I've been reading the contributions on this topic with much interest.
It's been very timely in that I've been giving 3rd year u/g lectures
on protein X-ray structures and their validation over the past week.
As part of the preparation for the lectures, I searched the PDB for
structures with high solvent content.
To my surprise, I found 376 crystal structures with solvent content
>75% (about 1% of all crystal structures) and 120 structures with
solvent content > 80% (about 0.3% of all crystal structures)
However, there were only 3 other structures that (like 2HR0) had >80%
AND Rcryst Rfree less than 20%. All three structures are solved to
better than 3A Resolution.
One is from a weak data set from a virus crystal, the other two PDB
files report very strong crystallographic data.
The Rmerge values are more typical than for 2HR0 and none of the
three appear to have the geometry or crystal contact problems of 2HR0.
My question is, how could crystals with 80% or more solvent diffract
so well? The best of the three is 1.9A resolution with I/sigI 48 (top
shell 2.5). My experience is that such crystals diffract very weakly.
There are another 15 structures with solvent content 75-80% and
Rcryst/Rfree < 20%. I didn't check them in any detail, just to see
that the structure was consistent with a high solvent content.
Any thoughts?
Cheers,
Jenny
