Henry Gabb wrote in response two my posting:
> Just out of curiosity, why do you want to distinguish between ... (the
> two phosphate oxygens OP1 and OP2) ?
Because I want to calculate true rms distances between a crystral
structure form the Brookhaven database and a modell. I have tried
this for the drew-dickerson dodecamer '1BNA' using InsightII.
In the structure build with Insight the two phosphate oxygens are
pointing just to the opposite direction as in the crystal structure.
If I now calculate the rms distance between the two structures I
get a wrong value because the atoms in the two structures are
aligned according to their ordering in the pdb files and _not_
according to their chiral positions.
>> The structural meaning of this would be, whether OP1 is pointing towards
>> the minor or the major groove in a DNA double helix.
> That suggestion works fine for a static structure. Since the backbone
> torsions are flexible, the positions of the phosphate oxygens and C5'
> hydrogens with respect to the grooves can reverse.
> ...
> It's easy to draw a distinction between the H2' and H2'' atoms of the
> sugar; one will always be above the ring (i.e., on the same side as the
> C5') and one will always be below.
No, OP1 and OP2 will never reverse since P is a prochiral center and since the
position of P is fixed through O3' and O5'. With OP1 and OP2 it is
exactly the same kid of problem as with H2'1 and H2'2, but for H2'1/H2'2
and H5'1/H5'2 the correct positions are defined by the IUPAC
recommendation of 1982 (IUPAC. 1983. Europ J Biochem, 131: 9-15.).
Therefore my question is, if there exist any recommendation for the
phoshate oxygens.
Peter
---
Peter Slickers slickers at imb-jena.de
Institut fuer Molekulare Biotechnologie
Beutenbergstrasse 11, Jena Tel.: +49-3641-65-6202
Postfach 10 08 13, D-07708 Jena, Germany Fax: +49-3641-65-6210
