Zn and Se have similar f' and f''. Why Zn seems have much better phasing powder in practice? Is it just because Zn always binds tightly on protein but Se might have higher b-factor?
Guangyu On 5/14/09 2:31 PM, "Pete Meyer" <pame...@mcw.edu> wrote: > 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 <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 >> >> -- >> >> *************************************************************** >> * Clemens Vonrhein, Ph.D. vonrhein AT GlobalPhasing DOT com >> * >> * Global Phasing Ltd. >> * Sheraton House, Castle Park >> * Cambridge CB3 0AX, UK >> *-------------------------------------------------------------- >> * BUSTER Development Group (http://www.globalphasing.com) >> ***************************************************************
