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Re: [ccp4bb]: Q: disulphide reduction in protein structures



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Hi Wai,

Did you measure the distance between the sulphurs. It should be ~2.05
Angstrom for a disulphide bond and more than 3 Angstrom for a nonbonded
contact. If it truly is reduced, look at the CB-SG-SG-CB torsion angle,
this likes to be naer +/- 90 degrees. If disulphide bond formation would
have to indroduce large distortions, then that may stabilize a reduced
state. Are both cysteines conserved among related sequences, do they
sometimes have only one cysteine or do they always have either two or
none? The first and last cases would suggest a special interaction,
whereas the middle one suggests that the cysteine is "just a hydrophobic
burried residue". No guarantees either way though.

Bart

On Thu, 17 Feb 2000, Yu Wai Chen wrote:

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> ***    CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html    ***
> 
> Dear all,
> 
> Sorry this is not a CCP4 question.
> 
> Can buried (i.e. small or no solvent accessible surface area) disulphide
> bonds be reduced to cysteines in general?  I have a structure in which 2
> cysteines are in the right position to form a S-S bond but the electron
> density shows otherwise.  My protein was purified in reducing
> conditions.  However, from other evidences (structure homology), these
> should form S-S.  Does anyone know of any published structure that can
> shed light on my puzzle?  Thanks a lot.
> 
> Wai
> -- 
> ===================================================================
> Yu Wai CHEN, Ph.D. ..................   email:ywc@mrc-lmb.cam.ac.uk
>  Centre for Protein Engineering,             tel:+44-(0)1223-402148
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