[ccp4bb]: Comments on ligands

[Phil Evans <pre@mrc-lmb.cam.ac.uk>]

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I don't think any of the current stereochemical dictionaries are
reliable enough to accept without checking. They're probably OK for
common ligands (amino acids, nucleotides) but anything else needs
checking: the CSD database is very helpful in many cases, but not
always. 

Certainly the refmac dictionaries have some doubtful things in them:
don't accept anything that says it comes from a minimal description

I believe the HICUP collection at Uppsala is just abstracted from the
PDB (is this true?) which is thus open to propagating errors (there's
at least one CoA in the PDB with a wrong chirality for instance).

Until a more general checking is properly implemented, caveat emptor.
There is definitely a need for better tools, though things have
improved over the last few years.

On the question of depositing structure factors, this should be
compulsory (why isn't it?). There is no excuse for not depositing
them, and the most likely person to want them is you yourself.

Phil