OK, here's a concrete case:
A 150kDa protein complex, the plate-like crystals can be produced in
sufficient number; Se-Met derivatives available, total number of Met
around 20, subunits could be marked and combined individually.
Diffraction is highly anisotropic, in certain directions up to
3.8A,while in others only 5A. Similarly, the spot quality is very
dependent on orientation.
Space group I222, a=75 b=150 c=250. Datsets scale well with 3-4% Rsym
up to 12 A resolution. At 4.5A Rsym rises above 50% (I/sigma is still
at 2.0). The 'sweet' slices of the dataset scale significantly better,
but give only 70% (non-anomalous) completness. We hope to improve
datasets slightly by orienting the crystals.
65% of the structure would be available as coordinate building blocks
from the PDB, however, MR with these components so far did not yield a
clear solution.
Any suggestions or experiences with similar cases are welcome.
Cheers,
Clemens
Zitat von Clemens Vonrhein <vonrh...@globalphasing.com>:
[Show Quoted Text - 64 lines][Zitattext verstecken]
Hi Clemens,
maybe re-phrasing your question:
What would be the best technique/strategy to phase crystals that
[ ] diffract to maximal ___ A
[ ] typical diffraction to __ A
[ ] are radiation sensitive
[ ] easily reproducable
[ ] large crystals (up to ___ um)
[ ] long needles
[ ] thin plates
[ ] have ___ mol/asu
[ ] spacegroup ___
[ ] nice diffraction pattern
[ ] poor diffraction pattern (reason: ___)
[ ] anisotropic diffraction (resolution in poorest direction: ___ A)
[ ] cell dimensions of roughly ___ ___ ___ ___ ___ ___
[ ] purified from native source
[ ] expressed in expression system ___
[ ] anything else: _______
Tick the appropriate boxes and fill out the blanks as much as possible
- that should give more important and necessary information. There are
consequences to consider for all of those points that would then give
some rough guidelines for your particular project/problem.
Maybe CCP4 should have an online form to describe a particular
crystallographic problem?
Cheers
Clemens
On Thu, May 14, 2009 at 09:35:28AM +0200, Clemens Grimm wrote:
Dear all,
after the SeMet phasing discussion, what would be -in general- the best
technique to phase low resolution data (<=4A) of large complexes (>=150
kDA) - in terms of
- derivatization compounds (is there something like the 'golden five' HA
compounds for these cases),
- data collection techniques and
- phasing methods?
Clemens
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