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Hi Peter,
You could:
1) Ttry numerous different cryoprotectants.
2) Try variations of the DNA length and overhangs. You might then
get improved crystals in same space group or get a different space group
which may allow you to get away with less than 90 degrees of data
collection (presumably, you are not able to do that now?)
3) If the streakiness is not too bad, you could try increasing the
sample-detector distance to be able to resolve part of the streaky spots
and integrate them or try mounting the crystal in different
orientations to see if that will improve anything
4) try annealing the crystal after it has been mounted. Block the
cryostream for ~10 seconds and then allow it to freeze back
5) try soaking the crystals in some heavy atom solutions at
different concentrations. Sometimes, heavy atoms have been seen to
improve lattice packing resulting in improved diffraction quality
6) If the protein crystallizes by itself without DNA, you could try
crystallizing the protein alone and then soaking it in DNA prior to data
collection and hope it binds
7) Are you now doing a one step cryosoak prior to freezing? If so,
you could try a multi-step soak, increasing the cryoprotectant conc.
slowly by serial soaking up to the final desired conc. before mounting.
8) If you are collecting at a synchrotron source, you could try
different exposure times. You might be able to reduce radiation damage
and get better diffraction.
9) If your current crystals are from hanging drops, you could try
sitting drops, or vice versa.
10) "Very good" data sets are often not necessary to solve
structures, depending on the case (MR, SAD, MIR, etc.) since so many
things like resolution, heavy atom signal, etc. are also involved
Hope some of this helps.
-Debanu.
--
Debanu Das,
University of California,
Berkeley.
W.M. B. wrote:
Hi there:
I am crystallizing a protein-dna complex. The diffraction from one
direction is very good. when the crystal turns 90 degree, it has
streaking diffraction. I can't get a very good dataset in order to
solve the structure.
The crystal is good-looking like the cubic ice. I'm tring to
crystalize the complex from different conditions. Is there any other
way to improve the diffraction? Any suggestion would be greatly
appreciated.
Peter
