Try MR with one copy in all space groups of PG 321/312 using Phaser. Going from
PG 3 to PG 32 should halve the number of copies per ASU. You may have to
re-process your data in the higher point group to do this.
Or you might actually have a tetartohedral twin, but just try with the
Hi Keller,
Thanks for the suggestions! I only have two copies in ASU at SG P32. Zanuda
also suggests P32 is the best SG.
On Thu, Apr 13, 2017 at 8:12 PM, Keller, Jacob
wrote:
> Yes, this was my case exactly—it looks like there are two pairs of coupled
> twin domains:
Yes, this was my case exactly—it looks like there are two pairs of coupled twin
domains: a,c and b,d. Assuming you have multiple copies of your model in the
same ASU, try doing MR in higher symmetry space groups of point group 312 or
321, like P3212 etc. There is this handy page with all the
Hi Keller,
I do not how to check twin fraction after Refmac (I guess it's somewhere in
log file). From the log file it seems I have four twin domain:
Twin operators with estimated twin fractions
Twin operator: H, K, L: Fraction = 0.275; Equivalent operators: K,
-H-K, L; -H-K, H,
What was the refined twin fraction after Refmac? It’s much more accurate than
initial tests. Also, how many twin domains do you have? If you have many, it
might be a higher space group but with less twinning. I recently had a case in
which apparent tetartohedral (four-domain) twinning in P32
Twin refinement cannot be compared directly to untwinned - the R factors
are between different parameters - without twinning it is assumed you have
an amplitude obtained more or less from sqrt(I But for a twinned data set
that I is actually [ I1 + twin_factor I2 ] so the amplitude is not really
Hi Alex,
You are not giving the number after refinement without the twin refinement.
Nevertheless, R-free drops like this are not unheard of. You should check your
Refmac log file, it would warn you of potential space group errors. Refmac will
also give you a refined estimate of the twin
Dear All,
I have a protein/dna complex crystal and data collected at 3A and another
set at 2.8A, space group P32. L test shows twinning (fraction around 0.11).
The structure solved by MR and model building of the complex finish (no
solvent built yet, I do not think it's good to build solvent in
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Dear CCP4bb,
We work on an enzyme that we crystallized with two substrates bound in
the active site (the reaction transform two substrates into two
products). We have also the structure with the two products. We are
able to see densities for the substrates when we collect data at
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How are the peaks coordinated? Regular coordination with 5 or more ligands has
ion written all over it. Different difference density peak heights can be
caused by differences in effective B-factor restraint weight but also by
differences in relative scattering factors of oxygen and whatever you
It would be useful to know what wavelengths you were talking about. Also, try
an anomalous difference Fourier map to see whether the atoms are weakly
anomalous.
From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Andrew
Marshall
Sent: Thursday, April 13, 2017 2:00 AM
To:
Partially occupied Cs+ comes to mind. At lower resolution the difference may be
more easily fudged away by the refinement lowering the B.
Mark J van RaaijCNB-CSICwwwuser.csic.es/~mjvanraaij
Original message From: Andrew Marshall
Date:
Hello all,
I have a 1.8A structure (Rfree/Rwork = 20.5/17.4) with 1420 water molecules
modelled. There are approximately a dozen waters, all well structured with
hydrogen bonds to protein atoms, with positive difference density (>4sigma,
sometimes >5) at their centre. The only ions present in my
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