# ARIP: A Tool for Precise Interatomic Contact Area and Volume Calculation in Proteins

## TL;DR

ARIP is a new tool that calculates interatomic contact areas and volumes in proteins to better understand their structure and function.

## Contribution

ARIP introduces a modified algorithm for precise contact area and volume calculation using van der Waals radii and solvent parameters.

## Key findings

- ARIP uses a modified dr_sasa algorithm and atomic overlap weighted method for contact calculations.
- The tool can analyze multiple models in a single PDB file, suitable for molecular dynamics.
- ARIP was successfully applied to four cases including protein-drug and protein-DNA interactions.

## Abstract

The interplay patterns of amino acid residues are pivotal in determining the tertiary structure and flexibility of proteins, which in turn are intricately linked to their functionality and interactions with other molecules. Here, we introduce ARIP, a novel tool designed to identify contact residues within proteins. ARIP employs a modified version of the dr_sasa algorithm and an atomic overlap weighted algorithm to directly calculate the contact area and volume between atoms based on their van der Waals radius. It also allows for the selection of solvent radii, recognizing that not every atom in proteins can interact with water molecules. The solvent parameters were derived from the analysis of approximately 5000 protein and nucleic acid structures with water molecules determined using X-ray crystallography. One advantage of the modified algorithm is its capability to analyze multiple models within a single PDB file, making it suitable for molecular dynamic capture. The contact volume is symmetrically distributed between the interacting atoms, providing more informative results than contact area for the analysis of intra- and intermolecular interactions and the development of scoring functions. Furthermore, ARIP has been applied to four distinct cases: capturing key residue–residue contacts in NMR structures of P4HB, protein–drug binding of CYP17A1, protein–DNA binding of SPI1, and molecular dynamic simulations of BRD4.