Re: [ccp4bb] bigger size - > better diffraction?

- Protein crystallography

Main steps:

- Protein purification
- Crystallisation

Special:

- Programs for crystallography
- X-ray detectors

Basic tutorials:

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   - Amino Acids

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Detwinning
From: "Sundaramoorthy, Munirathinam" m {- dot -} sundaramoorthy {- at -} VANDERBILT {- dot -} EDU
Date: 2007-04-04

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Subject: Re: bigger size - > better diffraction?
From: Shane Atwell satwell {- at -} SGXPHARMA {- dot -} COM
Date: 2007-04-04

Subject: Re: bigger size - > better diffraction?
From: artem {- at -} XTALS {- dot -} ORG artem {- at -} XTALS {- dot -} ORG
Date: 2007-04-04

Hello Jenny,

0.2 Rmerge may be an indication of incorrectly assigned SG or perhaps a
misindexing by one, etc. Check what happens if you reprocess in P4.

For a 10kDa protein, your unit cell is kind of large - depending of course
on the symmetry, the higher obviusly the better. I would bet that you have
pretty high solvent content - nothing scientific about this prediction,
merely personal experience with several small proteins that crystallized
in high-symmetry SG and had >80% solvent.

What you may want to do is to very carefully study your cryo. When we were
working on a structure of FliS-FliC
complex(http://www.xtals.org/pdfs/FliC_FliS.pdf), the only way to freeze
the crystals correctly was to increase the concentration of sulfate ion in
the cryoprotectant. It later turned out that we had a sulfate ion bridging
a symmetry threefold, and in low sulfate the ion would leave, resultuing
in disorder in the crystals.

Ultimately, if you've already tried all the 'standard' tricks, such as
additives, glycerol/eg in the condition, replacing NaCl with an exotic
salt such as KCl, CsCl, RbCl, and so forth - perhaps you may want to
consider adjusting the surface of the protein. I would be glad to help you
with that.

Artem

CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Detwinning
From: "Sundaramoorthy, Munirathinam" m {- dot -} sundaramoorthy {- at -} VANDERBILT {- dot -} EDU
Date: 2007-04-04

Next message:
Subject: Re: bigger size - > better diffraction?
From: Shane Atwell satwell {- at -} SGXPHARMA {- dot -} COM
Date: 2007-04-04