A fast and robust torsion bond analyser has been created for the analysis of torsion strain in small molecules bound to proteins.
DesertSci software uses SMARTS based ligand atom matching and a hierarchical dataset of expected torsion angles based on experimental structures .
Atoms are coloured according to torsion violations, with green indicating that a torsion angle is within expected values, orange means borderline, and red atoms indicate the possibility of an unfavourable torsion – where the angle is outside of the expected range.
Proasis4 has been extended so that ligand atoms associated with torsion angles are colour-coded with the ‘Property’ torsion_flags, highlighting the favourable and unfavourable torsion angles.
The torsion flags provide insight into where a protein binding site is enforcing an unfavourable conformational change into a small molecule, thereby enabling other ligand designs/ligand modifications to be considered.
ProasisAPI has been extended to include a torsion analysis tool, enabling the identification of favourable and unfavourable torsion angles in any any protein-ligand complex in Proasis, or any pdb file on the local file system.
 Schärfer, C., Schulz-Gasch, T., Ehrlich, H.C., Guba, W., Rarey, M., Stahl, M. (2013). Torsion Angle Preferences in Drug-like Chemical Space: A Comprehensive Guide. Journal of Medicinal Chemistry, 56 (6):2016-28.