MolProbity_3D

MolProbity_3D validates macromolecular models by analyzing geometry, steric clashes, rotamers, Ramachandran statistics, water assignments, and peptide orientations to diagnose and improve structural accuracy for X-ray crystallography and cryo-EM-derived models.

Key Features:

• CCTBX integration: Core validation routines are powered by the Computational Crystallography Toolbox (CCTBX) for crystallographic calculations and checks.
• PDB format compliance: Emphasizes strict adherence to PDB file format standards during validation.
• Geometry and clash analysis: Quantifies bond/angle geometry, steric clashes, and related outliers.
• Rotamer and Ramachandran assessment: Evaluates side-chain rotamers and backbone Ramachandran statistics to flag conformational outliers.
• UnDowser (HOH analysis): Analyzes clashing HOH "waters" and provides diagnostic scenarios to distinguish genuine waters from misassigned entities.
• CaBLAM peptide-orientation analysis: Diagnoses local peptide-orientation errors especially at lower resolutions typical of 3–4 Å cryo-EM data.
• Alternate-conformation handling: Expands validation for alternate conformers to ensure thorough local assessment.
• Neo4j graph database: Uses a Neo4j graph database to support larger, cleaner reference datasets for model assessment.

Scientific Applications:

• Macromolecular model validation: Detects and quantifies geometry, clash, rotamer, and Ramachandran outliers in protein and nucleic acid models.
• Water assignment diagnostics: Identifies and classifies clashing HOH "waters" to aid in distinguishing true solvent from misassigned atoms.
• Low-resolution cryo-EM validation: Applies CaBLAM to reveal peptide-orientation errors and local misassignments in 3–4 Å cryo-EM maps.
• Alternate-conformation evaluation: Validates and audits alternate conformers to improve local model reliability.
• Reference-set-based assessment: Leverages larger reference datasets stored in Neo4j for more robust comparative validation and benchmarking.

Methodology:

Implements CCTBX-based validation routines with strict PDB format checks, stores reference data in a Neo4j graph database, performs UnDowser analysis of clashing HOH waters, applies CaBLAM peptide-orientation analysis, and includes expanded alternate-conformation validation.