When modeling molecules, the ability to target specific subsets of atoms, residues, or molecules within a structure—while applying filters and criteria—is an invaluable skill. For instance, how do you quickly identify atoms in contact with a ligand, residues coordinating metals, or potential salt-bridge candidates? Fortunately, SAMSON’s NSL simplifies this process with its structured syntax for molecular selections.
If you’ve struggled with efficiently filtering and analyzing molecular data, this guide walks you through how NSL can address common modeling challenges. Here are some practical examples for you to apply in your molecular studies:
Key Examples of NSL Selections
Below, we address specific molecular modeling questions and their solutions using NSL. Each case is designed for real-life tasks—perfect for improving your workflows.
1. Identifying Ligand Contact Points
Want to find receptor residues located within 6Å from any ligand, excluding small residues like Glycine (GLY) or Alanine (ALA)? This is particularly helpful for mutagenesis studies.
NSL query:
((n.t r and not r.t GLY,ALA) in n.c rec) w 6A of n.c lig
2. Pinpointing Backbone Hydrogen Bond Donors
For tasks requiring analysis of precise ligand-protein interactions, you might need to locate backbone nitrogen atoms (N) that contact a ligand within 3Å.
NSL query:
(a.s N in n.t bb) w 3A of n.c lig
3. Highlighting Polar Active Sites
To analyze polar contributions to ligand binding within 3Å of the receptor’s heavy atoms (Oxygen or Nitrogen):
NSL query:
(a.s O,N in n.c rec) w 3A of n.c lig
4. Identifying Disulfide Interactions
Searching for sulfur atoms specifically involved in disulfide (S-S) bridges near ligand atoms within a 5Å radius can be crucial for analyzing stabilizing interactions:
NSL query:
((a.s S in r.t CYS) l (a.s S in r.t CYS)) w 5A of n.c lig
5. Pathways to Major Structural Insights
You can use NSL to track down residues near glycans (sugars) or water molecules that bridge ligand-receptor surfaces. For example, if you need to locate waters that are 3.2Å from chains “A” and “B” simultaneously:
NSL query:
(n.c wat w 3.2A of c.n "A") and (n.c wat w 3.2A of c.n "B")
6. Simplifying Geometry-Based Selections
For specific geometry-related filters such as identifying atoms with x >= 2y near ligands:
NSL query:
(a.x >= 2*a.y) and (n.t a w 4A of n.c lig)
Why This Matters
Such queries are essential because they allow researchers to rapidly specify atom-, residue-, or chain-level subsets within molecular assemblies. Instead of manually inspecting structures or using complicated scripts, NSL streamlines selection tasks in a readable and replicable way.
The provided examples are just scratching the surface. With NSL, you can construct highly sophisticated queries for diverse modeling tasks. For detailed explanations and a complete list of selection types, refer to the original documentation page linked below.
Learn more about NSL examples in the documentation here.
SAMSON and all SAMSON Extensions are free for non-commercial use. You can download it at samson-connect.net.