Hello,
I had recently collected and solved the phases for a protein molecule using
CCP4 and the ShelXCDE SAD method in it. What I was wondering was that the
peaks for the three SE incorporated methionines are there as expected, but
there is one peak scored roughly as the second largest where
Unexpected peaks in a S-SAD experiment sometimes turn out to be chloride,
sulfate or a metal ion. I would suggest that you run shelxd with and
without the disulfide option (or with different numbers of disulfides)
to see which is best, and also run SHELXE with the -b flag set. This will
There is ALWAYS anomalous scattering. You do not have be at the
absorption edge to get it. The question is just whether your experiment
is good enough to detect it.
So your question of overlapping always has the answer Yes, but I would
remove the words absorption edge from your question.
On Thursday 25 September 2008 08:45:10 Michael Jackson wrote:
This data was collected at 0.97960 Angstroms which is close to the peak
Xray absorption edge for Se but does anyone know if a disulfide has any
absorption edge overlapping here?
Your case might be different, but it could also be a true Se signal from
Se-Cys incorporated into your protein during Se-Met expression. Depending
on the protocol you used, Se may get incorporated into Cys, especially if
only source of sulfur is Se-Met. We have seen such signals from Cys-
