Threshold occupancy and specific cation binding modes in the hammerhead ribozyme active site are required for active...

Area of Science:

• Biochemistry
• Molecular Biology
• Computational Chemistry

Background:

• Hammerhead ribozyme (HHR) is a catalytic RNA molecule essential for various biological processes.
• Metal ions, particularly Mg2+, are known to be critical for HHR activity, but their precise roles are still debated.
• Understanding the interaction between metal ions and HHR structure is key to elucidating its catalytic mechanism.

Purpose of the Study:

• To investigate the relationship between metal ion binding (Na+ and Mg2+) and the formation of catalytically active conformations in HHR.
• To explore the role of metal ion concentration and coordination in stabilizing HHR structures.
• To reconcile experimental findings on HHR metal ion sensitivity with molecular dynamics simulations.

Main Methods:

• Molecular dynamics (MD) simulations were employed to model HHR in the presence and absence of different metal ions.
• Analysis focused on the occupancy and coordination patterns of Na+ and Mg2+ ions.
• The simulations examined the stabilization of negatively charged groups and the formation of active in-line attack conformations.

Main Results:

• Different metal ion occupancy thresholds were required to stabilize repulsive interactions in reactant and activated states.
• Specific bridging coordination patterns of metal ions were correlated with the formation of active conformations.
• HHR was observed to fold into an electronegative pocket that recruits high local concentrations of positive charge.

Conclusions:

• Mg2+ plays a significant role in stabilizing the active conformation of HHR.
• The findings suggest that Mg2+ has a specific chemical role in HHR catalysis beyond mere structural stabilization.
• Simulations provide a molecular basis for understanding the metal ion sensitivity of HHR catalysis and reconcile experimental data.