|
type |
Journal Article |
authors |
Steiner EM, Böth D, Lössl P, Vilaplana F, Schnell R, Schneider G. |
title |
CysK2 from Mycobacterium tuberculosis is an O-phospho-L-serine-dependent S-sulfocysteine synthase. |
journal |
J Bacteriol |
Activity |
2.8.5.1 |
Family |
2.8.5.1 |
PLP Fold Type |
2 |
sel |
selected |
ui |
25022854 |
year |
(2014) |
volume |
196 |
number |
19 |
pages |
3410-20 |
| |
abstract |
Mycobacterium tuberculosis is dependent on cysteine biosynthesis, and reduced sulfur compounds such as mycothiol synthesized from cysteine serve in first-line defense mechanisms against oxidative stress imposed by macrophages. Two biosynthetic routes to l-cysteine, each with its own specific cysteine synthase (CysK1 and CysM), have been described in M. tuberculosis, but the function of a third putative sulfhydrylase in this pathogen, CysK2, has remained elusive. We present biochemical and biophysical evidence that CysK2 is an S-sulfocysteine synthase, utilizing O-phosphoserine (OPS) and thiosulfate as substrates. The enzyme uses a mechanism via a central aminoacrylate intermediate that is similar to that of other members of this pyridoxal phosphate-dependent enzyme family. The apparent second-order rate of the first half-reaction with OPS was determined as kmax/Ks = (3.97 × 10(3)) ± 619 M(-1) s(-1), which compares well to the OPS-specific mycobacterial cysteine synthase CysM with a kmax/Ks of (1.34 × 10(3)) ± 48.2. Notably, CysK2 does not utilize thiocarboxylated CysO as a sulfur donor but accepts thiosulfate and sulfide as donor substrates. The specificity constant kcat/Km for thiosulfate is 40-fold higher than for sulfide, suggesting an annotation as S-sulfocysteine synthase. Mycobacterial CysK2 thus provides a third metabolic route to cysteine, either directly using sulfide as donor or indirectly via S-sulfocysteine. Hypothetically, S-sulfocysteine could also act as a signaling molecule triggering additional responses in redox defense in the pathogen upon exposure to reactive oxygen species during dormancy. |
last changed |
2018/06/04 12:01 |
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