RE: [ccp4bb]: Disulfide bridge

["Hurley, Thomas D." <thurley@iupui.edu>]

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Darrell,

What is the peak height for that "extra density" and what is the distance between the unconstrained sulfur atoms in the cysteines?  It is certainly possible that it is a metal ion.  Any other possible metal coordination side chains - His, Asp, Glu - in the vicinity of this "disulfide"?  Another possibility is that the disulfide is partially reduced in your structure (or partially oxidized pair of Cysteines, depending on you redox point of view) and that the density simply represents the average of two distinct species, are there difference peaks near the C-beta atoms indicative of different positions for this atom as well - eg. discrete disorder?

Tom Hurley

-----Original Message-----
From: deh22@cornell.edu [mailto:deh22@cornell.edu]
Sent: Wednesday, September 11, 2002 10:09 AM
To: ccp4bb@dl.ac.uk; o-info@origo.imsb.au.dk
Subject: [ccp4bb]: Disulfide bridge


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Dear all,

Has anyone ever seen a disulfide bridge that looks something like this:

Cys-S-?-S-Cys

If I force the disulfide bridge, the geometry does not fit the density
at all.  If I let the sulfurs fit into the density correctly, the
geometry does not work for a disulfide, although there is very clear
density between the sulfurs.

Any suggestions?

Thanks,
Darrell Hurt