On 04/30/12 11:41, Ke, Jiyuan wrote:
Dear All,
I have a question regarding solving a crystal structure by molecular
replacement. It is a single protein with a molecular weight of 25.5
kDa. The cell dimension is rather big from the diffraction data ( 90.9
Å, 143.9 Å, 216.3Å, 90°, 90°, 90°). The possible space group is
P212121. With such a big unit cell, we predicted that there are 8-10
molecules per asymmetric unit. We have a decent model with sequence
similarity of 49%. I tried several times with Phaser search with the
current model and had difficulty to find any clear solution. Has
anyone seen such cases and any suggestions to solve the structure? Thanks!
I solved 8 copies with 32% identity to the search model (1ZL9). I used
BEAST for the MR, in the days before Phaser.
You say you have a single protein, which I interpret to mean that the
active unit is a monomer. Bummer, searching with a multimer would
certainly simplify things.
See that your search model is compact. Is the search model a single
domain? Does the sequence similarity extend throughout the entire thing?
Are there loops which should be clipped?
With such a large number of monomers, translation-only NCS seems likely,
so be on the lookout for that.
--
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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]
