Thank you so much

From: Eleanor Dodson <eleanor.dod...@york.ac.uk>
Date: Monday, May 6, 2024 at 3:30 PM
To: Liliana Margent <lmarg...@gradcenter.cuny.edu>
Cc: CCP4BB@jiscmail.ac.uk <CCP4BB@jiscmail.ac.uk>
Subject: [EXTERNAL]Re: [ccp4bb] Modeling Disulfide Bond Occupancies
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Well - I turn off occupancy refinement once there is a sort of consensus..
Disulphides often break after long exposures and you see the positive and 
negative blobs clearly. I must admit I usually just set 0.5 as occ , fix the 
surviving disulphide link and let the B values suggest a better ratio than 
o.5:0.5..
Eleanor

On Mon, 6 May 2024 at 20:20, Liliana Margent 
<lmarg...@gradcenter.cuny.edu<mailto:lmarg...@gradcenter.cuny.edu>> wrote:
Greetings everyone,

I'm currently in the process of modeling a disulfide bond in two structures. 
However, when I attempt to model single occupancy for the cysteines involved in 
the bond, negative density blobs emerge within the disulfide bond. This 
suggests the possibility of alternate conformations for the cysteines.

Yet, when I endeavor to model alternate conformations for both cysteines, their 
occupancies do not align despite running refinement with a bond parameter file 
that specifies the link. To illustrate, I initiate the refinement with 
occupancies for Cys472 as A0.75/B0.25 and for C384 as A0.75/B0.25, but 
post-refinement, the output occupancies appear as Cys472 A0.84/B0.16 and for 
C384 A0.97/B0.03. Where A confs participate in the s-s bond.

Has anyone else encountered this issue before, or does anyone have suggestions 
on how to refine these cysteines to achieve coherent occupancies?

Thank you for any insights you can provide.

Best,
Liliana

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