Coordinates accuracy

[Lynn F. Ten Eyck]

Vincent Escalier wrote:
> 
> Hello,
> 
>  I'd like to have a measure of accuracy of the coordinates in a PDB
> file. I need a quantitative measure, and resolution doesn't make it.
> I would need something like 'the x-coordinate of atom #1234 is
> equal to 0.2345 +- 0.05 A '. Is it possible to have such an
> information ?

Unfortunately this information requires a full matrix least squares
analysis.  Some of the possibilities are given in a paper I presented
at the January 1996 CCP4 Study Weekend; the situation is complicated
by the fact that the normal matrices are frequently singular for
macromolecules, but this is only a complication, not a real barrier.

Bottom line: it is not current practice.  If you specifically need the
information for a case in which you have structure factors, you have
some hope.

Lynn Ten Eyck
San Diego Supercomputer Center