CysK2 from Mycobacterium tuberculosis Is an O-Phospho-L-Serine-Dependent S-Sulfocysteine Synthase
2014 (English)In: Journal of Bacteriology, ISSN 0021-9193, E-ISSN 1098-5530, Vol. 196, no 19, 3410-3420 p.Article in journal (Refereed) Published
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 k(max)/K-s = (3.97 x 10(3)) +/- 619 M-1 s(-1), which compares well to the OPS-specific mycobacterial cysteine synthase CysM with a k(max)/K-s of (1.34 x 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 k(cat)/K-m 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.
Place, publisher, year, edition, pages
2014. Vol. 196, no 19, 3410-3420 p.
Acetylserine Sulfhydrylase, Cysteine Synthase, Salmonella-Typhimurium, Gene-Expression, Mechanism, Biosynthesis, Mycothiol, Enzyme, Identification, Intermediate
IdentifiersURN: urn:nbn:se:kth:diva-152554DOI: 10.1128/JB.01851-14ISI: 000341237500006ScopusID: 2-s2.0-84907016411OAI: oai:DiVA.org:kth-152554DiVA: diva2:750677
QC 201409292014-09-292014-09-292014-09-29Bibliographically approved