Dear All, It's been a couple of weeks since Greg first helped me with this, and after some further help I agreed that I would do my best to summarise things for the benefit of the Group. The attached file 'sanifix3.py' was provided to me by Greg, and essentially does exactly what I (thought I) wanted - ie if required, 'cleans' up an input molecule by modifying aromatic nitrogen-containing ring systems until a 'sanitizable' form is generated. However, having tested this a bit further, I found that N-containing heteroaromatics (which I originally posted the question about) are only one of many possible issues when dealing with automated atom- and bond-typing from PDB files! So taking this approach would require a significantly larger set of 'rules' to cover all possible problems (I'm sure many people more experienced than me will have been aware of this for a long time!). As Greg said: > Figuring out the correct chemistry for a pdb ligand is one of > those challenges at I wouldn't dream of attempting. Between > the various sources of ligand structures out there you can > probably find omsething at least halfway acceptable. For in > house stuff, I would assume that you can use the registry > number to get a smiles or mol block, right? > You could use that with the rdkit substructure matching code > to test the pymol-assigned structures.
And indeed, this is the way that I ended-up going for in-house structures - a script that extracts our corporate ID from the PDB file and searches our database to return the SMILES. Then (again, thanks to Greg for more help here, and steering me away from some clumsy usage of ConstrainedEmbed!) a substructure match is conducted between an RDKit mol from the SMILES (refered to as 'db_mol' in the function below), and the original ligand. The main point here is to convert the original ligand structure to a set of non-aromatic atoms joined by 'unspecified' bond-types. Below is the excerpt from what I am using with PyMOL: 'molfile3D' is a temporary molfile that has been created using the PyMOL 'save' command, that gets converted to the required 'connectivity substructure' that carries the 3D coordinates we will need later: def make3DTemplate(molfile3D): mol = Chem.MolFromMolFile(molfile3D, False) for atom in mol.GetAtoms(): atom.SetIsAromatic(False) for bond in mol.GetBonds(): bond.SetBondType(rdkit.Chem.rdchem.BondType.UNSPECIFIED) return mol Then once we have this '3D template', the substructure match can be conducted for the molecule built from the database SMILES string (db_mol). If the match is successful, the original 3D coordinates for the atoms in the 'template' are then applied back to a conformer of our new molecule. Finally, this new molecule + conformation is returned as the molblock, which I then read back in PyMOL to give a 'sanitized' version of the bound ligand for any in-house crystal structure: def outputMolBlock(db_mol, template_mol): matches = db_mol.GetSubstructMatches(template_mol) if not matches: raise ValueError,"no substruct match" if len(matches)>1: print "warning! more than one isomorphism found!" db_conf = db_mol.GetConformer() template_conf = template_mol.GetConformer() match = matches # This sets the 3D coordinates for for i,mIdx in enumerate(match): db_conf.SetAtomPosition(mIdx, template_conf.GetAtomPosition(i)) db_conf.Set3D(True) return Chem.MolToMolBlock(db_mol) It wouldn't now be too much of a leap(?) to extend the same methodology to public PDB structures - using the LigandExpo SDF. See this post from Noel on Blue Obelisk for background: http://blueobelisk.shapado.com/questions/how-to-get-an-experimental-liga nd-structure-from-the-pdb Also, just for interest - I am using cx_Oracle to connect to our corporate database from Python, which is now allowing me to add a few extra bits - like flagging up to people if the in-house structure they have just opened has been previously crystallised in any other targets, etc, etc. If anybody is trying to do similar, but has not used cx_Oracle, then give me a shout and I will see if I can help (although SQL is definitely also on the list of things I know only barely enough about!). Kind regards James ______________________________________________________________________ PLEASE READ: This email is confidential and may be privileged. It is intended for the named addressee(s) only and access to it by anyone else is unauthorised. If you are not an addressee, any disclosure or copying of the contents of this email or any action taken (or not taken) in reliance on it is unauthorised and may be unlawful. If you have received this email in error, please notify the sender or postmas...@vernalis.com. Email is not a secure method of communication and the Company cannot accept responsibility for the accuracy or completeness of this message or any attachment(s). Please check this email for virus infection for which the Company accepts no responsibility. If verification of this email is sought then please request a hard copy. Unless otherwise stated, any views or opinions presented are solely those of the author and do not represent those of the Company. The Vernalis Group of Companies Oakdene Court 613 Reading Road Winnersh, Berkshire RG41 5UA. Tel: +44 118 977 3133 To access trading company registration and address details, please go to the Vernalis website at www.vernalis.com and click on the "Company address and registration details" link at the bottom of the page.. ______________________________________________________________________
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