Bidirectional effectors of a group I intron ribozyme

Area of Science:

• Molecular Biology
• Biochemistry
• RNA Biology

Background:

• Group I self-splicing introns are crucial genetic elements found across diverse organisms.
• L-arginine is known to competitively inhibit these introns.
• The specific mechanisms and stereoselectivity of L-arginine's interaction with group I introns require further elucidation.

Purpose of the Study:

• To investigate the stereoselective effects of L-arginine on the Pneumocystis carinii group I intron (Pc1. LSU).
• To determine the role of the guanidine moiety of arginine in its interaction with the ribozyme.
• To explore the potential of arginine derivatives as modulators of ribozyme activity.

Main Methods:

• Enzymatic assays using the Pc1. LSU nuclear group I intron.
• Kinetic analysis of splicing steps (cleavage and ligation).
• Inhibition and stimulation studies with L-arginine, L-canavanine, and various arginine derivatives (amides, esters, peptides).
• Use of pentamidine to block the first splicing step for enhanced observation of the second step.

Main Results:

• L-arginine competitively inhibits the first (cleavage) step and stimulates the second (ligation) step of splicing in a stereoselective manner.
• The guanidine group of arginine is essential for both inhibition and stimulation.
• Arginine derivatives, particularly di-arginine amide and tri-arginine, exhibit significantly enhanced inhibitory and stimulatory effects compared to L-arginine.
• Potent arginine peptides were found to be up to 10,000 times more effective inhibitors and 400 times more effective stimulators than L-arginine.

Conclusions:

• Arginine and its derivatives bind to specific sites on the ribozyme, altering its conformation.
• These conformational changes enhance the second splicing step while competing with guanosine for the first step.
• Ribozymes can be modulated by non-substrate small molecules, similar to protein enzymes.
• This suggests the potential development of arginine-based compounds as novel pharmacological agents targeting RNA molecules.