On Tuesday, October 30, 2012 01:44:43 pm Adrian Goldman wrote:
> The coordination is indicative but not conclusive but, as I responded to the
> original poster, I think the best approach is to use anomalous scattering.
> You can measure just below and above the Ca edge,
Actually, you can't. The Ca K-edge is at 3.07Å, which is not a wavelength
amenable to macromolecular data collection.
cheers,
Ethan
> and similarly with the Zn, and those maps will be _highly_ indicative of the
> relative amounts of metal ion present. In fact, you can deconvolute so that
> you know the occupancy of the metals at the various sites.
>
> Adrian
>
>
> On 30 Oct 2012, at 22:37, Chittaranjan Das wrote:
>
> > Veerendra,
> >
> > You can rule out if zinc has replaced calcium ions (although I agree with
> > Nat and others that looking at the coordination sphere should give a big
> > clue) by taking a few crystals, washing them a couple of times and
> > subjecting them to ICP-MS analysis, if you have access to this technique.
> > You can learn how many zinc, if any, have bound per one protein molecule in
> > the dissolved crystal.
> >
> > Best
> > Chitta
> >
> >
> >
> > ----- Original Message -----
> > From: "Veerendra Kumar" <[email protected]>
> > To: [email protected]
> > Sent: Tuesday, October 30, 2012 2:55:33 PM
> > Subject: [ccp4bb] Ca or Zn
> >
> > Dear CCP4bb users,
> >
> > I am working on a Ca2+ binding protein. it has 4-5 ca2+ binding sites. I
> > purified the protein in presence of Ca2+ and crystallized the Ca2+ bound
> > protein. I got crystal and solved the structure by SAD phasing at 2.1A
> > resolution. I can see the clear density in the difference map for metals at
> > the expected binding sites. However I had ZnCl2 in the crystallization
> > conditions. Now i am not sure whether the observed density is for Ca or Zn
> > or how many of them are ca or zn? Since Ca (20 elctron) and Zn (30
> > electron), is this value difference can be used to make a guess about
> > different ions?
> > is there any way we can find the electron density value at different peaks?
> >
> > Thank you
> >
> > Veerendra
>
--
Ethan A Merritt
Biomolecular Structure Center, K-428 Health Sciences Bldg
University of Washington, Seattle 98195-7742
