Servers for ligand topologies/parameters
How to generate topology/parameter files for unknown ligand[edit | edit source]
CCP4 AceDRG () needs to be fed the SMILES string of your compound, and it returns the CIF file. Many compounds are actually already in the CCP4 dictionary. Finding out whether a compound is, is a two-step procedure:
- Go to http://ligand-expo.rcsb.org/ and use the search option to find out whether the compound is already in the PDB
- If it is, you now have a residue name. To check whether the compound is also in the CCP4 dictionary, just use the 'Get monomer' option in Coot.
Within coot, you can
- use Lidia to make a chemical diagram, press "Apply" to run Acedrg
- or use Lidia to determine the SMILES string and use the "Make a Ligand" task in CCP4i2
You also might want to check the HIC-Up website, and the NCBI Pubchem database at http://pubchem.ncbi.nlm.nih.gov/. The sdf file can be downloaded and converted to PDB format.
Another solution to this problem is the Dundee PRODRG server. It is self-explanatory (you define the ligand structure by providing coordinates in PDB format, drawing molecule using JME editor, etc.) and produces coordinates and topology/parameter descriptions in the following formats:
- MDL Molfile
One inconvenience is that PRODRG server always names your new residue DRG and gives atoms some funny names (CAA, CAX, etc.). If you prefer to control the naming system, take the PDB output, rename residue/atoms to your liking and rerun it.
base pairing and base stacking[edit | edit source]
- PDB coordinates to Restraints - This Web-server generates custom RNA/DNA base stacking and base pairing restraints for crystallographic refinement. Input is in PDB format. Output is Pymol , CNS and PHENIX formatted.