# Treatment of flexibility of protein backbone in simulations of protein–ligand interactions using steered molecular dynamics

## TL;DR

This paper explores how to simulate protein-ligand interactions by adjusting how much the protein backbone is restrained during simulations.

## Contribution

The study proposes a novel restraint strategy using Cα atoms at a specific distance from the ligand to improve simulation accuracy.

## Key findings

- Fixing all heavy atoms or Cα atoms is not effective for simulating ligand release.
- Restraining only distant Cα atoms leads to more natural ligand release.
- Too few restrained atoms can cause the protein to rotate and collide with the active site.

## Abstract

To ensure that an external force can break the interaction between a protein and a ligand, the steered molecular dynamics simulation requires a harmonic restrained potential applied to the protein backbone. A usual practice is that all or a certain number of protein’s heavy atoms or Cα atoms are fixed, being restrained by a small force. This present study reveals that while fixing both either all heavy atoms and or all Cα atoms is not a good approach, while fixing a too small number of few atoms sometimes cannot prevent the protein from rotating under the influence of the bulk water layer, and the pulled molecule may smack into the wall of the active site. We found that restraining the Cα atoms under certain conditions is more relevant. Thus, we would propose an alternative solution in which only the Cα atoms of the protein at a distance larger than 1.2 nm from the ligand are restrained. A more flexible, but not too flexible, protein will be expected to lead to a more natural release of the ligand.