Unlocking the Power of Residue Attributes in Molecular Modeling

Molecular modelers often need to filter, select, or analyze specific residues based on structural or functional properties. Effectively working with residue attributes can dramatically boost modeling efficiency and accuracy. This blog post introduces SAMSON’s residue attributes in the Node Specification Language (NSL), providing an overview of their capabilities and a guide to their usage.

What Are Residue Attributes?

Residue attributes in SAMSON’s NSL help modelers specify and match residues based on diverse properties. These could include physical characteristics, structural roles, or chemical information. Attributes are organized under the residue attribute space (short names: res, r), making them convenient for complex queries.

For example, with residue attributes, you can identify amino acids with specific charges, detect residues visible in different model states, or target nucleic acids.

Categories of Residue Attributes

Residue attributes are grouped into several categories, inheriting characteristics from more general attribute spaces like node and structuralGroup. Below are a few highlights:

General Attributes

Residues inherit basic attributes like visibility and selection from the node space. Examples include:

  • r.v (visible): Filters for residues that are visible (true or false).
  • not r.h (hidden): Identifies residues that are not hidden.

Structural Insights

The structuralGroup space provides structural properties:

  • r.nat < 100: Finds residues with fewer than 100 atoms.
  • r.nC 10:20: Matches residues with carbon atom counts between 10 and 20.

Advanced Biochemical Filtering

Residue attributes specific to residue space enable powerful biochemical filtering:

  • r.ss helix: Matches residues in alpha helices.
  • r.c pos: Identifies residues with positively charged side chains.
  • r.aa: Detects amino acid residues (true or false).
  • r.daa: Focuses explicitly on D-amino acids.

Residue-Specific Properties

Some attributes depend solely on residue types. Examples include:

  • r.hydrophobicity < 0: Filters for residues with negative hydrophobicity values (based on the Kyte-Doolittle scale).
  • r.p neutral: Matches residues with neutral polarity.
  • r.pKa1 < 2.0: Filters residues with a dissociation constant (pKa1) below 2.0.

Applications in Real-World Molecular Modeling

Here are some use cases where residue attributes can come to the rescue:

1. Identifying Key Residues in a Protein

To focus on alpha helices in a protein:

This will match residues that contribute to alpha-helical structures.

2. Filtering Charged Residues

To isolate residues with positive or neutral charges:

This can help analyze interactions within active sites or binding pockets.

3. Pinpointing Specific Atom Types

Want to find alpha carbons in alanines?

This matches the alpha-carbon atoms in all alanine residues, ideal for focused geometric analyses.

Getting Started

Residue attributes offer granular control over molecular data. By leveraging the short names, you can efficiently tailor queries for your workflow. SAMSON’s NSL documentation provides further details on individual attributes and their potential combinations.

To explore the full list of residue attributes and examples, visit the official documentation at: https://documentation.samson-connect.net/users/latest/nsl/residue/

SAMSON and all SAMSON Extensions are free for non-commercial use. You can download SAMSON at https://www.samson-connect.net.

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