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ValidatorDB:Terminology

894 bytes added, 01:13, 3 September 2014
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=Molecule=
'''ValidatorDB''' uses ''molecules'' as an umbrella term for ''ligands and non-standard residues''. Therefore, all properties of ligands and non-standard residues are valid for molecules as well (PDB entry of origin, residue annotation, residue identifier, number of heavy atoms, properties assigned after the validation, etc.). Moreover, a single occurrence of a ligand or non-standard residue is also a ''molecule''. Furthermore, it  It is essential to note that '''ValidatorDB''' contains validation results for all ligands and non-standard residues containing ''7 or more heavy atoms''. These are denoted as ''molecules relevant for validation'', or simply ''molecules''. The reason '''ValidatorDB''' focuses on these types of molecules is that they exhibit high diversity and nontriviality in their structure.
=Model=
The term ''motif'' is used here as a fragment of a biomacromolecule, biomacromolecular complex or ligand, made up of
one or more residues or parts of residues. Specifically, the term ''input motif'' refers to the individual molecule being validated, together with its surroundings (i.e., atoms from neighboring residues, within two bonds of any atom of the validated molecule). Each ''input motif'' in '''ValidatorDB''' is assigned a unique motif identifier based on its PDB entry of origin. On the other hand, the term ''validated motif'' (or ''validated molecule'') refers strictly to the subset of atoms in the ''input motif'' which were successfully mapped to atoms in the ''model''.
 
[[File:VDB manual figures2.png|thumb|right|700px|'''A)''' Scheme of the '''validation procedure''' for the entire PDB; '''B)''' Scheme of the '''validation procedure''' for a sialic acid (''SIA'') molecule in PDB entry ''4jtv''; '''C)''' Typical '''validation results''' for ''SIA'' molecules.]]
=Validation procedure=
Within the '''ValidatorDB''' environment, the term ''validation'' refers to the process of determining whether a molecule is structurally complete and correctly annotated. This means checking if the topology and chirality of each validated molecule correspond to those of the model with the same annotation (3-letter code) as the validated molecule. '''ValidatorDB''' implements the ''validation of annotation'' approach, which consists of several steps. First, for each molecule under investigation, the ''input motif'' is extracted from the respective PDB entry. At the same time, the appropriate ''model'' is retrieved from wwPDB CCD. Then, the ''validated molecule'' (or ''validated motif'') is identified as the subset of atoms common in the ''model'' and the ''input motif''. Subsequently, the ''validated molecule'' is compared against the ''model'', atom by atom. All the validation analyses in '''ValidatorDB''' are based on this comparison of atom properties (presence, chirality, element symbol, PDB name, etc.). Other unusual aspects encountered during validation are reported as processing warnings (e.g., which conformer was validated if several conformers were present). Refer to figure..................
=Validation analyses=
=Validation results=
Each molecule is evaluated depending on how it fares during the validation analyses described above. If no issues are found during the validation analyses, the molecule is marked as having ''complete structure and correct chirality''. Validated molecules exhibiting an error in at least one of the ''Completeness'' analyses are denoted as ''incomplete'', whereas the remaining molecules are reported as ''complete''. If no issues are detected during the ''Chirality'' analyses, the validated molecule is marked as having ''Correct chirality'', whereas the remaining molecules are marked as having ''Wrong chirality''. When issues are found during an ''Advanced'' analysis, a warning is reported: Substitution, Foreign atom, Different naming, Zero RMSD or Alternate conformations. Each type of issue encountered during validation has a specific color code.
Some types of chirality errors do not constitute real issues, but are artifacts of the automated chirality determination procedure. Specifically, an error in planar chirality may just mean that the chiral atom is situated slightly above or below the plane compared to its equivalent in the model from wwPDB CCD. Further, an error in high order chirality often marks the involvement of phosphate O atoms in salt or ester formation, or merely a different PDB format identification of phosphate O atoms of the validated molecule compared to the model. Therefore, if the validated molecule is found to have planar or high order chirality errors, but no other type of chirality issues, the molecule is marked as having ''Correct chirality (tolerant)''.
When issues are found during an ''Advanced'' analysis, a warning is reported: Substitution, Foreign atom, Different naming, Zero RMSD or Alternate conformations. While the results of the ''Advanced'' analyses have no bearing over the chemical soundness of the validated molecules, they indicate that further, especially automated processing of these structures can be very problematic. Comparison between the structures of molecules with the same annotation (3-letter code) from different PDB entries might even be impossible in the presence of a substitution, as the corresponding atoms have different chemical elements. PDB atom names cannot be used straightforwardly, since even element symbols can differ and atoms can be formally included in neighboring residues.
=Validation reports=
In For each PDB entry, the relevant molecules are detected and validated. '''ValidatorDB''', is then built as the results collection of the validation analyses results for all molecules in all PDB entries. The results are systematically organized systematicallyinto reports:* Validation overview for the entire PDB: summarizes the results of all validation analyses for all molecules
* Summary of validation results for sets of molecules sharing the same annotation
* Summary of validation results for sets of molecules originating from the same PDB entry

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