[ccp4bb] histidine modification

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

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From: Donnie Berkholz dberkholz {- at -} GENTOO {- dot -} ORG
Date: 2008-07-10

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Subject: Re: histidine modification
From: artem {- at -} XTALS {- dot -} ORG artem {- at -} XTALS {- dot -} ORG
Date: 2008-07-11

Subject: histidine modification
From: alexander {- dot -} singer {- at -} UTORONTO {- dot -} CA alexander {- dot -} singer {- at -} UTORONTO {- dot -} CA
Date: 2008-07-11

Hi -- I am close to finishing up a protein structure of an aldo-keto
reductase but for a modification of a histidine residue shown here
(one in each molecule of the AU). Note the following electron density
in which this residue in both molecules of the AU was mutated to an
Ala, Refmac'd for 5 cycles and then 2fofc and fofc maps are shown.
Resolution goes to 1.6 A, and the Rwork/Rfree is 16/18.9%. However
this modification flumoxes me and I was hoping someone (someone!!) has
seen something like this before. This crystal was shot at LS-CAT but
I see something similar with a slightly lower resolution crystal I
shot on our homesourse Raxis4. Crystallization conditions are 0.2M Ca
Acetate, 9% PEG 8K,0.1M Na Cacodylate pH6.5, Cryo- 25%Et.Glycol.
Other people have suggested this may be a modification of the
cacodylate, however the cacodylate modifications I've seen in the
lit/pdb seem to refer to modifs of cysteine in which the arsenic
contains two oxygens attached to the arsenic atom which is in turn
bound to the cysteine sulfur. However in this case, there we seem to
have at least 4 atoms shown coming off the Nepsilon of the his residue.

Thank you for your time.

Alex Singer

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

Next message:
Subject: Re: histidine modification
From: artem {- at -} XTALS {- dot -} ORG artem {- at -} XTALS {- dot -} ORG
Date: 2008-07-11