When working on molecular models, you often face the challenge of refining specific parts of a molecule without disrupting the rest. This is particularly important when your structure is complex and only a small region needs adjustment. In SAMSON, this problem is addressed through a straightforward and interactive process called “partial minimization”—and here’s how you can take advantage of this.
Why Minimize a Part of a Molecule?
Imagine working on a macromolecule where only a specific site (such as an active site of a protein-ligand system) needs optimization. Running a full molecular minimization may not only be computationally expensive but can also disrupt other regions of the molecule that you want to keep unchanged. Partial minimization allows you to focus on specific parts while freezing the rest of the structure.
How to Minimize a Part of a Molecule
SAMSON provides a step-by-step approach to minimize only parts of a molecule. Follow these instructions to get started:
- Select the entire molecule or leave the selection empty if you wish to start with a broader scope.
- Navigate to Edit > Freeze. This freezes the atoms in your selection or, if nothing is selected, freezes the entire molecule.
- Select the part of the molecule that you want to minimize.
- Go to Edit > Unfreeze to unfreeze only the selected atoms.
- Start the minimization process by clicking Edit > Minimize. During this step, SAMSON interactively minimizes the selected atoms while keeping the frozen components fixed.
- After achieving the desired minimization, click Edit > Minimize again to stop the process.
- Once finished, unfreeze the entire system by using Edit > Unfreeze with either the molecule selected or no selection at all.
During this workflow, any frozen (fixed) atoms appear with a dark blue overlay in SAMSON’s viewport, making it easy to visually identify which parts of the molecule are immobilized.
An Example in Action
Partial minimization isn’t just theoretical—it is also visually intuitive. This feature allows you to work on specific regions without impacting the molecule as a whole. For example, you might minimize a loop in a protein structure while ensuring neighboring residues and domains remain fixed.
The interactive control built into SAMSON gives you immediate feedback, so you always remain in control of what is being refined versus what stays as is.
Freezing and Unfreezing: Practical Tips
If at any point you’re unsure about which atoms are frozen, they are visually indicated with a dark blue color in the viewport. This visual cue ensures that you don’t accidentally minimize frozen regions or modify regions that should stay fixed.
Once your minimization is complete, remember to unfreeze the molecule to return to a fully interactive model. This step ensures you’re ready for further modifications or analyses.
Learn More
SAMSON’s approach to partial minimization is an incredibly useful feature for molecular modelers who want precision without compromise. To explore this feature in even greater detail, visit the full minimization documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Download SAMSON now at https://www.samson-connect.net.