Cooperative and anticooperative binding to a ribozyme

Area of Science:

• Biochemistry
• Molecular Biology
• RNA Catalysis

Background:

• Ribozymes are catalytic RNA molecules with diverse biological functions.
• Understanding ligand interactions with ribozymes is crucial for elucidating their catalytic mechanisms.
• The Tetrahymena thermophila ribozyme serves as a model system for studying RNA structure and function.

Purpose of the Study:

• To investigate the thermodynamic and kinetic effects of guanosine 5'-monophosphate (GMP) and 2'-deoxyguanosine 5'-monophosphate (dGMP) on pyrene-labeled 5' exon mimic (pyCUCU) binding to the Tetrahymena thermophila ribozyme.
• To elucidate the mechanisms underlying cooperative and anticooperative binding effects induced by GMP and dGMP.
• To confirm that observed effects are not artifacts of the pyrene label, salt concentration, or ribozyme renaturation protocols.

Main Methods:

• Fluorescence titration experiments to determine binding thermodynamics.
• Kinetics experiments to analyze binding and dissociation rates.
• Utilized a pyrene-labeled 5' exon mimic (pyCUCU) and an L-21 Sca I-truncated ribozyme from Tetrahymena thermophila.
• Performed experiments at a controlled temperature of 15 degrees C.

Main Results:

• GMP binding to the ribozyme is anticooperative, weakening pyCUCU binding by a factor of 5.
• dGMP binding to the ribozyme is cooperative, strengthening pyCUCU binding by a factor of 4.
• GMP-induced anticooperativity is linked to slower formation of tertiary contacts.
• dGMP-induced cooperativity is linked to slower disruption of tertiary contacts.

Conclusions:

• GMP and dGMP exert significant, opposing effects on ribozyme-ligand interactions.
• These nucleotides modulate ribozyme function by influencing the dynamics of tertiary contact formation and disruption.
• The observed effects are intrinsic to the nucleotide-ribozyme interaction and not dependent on experimental artifacts.