On Thu, May 14, 2009 at 03:03:57PM -0400, Guangyu Zhu wrote:
> Zn and Se have similar f' and f''. Why Zn seems have much better phasing
> powder in practice? Is it just because Zn always binds tightly on protein
> but Se might have higher b-factor?
Also: Met sidechains often adopt alternate conformations (that still
occupy the same space). You can see that in any structure, not only
Se-MET (but also S-Met).
If these alternate conformations are distinct enough, one can
obviously model the minor conformations as well (e.g. by checking the
LLG maps from SHARP). But the HA detection often finds only the main
position - or the user restricts the sites to the maximum expected one
according to sequence.
Not sure though if that has as big an effect on the Zn/Se difference
as the tightness/B-factor argument.
Clemens
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