# How do metal ions direct ribozyme folding?

## TL;DR

This study shows how metal ions like Mg2+ help ribozymes fold properly and become active, while other ions like Ca2+ can cause incomplete activation.

## Contribution

The study reveals how Mg2+ ions specifically stabilize ribozyme structure and active site, while Ca2+ cannot.

## Key findings

- Group I ribozymes form structural elements spontaneously at low Mg2+ concentrations.
- Higher Mg2+ concentrations are needed for full ribozyme folding and active site stabilization.
- Ca2+ ions allow folding but fail to stabilize the active site for catalytic activity.

## Abstract

Ribozymes, which carry out phosphoryl transfer reactions, often require Mg2+ ions for catalytic activity. The correct folding of the active site and ribozyme tertiary structure is also regulated by metal ions in a manner which is not fully understood. Here, we employ coarse-grained molecular simulations to show that individual structural elements of the group I ribozyme from the bacterium Azoarcus form spontaneously in the unfolded ribozyme even at very low Mg2+ concentrations, and are transiently stabilized by coordination of Mg2+ ions to specific nucleotides. However, competition for scarce Mg2+ and topological constraints arising from chain connectivity prevent complete folding of the ribozyme. A much higher Mg2+ concentration is required for complete folding of the ribozyme and stabilization of the active site. When Mg2+ is replaced by Ca2+ the ribozyme folds but the active site remains unstable. Our results suggest that group I ribozymes utilize the same interactions with specific metal ligands for both structural stability and chemical activity.