I agree. Searching with a larger unit is likely to be successful if you
have a good idea of the structure of that larger unit. We had an example
of a low homology (29% identity) MR situation with 8 subunits per ASU
with twinned data. Not solvable with monomers. Solvable with a dimer
search model, then feeding that solution to Parrot and Buccaneer for
density modification and automated chain-building using 8-fold NCS.
Buccaneer built about 95%+ of the structure correctly.
Cheers,
_______________________________________
Roger S. Rowlett
Gordon & Dorothy Kline Professor
Department of Chemistry
Colgate University
13 Oak Drive
Hamilton, NY 13346
tel: (315)-228-7245
ofc: (315)-228-7395
fax: (315)-228-7935
email: [email protected]
On 1/20/2014 8:41 AM, David Schuller wrote:
Is the monomer the biggest unit you have to search with? If there is a
dimer, tetramer, etc. that is conserved, you could try searching with
that.
On 01/19/14 14:30, Chris Fage wrote:
Thank you all for your responses. I already have a few ideas about
how to approach the problem.
One of my concerns with so monomers per asymmetric unit at lower
resolution was the failure of MR software. Neither PHENIX nor Phaser
MR have made progress. I am fairly new to anomalous methods, having
solved only two structures by SeMet-based SAD. I've certainly picked
up on a number of tricks from the recent messages on heavy atoms, but
I thought my case might be a little unusual. I am confident the space
group is P1, as it was the only viable option when I indexed four
clean albeit low-res datasets.
The monomers are ~38 kDa, and the crystals diffracted to 3.4-3.0 at a
synchrotron.
The conditions for both native and SeMet crystals are:
8-12% PEG 2000 MME, 0.2 M ammonium sulfate, 0.1 M sodium acetate pH 5.5.
Macromolecular seeding of native crystals into SeMet drops yields the
needle-like crystals.
Any further input is greatly appreciated!
Regards,
Chris
On Sat, Jan 18, 2014 at 11:14 AM, Chris Fage <[email protected]
<mailto:[email protected]>> wrote:
Hello Everyone,
I am currently trying to phase a structure with an asymmetric
unit predicted to contain 20-24 monomers (space group P1). The
native crystals, while beautiful in appearance (see attached),
only diffract to ~3.4-3.0 angstroms at best, and SeMet-derived
crystals grow with poor morphology (small needles). Also, based a
fluorescence scan, I know that mercury does not bind appreciably.
Other than screening for a new space group, what options might I
have for phasing this many monomers at lower resolution? Is there
any real chance of solving the structure in this space group?
Thank you in advance for any suggestions!
Regards,
Chris
--
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All Things Serve the Beam
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David J. Schuller
modern man in a post-modern world
MacCHESS, Cornell University
[email protected]
