What is Tortoize?

Tortoize checks the torsion angles in your protein model and gives them a Z-score based on their distribution in high quality models in the PDB-REDO databank. Higher Z-scores are better. For each residue, two sets or torsion angles are checked: φ/ψ combinations (the Ramachandran plot) and χ₁/χ₂ combinations(the rotamers). The distributions that are use to check torsion angles are residue en secondary structure (as assigned by DSSP) specific. The strength of Tortoize is that assigns global, per-model Z-scores on top of the per-residue scores (the Ramachandran Z-score, or Rama-Z and the rotamer Z-score). These global scores tell you how normal your Ramachandran plot and your rotamer distribution are compared to high-quality structure models. And, unlike per-residue scores, these global scores are not sensitive to over-enthusiastic use of restraints in model making.

The Tortoize papers and code