Hi Francis, As you may have guessed - my question is stems from my recent acquisition of some native data for a protein that I have lots of SAXS data for.
I suspect that more conventional MR is unlikely to work in this case as I only have a half-decent phasing model for ~30% of the protein (2 copies in the ASU, so 2x15%). I figured that seeing as I had all this SAXS data (and I have many datasets collected at multiple synchrotrons that all give very consistent results), I might as well have a pop at phasing with it. I have an Fsearch run running at the moment using Flms generated from the Crysol program (ATSAS package) - no output as yet - does this program only output results to the log file at the end of the run? I have about 6 weeks until my next available synchrotron time, where derivatives will be screened, better resolution native data will hopefully be obtained, etc. In the meantime... Cheers, Dave ============================ David C. Briggs PhD Father, Structural Biologist and Sceptic ============================ University of Manchester E-mail: david.c.bri...@manchester.ac.uk ============================ Webs : http://flavors.me/xtaldave Twitter: @xtaldave Skype: DocDCB ============================ On 12 March 2012 22:09, Francis E Reyes <francis.re...@colorado.edu> wrote: > Hi David > > I'm the original poster you mention in your email, and I'm sad to report I > never really got anywhere with the initial inquiry outside of James Holton's > original response. > > The good news is that I was able to solve the structure I mentioned at 4A. > (albeit through other means). > > > From my own literature research I can vaguely remember that bridging the > SAXS resolution to the X-ray resolution required measuring some really low > angle reflections in the x-ray data (100-20A). And of course it's the phase > extension piece that James refers to. (20A to 4A is a hell of a jump). > However, even John Tainer has suggested that SAXS envelopes can be used to > locate heavy atoms in isomorphous or anomalous difference data, though this > has yet to be shown in practice. Depending on the heavy atom this can > certainly help with the phase extension. > > > Was your question academic, or are you, like I was, stuck in low resolution > land with no phases? (I can certainly assist with the latter). > > > F > > > > > > > On Mar 12, 2012, at 2:10 PM, David Briggs wrote: > >> Hi CCP4bb, >> >> I would like to ask about "envelope phasing" - specifically with SAXS data. >> >> There are papers (1) and tutorials (2) describing how this might be >> done, but I have also found comments on the ccp4bb, such as this one >> (http://www.proteincrystallography.org/ccp4bb/message11690.html) which >> are somewhat less optimistic. >> >> I get the impression from my reading around that SAXS envelope phasing >> is somewhat difficult to do unless you have some NCS you can use to >> help the phase extension process. Does anybody have any >> opinions/evidence/examples/anecdotes/tips about how SAXS envelope >> phasing can be done successfully? >> >> Cheers, >> >> Dave >> >> (1) - eg - http://scripts.iucr.org/cgi-bin/paper?dz5081 >> (2) - eg - >> http://www.phaser.cimr.cam.ac.uk/index.php/Using_Electron_Density_as_a_Model >> >> ============================ >> David C. Briggs PhD >> Father, Structural Biologist and Sceptic >> ============================ >> University of Manchester E-mail: >> david.c.bri...@manchester.ac.uk >> ============================ >> Webs : http://flavors.me/xtaldave >> Twitter: @xtaldave >> Skype: DocDCB >> ============================ > > > > --------------------------------------------- > Francis E. Reyes M.Sc. > 215 UCB > University of Colorado at Boulder > > > > >
