Re: [ccp4bb]: Can I find a zinc in a haystack?

["Diana R. Tomchick" <drt7f@unix.mail.virginia.edu>]

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On Wed, 24 May 2000, Jeff Taylor wrote:

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> 
> Hi -
> 
> I have crystals of a 90KD protein that has a single zinc site.  Although
> I have what should be a good model for molecular replacement, I haven't
> been able to solve it.  I'm planning to try and substitute a Hg for the
> Zinc in hopes of using the anomalous signal to determine the location of
> the metal site (and there by solving the translation portion of the
> molecular replacement).  Does this sound reasonable?
> 
> The Hg substitution may be difficult in this case, so I'm also wondering
> if there is any possibility that I might be able to do the same thing
> using the absorption edge of the zinc?  
> 
> I don't have much experience in these matters.  Would this simply be too
> small a signal for this large of a protein?
> 
> All opinions are appreciated.  Thank you,
> 
> Jeff Taylor
> 

Depends upon the quality of the crystal and your data quality and 
redundancy. We are able to easily measure anomalous differences at the
Fe K-edge for a protein of similar size (soybean L-1 lipoxygenase, 94 kDa,
typical diffraction to 1.6 angstroms), so I wouldn't hesitate to try.

Diana

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

  Diana R. Tomchick
  Department of Molecular Physiology and Biological Physics
  Rm. 4223, Jordan Hall
  University of Virginia
  1300 Jefferson Park Avenue
  Charlottesville, VA 22908
  (804)924-2948
  (804)982-1616 (fax)
  drt7f@virginia.edu
  www.people.virginia.edu/~drt7f