Hi Andy,
I'd say fairly common, and there can be several reasons. One is that the
entrance of the active site (in case of crystal soaks) is blocked in
some subunits. Also, different affinities in the different active sites,
plus allosteric effects, are possibilities to consider.
The latest example here I can give you (unpublished yet) is a mutant of
an NAD-binding tetrameric enzyme. The crystals were grown by
co-crystallisation. Out of the 4 active sites, only 2 of them contain
cofactor plus substrate analogue.
It is likely that the scientists who do large scale analyses of the PDB
using automated programs have done a systematic search in the PDB and
could provide you with accurate statistics. I wouldn't know any
reference to such work (I am not in that field myself).
Fred.
ANDY DODDS wrote:
Hello,
I am solving a structure of an enzyme, which crystallises as a dimer.
We have pretty good evidence that this operates as a dimer in vitro,
also. We have an inhibitor of this enzyme, which we are keen to
visualise by X-ray methods.
We seem to have very strong density in which we can model our
inhibitor, with good stats and no negative density. However, there is
only density in one of the monomers, nothing in the other. The SG is
P212121, and although I can postulate why this may have happened (if
this is indeed what HAS happened), different solvent channel
accessibility etc., I would like to know how common this was and, if
possible, some literature regarding this, if the board would be so
kind?
Regards,
Andrew.
