New macrocyclic terbium(III) complex for use in RNA footprinting experiments

Area of Science:

• Coordination Chemistry
• Bioinorganic Chemistry
• RNA Catalysis

Background:

• Development of synthetic nucleases is crucial for understanding and manipulating RNA. Lanthanide complexes offer potential as catalysts due to their Lewis acidity and coordination versatility.
• Cyclen derivatives provide robust coordination environments for metal ions, influencing their catalytic activity and stability.

Purpose of the Study:

• To synthesize and characterize a novel terbium complex with a heptadentate cyclen derivative (L1) for RNA cleavage applications.
• To investigate the catalytic activity of the terbium complex in RNA phosphodiester bond hydrolysis and its mechanism.
• To explore the utility of the terbium complex in RNA footprinting assays.

Main Methods:

• Synthesis and X-ray crystal structure determination of the terbium complex [Tb(L1)(OTf)(OH2)] (C1).
• Kinetic studies of RNA cleavage using model phosphodiesters (UpNP) and RNA transcripts (HIV-1 TAR, DIS, A-site, tRNA(fMet)).
• RNA footprinting experiments to assess binding interactions with RNA structures.

Main Results:

• The synthesized complex [Tb(L1)(OTf)(OH2)] (C1) features a 9-coordinate terbium(III) center with a capped square-antiprism geometry.
• The active species in water, [Tb(L1)(OH2)2](3+), exhibits significant catalytic activity in RNA transesterification (k_obs = 5.5 x 10(-2) s(-1) for UpNP).
• The complex selectively cleaves single-stranded RNA regions and was successfully used in footprinting to confirm peptide and small molecule binding.

Conclusions:

• The heptadentate ligand L1 effectively stabilizes the terbium(III) ion, creating a potent synthetic ribonuclease.
• The presence of labile water ligands is essential for the catalytic activity of the terbium complex in RNA cleavage.
• The selectivity of the terbium complex for single-stranded RNA makes it a valuable tool for studying RNA-protein and RNA-ligand interactions.