Dear Rhys,
You may consider Xenon derivative, which could be prepared simply pressurizing
the protein crystals in a xenon chamber. It does not require any modification
of mother liquor. It just needs cryo-protectant where crystals are stable for
at least one to two mins. Higher Pressure (20 to 40 bar) and 1-2 min incubation
time are normally sufficient for binding of Xenon to proteins.
Xenon binds to pre existing hydrophobic cavities of proteins by dispersion
force. Xenon derivatives are highly isomorphous to native crystals. So SIRAS
phasing could be efficient. However if you consider collecting data at longer
wavelengths you could get anomalous signal from sulphur too. Weaker SAD or
SIRAS phases from Xenon derivative could be used to bootstrap the Sulphur
phasing.
Similarly Kr pressurisation could be tried. MAD experiment can be performed at
any tunable beamline but the disadvantage with this derivative is, it desorps
quickly during cooling after pressurisation leaving out with lower than 50-60%
occupancy.
Success of the Xenon/Krypton derivatisation depends on size of the proteins and
how stable your
crystals are under cryo-protectant.
The bigger the protein, higher the chance of Xe/Kr binding.
best
Santosh
Santosh Panjikar, Ph.D.
Scientist
Australian Synchrotron
800 Blackburn Road
Clayton VIC 3168
Australia
Ph: +61-4-67770815 (mobile)
+61-3-85404276 (office)
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