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Thioester bonds

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Dennison

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May 7, 1998, 3:00:00 AM5/7/98
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Does anyone know how thioester bonds would react to the conditions
typically used in reducing (Laemmli) SDS-PAGE? Is the pH per se high
enough to break them?
Any info and refs would be appreciated.
Cheers
Clive

Rob

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May 8, 1998, 3:00:00 AM5/8/98
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In article <3551AB...@unpsun1.cc.unp.ac.za>, Dennison
<denn...@unpsun1.cc.unp.ac.za> wrote:

Clive
Thioester bonds are broken in reducing SDS PAGE sample buffer. However,
omit the 2-ME and/or DTT from the sample buffer and they will survive SDS
PAGE. There are many references to this, in particular relating to
thiolesters between ubiquitin and active site cysteines in ubiquitin
pathway enzymes. Try: Chen & Pickart (1990) J. Biol. Chem. 265,
21835-21842.
Rob

Shaun D. Black

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May 8, 1998, 3:00:00 AM5/8/98
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Greetings All,

mb...@mbn1.biochem.nottingham.ac.uk (Rob) wrote:

I believe that you mean "disulfide", rather than "thioester". Cysteine
residues can be oxidized to go from the thiol/mercaptan form to make
disulfides (R-S-S-R'). The reverse reaction, reduction, can be
accomplished readily by addition of thiols such as beta-mercaptoethanol or
DTT, as you noted.

"Thioesters" are found in the linkage of Coenzyme A to carboxylic acids
(such as fatty acids), and in certain complement factors. But, as a whole
they are rather rare in biology. Chemically (R-S-(C=O)-R'), they are
extremely labile and can be hydrolyzed by water (i.e., 2-ME not even required).

In a related vein, "thioethers" are found commonly in the side chain of
the amino acid Methionine (Met, M). Chemically, it is R-S-CH3, essentially
the thio-analogue of an ether. This linkage is rather stable and easily
survives boiling in the presence of thiols.

I hope these clarifications are useful to you.

Best regards,

Shaun


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
= Shaun D. Black, PhD | Internet e-mail address: sh...@uthct.edu =
= Dept. of Biochemistry | University of Texas Health Center at Tyler =
= Tyler, TX 75710 | World Wide Web: http://psyche.uthct.edu =
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=


Kojo Mensa-Wilmot

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May 9, 1998, 3:00:00 AM5/9/98
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Clive,

Thioesterification of proteins is not extremely rare in biology, as
suggested by the last post. The literature is replete with examples of
esterification of cysteine residues on proteins with fatty acids.
Palmitoylation (G-alpha proteins some G protein coupled receptors are
examples) and some and S-myristoylation (of phospholipase C) come to mind.
The bonds are susceptible to reducing agents like DTT especially at high
temperatures. So be careful.

With best wishes, Kojo
-----------------------------------------------------
Kojo Mensa-Wilmot
Dept. Cell Biology
724 Biological Sciences
University of Georgia
Athens GA 30602

Tel: 706-542-3355
FAX: 706-542-4271

----------
In article <980508214...@athena.uthct.edu>, sh...@uthct.edu (Shaun D.

Shaun D. Black

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May 11, 1998, 3:00:00 AM5/11/98
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Dear All,


"Kojo Mensa-Wilmot" <mens...@cb.uga.edu> wrote...

>Thioesterification of proteins is not extremely rare in biology, as
>suggested by the last post. The literature is replete with examples of
>esterification of cysteine residues on proteins with fatty acids.
>Palmitoylation (G-alpha proteins some G protein coupled receptors are
>examples) and some and S-myristoylation (of phospholipase C) come to mind.
>The bonds are susceptible to reducing agents like DTT especially at high
>temperatures. So be careful.

It is true that there are lots of examples of thioesters (my previous post
was meant to be illustrative, not a review), compared to the number of
Cys residues in the thousands of known proteins, thioesterification is
still rather a rare occurrence, all things considered.

For those who might want to read more about post- and co-translational
modifications of proteins, there is a very well-written book that you
might want to consult:

"Co- and Post-translation Modifications of Proteins: Chemical Principles
and Biological Effects" (D.J. Graves, B.L. Martin, and J.H. Wang, Eds.)
Oxford Press (New York) 1994.

travissc...@gmail.com

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Nov 25, 2017, 9:10:59 PM11/25/17
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On Thursday, May 7, 1998 at 2:00:00 AM UTC-5, Dennison wrote:
> Does anyone know how thioester bonds would react to the conditions
> typically used in reducing (Laemmli) SDS-PAGE? Is the pH per se high
> enough to break them?
> Any info and refs would be appreciated.
> Cheers
> Clive

Thioesters are formed transiently during decarboxylase reactions. The Breslow reaction scheme for pyruvate decarboxylase is incorrect; this actually involves the ring‐opening of thiamine, exposing an internal thiol which attacks the carbonyl carbon or pyruvate.

The resulting two carbon unit is then shifted to another thiol, this time the lipoic acid prosthetic group. It is then transferred to coenzyme A — yet another thiol.

So the thiol could perhaps be seen by it's ability to form low‐energy carbon bonds, useful for shuttling acyl and acetyl groups during metabolism. As previously mentioned by Rob, vide infra, these thiol molecules would be more likely to release their substrates in reducing conditions — perhaps yet another way in which the cell controls its oxidation rate.

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