Narayanan Ramasubbu wrote:
> Dear all:
> I am noticing that in some of my structures, at 1.5 A resolution, 1)
> there is some negative density around the C of the carboxyl groups.
> 2) I also notice the negative density around S in a disulfide region. It
> is as though the disulfide is broken.
>
> Could some body enlighten me on this feature?
>
Synchrotron radiation can cause free radical mediated damage to
proteins. The most frequently observed consequences are decarboxlation
of Asp and Glu, and the breakage of disulfide bonds. See, for example,
Wiek et al. (2000) PNAS 97, 623-628, and Leiros et al. (2001) Acta
Cryst. D 57, 488-497.
Cheers,
--
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