We recently solved a multi-SeMet data set with nasty
pseudotranslational symmetry by telling lies to the software:
"we" (meaning my long-suffering student) indexed it in the
smaller unit cell by picking only the dark spots, found the Se
atoms in that cell, then reconstructed the larger cell
according to the native patterson peak. Even though it
initially forced 3 copies to be mathematically identical when
they really aren't quite (thus giving rise to the weak spots
and larger unit cell), it worked splendidly when nothing else did.
Phoebe
---- Original message ----
>Date: Fri, 5 Mar 2010 18:52:32 -0500
>From: Dhirendra K Simanshu <[log in to unmask]>
>Subject: [ccp4bb] Need help for phasing using Tantalum
bromide cluster
>To: [log in to unmask]
>
> Dear all,
> I am trying to phase 172 aa protein using tantalum
> bromide (Ta6Br12) cluster. Data belongs to space
> group C2221 with 4 molecules (2 dimers) in the
> asymmetric unit. Phenix.xtriage indicates presence
> of pseudo-translation (peak height= 39). I have
> collected data at Ta peak (1.2550 A) to a resolution
> of 2.9A, Ta inflection (1.2553 A) at 2.8 A using
> one crystal. I also collected one high energy remote
> (1.059 A) data at 2.6 A using another soaked
> crystal. All three datasets shows presence of very
> good anomalous signal till the highest resolution
> shell.
> Soaking with Tantalum bromide has changed the unit
> cell axes "a" and "b" by 4-5 A so it is no longer
> isomorphous with the native data (2.7 A). But since
> anomalous signal is very high in all these Ta soaked
> datasets, I have been trying to find a solution
> using SAD/MAD but without any success. Processing
> data in lower symmetry P21 and C2 also doesn't help.
> Another noticeable thing is..... "scalepack2mtz"
> fails when I try to run to convert my sca file into
> mtz (using CTRUNCATE option ON) with error saying
> "Anisotropic correction failed - negative eigen
> value".
> Since finding a solution has not been possible for
> reasons unclear to me. I guess I am having problem
> because of presence of pseudo-translational symmetry
> in my crystal. I would be grateful for any helpful
> advice or suggestions in this regard.
> Thanks in advance!
> Regards
> Dhirendra
Phoebe A. Rice
Assoc. Prof., Dept. of Biochemistry & Molecular Biology
The University of Chicago
phone 773 834 1723
http://bmb.bsd.uchicago.edu/Faculty_and_Research/01_Faculty/01_Faculty_Alphabetically.php?faculty_id=123
RNA is really nifty
DNA is over fifty
We have put them
both in one book
Please do take a
really good look
http://www.rsc.org/shop/books/2008/9780854042722.asp
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