|
type |
Journal Article |
authors |
O'Leary SE, Jurgenson CT, Begley TP, Ealick SE.
|
title |
O-phospho-L-serine and the thiocarboxylated sulfur carrier protein CysO-COSH are substrates for CysM, a cysteine synthase from Mycobacterium tuberculosis. |
journal |
Biochemistry |
Activity |
2.5.1.113 |
Family |
2.5.1.113 |
sel |
selected |
ui |
18842002 |
year |
(2008) |
volume |
47 |
number |
44 |
pages |
11606-15 |
| |
keywords |
doi: 10.1021/bi8013664 |
abstract |
The kinetic pathway of CysM, a cysteine synthase from Mycobacterium tuberculosis, was studied by transient-state kinetic techniques. The expression of which is upregulated under conditions of oxidative stress. This enzyme exhibits extensive homology with the B-isozymes of the well-studied O-acetylserine sulfhydrylase family and employs a similar chemical mechanism involving a stable alpha-aminoacrylate intermediate. However, we show that specificity of CysM for its amino acid substrate is more than 500-fold greater for O-phospho-L-serine than for O-acetyl-L-serine, suggesting that O-phospho-L-serine is the likely substrate in vivo. We also investigated the kinetics of the carbon-sulfur bond-forming reaction between the CysM-bound alpha-aminoacrylate intermediate and the thiocarboxylated sulfur carrier protein, CysO-COSH. The specificity of CysM for this physiological sulfide equivalent is more than 3 orders of magnitude greater than that for bisulfide. Moreover, the kinetics of this latter reaction are limited by association of the proteins, while the reaction with bisulfide is consistent with a rapid equilibrium binding model. We interpret this finding to suggest that the CysM active site with the bound aminoacrylate intermediate is protected from solvent and that binding of CysO-COSH produces a conformational change allowing rapid sulfur transfer. This study represents the first detailed kinetic characterization of sulfide transfer from a sulfide carrier protein. |
last changed |
2016/10/04 16:09 |
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