior at varying Mg2+ concentrations.

Main Results:

• The btuB riboswitch exists in at least two Mg2+-dependent conformations.
• A specific conformation, essential for ligand binding, is adopted above ~0.5 mM Mg2+.
• Mg2+ is critical for enabling the AdoCbl-induced conformational switch.

Conclusions:

• Magnesium ions play a vital role in stabilizing the active conformation of the btuB riboswitch.
• The stepwise folding of the btuB RNA, driven by increasing Mg2+ concentration, is essential for its regulatory function.