Role of a Cysteine Synthase in Staphylococcus aureus

Abstract

The gram-positive human pathogen Staphylococcus aureus is often isolated with media containing potassium tellurite, to which it has a higher level of resistance than Escherichia coli. The S. aureus cysM gene was isolated in a screen for genes that would increase the level of tellurite resistance of E. coli DH5␣. The protein encoded by S. aureus cysM is sequentially and functionally homologous to the O-acetylserine (thiol)-lyase B family of cysteine synthase proteins. An S. aureus cysM knockout mutant grows poorly in cysteine-limiting conditions, and analysis of the thiol content in cell extracts showed that the cysM mutant produced significantly less cysteine than wild-type S. aureus SH1000. S. aureus SH1000 cannot use sulfate, sulfite, or sulfonates as the source of sulfur in cysteine biosynthesis, which is explained by the absence of genes required for the uptake and reduction of these compounds in the S. aureus genome. S. aureus SH1000, however, can utilize thiosulfate, sulfide, or glutathione as the sole source of sulfur. Mutation of cysM caused increased sensitivity of S. aureus to tellurite, hydrogen peroxide, acid, and diamide and also significantly reduced the ability of S. aureus to recover from starvation in amino acid-or phosphate-limiting conditions, indicating a role for cysteine in the S. aureus stress response and survival mechanisms.

Control of Copper Resistance and Inorganic Sulfur Metabolism by Paralogous Regulators in Staphylococcus aureus

“…We establish here that S. aureus strain Newman is able to grow on thiosulfate as the sole sulfur source (36). Thiosulfate is a major excreted sulfur-containing compound in humans, and is thought to be generated by the oxidation of bacterially derived H 2 S by an essential mitochondrial sulfur dioxygenase in mucosal cells to protect against sulfide toxicity (30).…”

“…Sulfite and alkylsulfonates, e.g. taurine, are likewise not assimilated and sulfite cannot be metabolized (35,36). Organic sulfur sources, including glutathione and homocysteine, are preferred sources of cysteine, but both must be acquired by S. aureus from the host.…”

“…The Cu(I) binding affinity (K Cu ) was further quantified using an anaerobic bathocuprione disulfonate competition assay with log K Cu determined to be 18.1 Ϯ 0.5 (supplemental Table S1). Substitution of Cys 41 or His 66 (equivalent to essential residues Cys 36 and His 61 in Mtb CsoR) (13) with alanine results in a significant decrease in K Cu , with log K Cu of 14.5 Ϯ 0.1 and 15.3 Ϯ 0.1 for C41A and H66A CsoRs, respectively (supplemental Table S1). …”

“…All CsoR family proteins lack a known canonical DNA binding domain and are projected to adopt the flat disc-shaped dimer of dimers homotetrameric structure characteristic of Cu(I)-sensing CsoRs, with individual dimers consisting of an antiparallel four-helix bundle flanked by a C-terminal ␣3 helix (13,14). Two cysteine residues on opposite subunits within a dimer make coordination bonds to the Cu(I) ion, with the third ligand a His from the ␣2 helix (Cys 36 Ј, His 61 , Cys 65 ), thus completing a trigonal S 2 N coordination complex (13). Additionally, two conserved second coordination shell residues, Tyr 35 Ј and Glu 81 , play critical roles in driving allosteric negative regulation of DNA binding by Cu(I) within the tetramer (15,16).…”

Staphylococcus aureus CymR Is a New Thiol-based Oxidation-sensing Regulator of Stress Resistance and Oxidative Response

“…Perhaps not surprisingly, deletion of cymR makes S. aureus more sensitive to hydrogen peroxide, tellurite, and other stresses (20), which can be attributed to its function as a regulator of ROS detoxification genes such as ahpFC, as well as cysteine biosynthesis genes such as cysM and mccAB. In S. aureus, cysteine is considered to be one of the major components of the cellular reducing buffer because of the absence of GSH biosynthesis (21)(22)(23). Despite past studies of CymR, the exact sensing and regulatory mechanism of this master regulator have yet to be elucidated.…”