You might find Structure 14, 973-982 Jun 2006 of interest.
Larger protein, Zn instead of Se (although only 8 sites), roughly
comparable to slightly lower resolution. This was mainly testing to
confirm that there was enough anomalous signal to phase off of, so the
model was essentially known; however 50% completeness was enough to
allow for site location by anomalous or dispersive difference fourier
(which one sticking point...even if the MR hits don't give a helpful
model phased map, they can still be good enough for site location).
Pete
Clemens Grimm wrote:
> 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 <[log in to unmask]>:
>
>
> [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
>
> --
>
> ***************************************************************
> * Clemens Vonrhein, Ph.D. vonrhein AT GlobalPhasing DOT com
> *
> * Global Phasing Ltd.
> * Sheraton House, Castle Park
> * Cambridge CB3 0AX, UK
> *--------------------------------------------------------------
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