Molecular modelers often struggle with understanding how proteins transition between conformations. These transitions are vital to understanding protein function, yet analyzing them can involve complex calculations and tools. Fortunately, SAMSON’s Protein Path Finder provides an intuitive way to compute possible transition paths using robust algorithms and straightforward steps.
In this blog post, we will explore how to set up and run the Protein Path Finder to calculate pathways between two conformations of the same protein. We’ll also show how best to define active regions, configure settings, and interpret results.
Set Up Your Protein Transition Model
The first step involves ensuring that you have a properly prepared input model. SAMSON allows you to import sample models, such as Adenylate Kinase, to learn the workflow. Make sure your system is clean by removing solvent, ions, and alternate residue locations. Missing residues or atoms can be fixed with the PDBFixer extension. Special care should be taken to ensure the protein is ready for simulations.
Keep in mind the need for prepared files: if you’re starting from multiple conformations in different files, you will need to concatenate them into a single PDB file using models, like:
|
1 2 3 4 5 6 7 8 |
MODEL 1 ... ENDMDL MODEL 2 ... ENDMDL END |
Note: The sample file from the tutorial is already pre-prepared and optimized for this purpose.
Select Active Regions with ARAP
An essential step in modeling motion is defining active ARAP atoms. These are the atoms that control the protein’s movement during pathway calculations. From the sample model, you can select alpha-carbon (CA) atoms of key residues, such as GLY 12 and ARG 123, as shown below:
If you want to customize this selection, SAMSON supports the Node Specification Language, enabling precise group or residue-based selections.
Configure the Sampling Box
The sampling box is a tool to restrict the motion of active atoms. By default, the box encompasses both start and goal conformations. Adjusting it can influence the explored motion space. For precise pathways, use a box size of 200 Å along each dimension, ensuring sufficient space for sampling.
Run the Planner and Interpret Results
Once your system and sampling box are set up, configure search parameters, including temperature, iteration limits, and minimization steps. This level of control ensures that the results fit the desired level of accuracy and speed. After starting the planner, monitor important metrics such as elapsed time, nodes generated, and paths uncovered:
Paths found during the search are automatically listed in the Results tab. Key metrics for each path include the minimum and maximum energies, energy barriers, and time cost. For example:
Make the Most of Your Results
You can visualize energy curves for the calculated pathways or even export paths as trajectories. This feature is useful for sharing results or conducting further analyses. Additionally, the P-NEB app allows you to refine these paths further.
The Protein Path Finder resolves key pain points for protein modelers, offering a clear pipeline to compute feasible transition paths and visualize them. If you’re ready to dive in, visit the Protein Path Finder documentation for additional details.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. You can get SAMSON at SAMSON Connect.