One of the common challenges molecular modelers encounter is the need to simulate systems with multiple replicas of the same protein. Whether preparing coarse-grained models or evaluating different molecular dynamics setups, managing replicas efficiently is key to saving time and avoiding errors. In this guide, we explore how to create and manage replicas manually in the SAMSON platform, ensuring that your systems are ready for seamless topology generation and simulations.
Why Replicas Matter
Replicas allow researchers to study multiple instances of the same molecule under varied conditions or in different orientations within complex assemblies. However, crafting such systems can be tedious if residue and chain IDs overlap or if replicas aren’t easily identifiable. Manual preparation ensures a clean, organized setup, avoiding downstream topology generation issues.
Step-by-Step: Creating Protein Replicas Manually
The manual method provides full control over the process. Here’s how you can do it:
Step 1: Make Atoms Visible
Before creating replicas, ensure that all atoms are visible in your structure to prevent missing any part of the system. Toggle visibility by unchecking and rechecking the structural model’s checkbox. This way, you’ll have a clear view of the molecule.
This should result in a fully visible atomic structure, like the example shown below:
Step 2: Copy Chains
Next, select the chain(s) you want to replicate. With the chain selected, press Ctrl/Cmd + C to copy and Ctrl/Cmd + V to paste. The new chain will appear at the same position as the original.
Step 3: Move Replicas
While the pasted chain is still selected, use one of the move editors (shortcut: K) to position the replica as needed. Adjust translational or rotational snapping in the top-left corner of the viewport, if necessary, to ensure precision.
Repeat this process to create as many replicas as required. Pro-tip: You can select and move multiple chains simultaneously for efficiency.
Ensuring Unique Residue and Chain IDs
Once replicas are created, it’s crucial to renumber residue and chain IDs to avoid potential issues during topology generation:
- Renumber Residues: Right-click on the structural model and select Structural model > Renumber residues and structural groups. In the pop-up dialog, leave the value as 1 and click OK.
- Renumber Chains: Right-click on the structural model and select Structural model > Renumber chain IDs. Leave the default value as 0 in the dialog and confirm.
- Rename Chains: Chains can be renamed directly in the document or via the Inspector. Use
F2or the context menu for efficient renaming.
Save and Proceed
Once your replicas are created and numbered uniquely, save the system to a file to preserve your work. You’re now ready to use these replicas for coarse-grained modeling, as described in the next steps for topology generation.
Learn More
If you’re ready to dive deeper, refer to the complete Martinize2 tutorial for comprehensive guidance on creating coarse-grained models within SAMSON’s environment.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get started with SAMSON at https://www.samson-connect.net.