in our structural genomics project ( http://s2f.umbi.umd.edu/
) we try to have at least
one Se per 60 to 80 aa. Don't count on the N-terminal Met, it is (if
present) often disorderd.
There are some rare cases were more than 100 aa were phased with one
Se-site.
It is however possible, that other Met-site chains are disorderd as
well.
I had one case were nearly half of my Se were disorderd.
Also importend is Your crystall quality. If You have small B You may
need less Met.
The beam line is of also very importend, take a fluorescence scan and
(it is prob. not
in Your hands, but.. ) the wavelength has to be stable.
We have good experience with engineering additionally Met into proteins.
Leu and Phe are good candidates.
Good luck
(:hristopher
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*** CCP4 home page http://www.ccp4.ac.uk ***Hi all,
just a general question about Se-MAD phasing: how many Met are nescessary compared to the number of aar for a Se-Met-MAD phasing??
Tanja
Thanks in advance,
-- Dr. Christopher Lehmann Center for Advanced fon: ++(301)-738-6126 Research in Biotechnology fax: ++(301)-738-6255 9600 Gudelsky Drive e-mail: lehmann@umbi.umd.edu Rockville, MD 20850, USA web: http://www.geocities.com/dr_christopher_lehmann/