Hello everyone,
We are working on a protein in which a long loop is held in place by a
disulphide bond. All the biochemistry and biophysics of this protein
indicates that the disulphide bond should be intact, but we only see
one end of it in the crystal structure. The protein has not been
exposed to any reductants. The data were collected at a medium
intensity synchrotron source (MAX-lab in Lund) and the total dose
should thus not have been extremely high. We have even looked at maps
calculated from the first half of the dataset (45 minutes exposure vs.
90) and there is no difference. We have tried to react the free
cysteine with 1mM MeHgCl2 and 10mM iodacetamide, to no avail. Thus we
really think the disulphide is intact even in the crystal.
Has anyone seen a similar case, where all evidence pointed to an
intact disulphide but it was not visible in the density?
Thanks
Derek
__________________________________________________________________
Derek Logan tel: +46 46 222 1443
Associate Professor fax: +46 46 222 4692
Molecular Biophysics mob: +46 76 8585 707
Centre for Molecular Protein Science
Lund University, Box 124, 221 00 Lund, Sweden
