When it comes to modeling and simulating molecular systems, molecular modelers frequently encounter the need to generate multiple replicas of a structure—whether to explore different configurations in a box or analyze systems containing multiple copies of a protein. But how can you efficiently create and organize these replicas? With SAMSON, a molecular design platform, the process is straightforward, and this guide will walk you through it.
Why Create Replicas?
For molecular dynamics simulations or coarse-grained modeling, replicating structures can save time by minimizing manual input and positioning errors. Whether you are designing a solvated system or building a model with periodic boundary conditions, accurately placed replicas ensure smoother simulations. However, ensuring unique naming and residue numbering for these replicas is critical to avoid issues down the line, such as mislabeled residues or topology generation errors.
Step-by-Step: Creating Replicas in SAMSON
Here’s how you can create replicas manually in SAMSON and ensure they are ready for further use:
1. Ensure All Atoms Are Visible
Before duplicating your structure, ensure all atoms are fully visible. You can toggle the structural model’s visibility by unchecking and checking its checkbox in the interface. This ensures complete clarity of what you’re working with.
The result should display the entire atomic structure of the model:
2. Copy and Paste the Selected Chain
Select the chain(s) you want to replicate. Press Ctrl/Cmd+C to copy the chain and then Ctrl/Cmd+V to paste it. This creates an exact copy of the chain in the same position.
3. Move the Replica
To place the new replica, switch to one of the move editors in the editor toolbar, like the global move editor (shortcut: K). You can now position the chain manually, ensuring clarity and spacing between replicas.
Tip: Use the snapping feature found in the top-left corner of the viewport to set translational or rotational snapping while moving objects.
4. Duplicate More Replicas
Repeat the copy-paste and move steps until you have the desired number of replicas. You can also copy and move multiple chains simultaneously for faster setup.
5. Organize Chains and Residues: Renumber and Rename
After generating replicas, ensure that all residue and chain identifiers are unique. This step is essential for compatibility with downstream workflows such as topology generation. Here’s how:
- Renumber Residues: Right-click the structural model and select Structural model > Renumber residues and structural groups. In the dialog box, start numbering from 1.
- Renumber Chains: Similarly, right-click and choose Structural model > Renumber chain IDs. Leave the default start value as 0.
- Rename Chains: Rename chains for better identification, either by right-clicking in the document or using the Inspector tool.
Concluding the Process
Once you’ve created and organized your replicas, save the system into a file to preserve your work. The replicas are now ready to be used in workflows such as coarse-grained modeling with Martinize2, allowing efficient simulations and structure analysis.
For more details about creating coarse-grained models and building replicas, visit the complete documentation page: https://documentation.samson-connect.net/tutorials/martinize2/martinize2/.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get started with SAMSON at https://www.samson-connect.net.