- Characterization of serine acetyltransferase (CysE) from methicillin-resistant Staphylococcus aureus and inhibitory effect of two natural products on CysE
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Methicillin-resistant Staphylococcus aureus (MRSA) is a major hospital-acquired infective pathogen that has developed resistance to many antibiotics. It is imperious to develop novel anti-MRSA drugs to control the emergence of drug resistance. The biosynthesis of cysteine in bacteria is catalyzed by CysE and CysK. CysE was predicted to be important for bacterial viability, it could be a potential drug target. The serine acetyltransferase activity of CysE was detected and its catalytic properties were also determined. CysE homology model was built to investigate interaction sites between CysE and substrate L-Ser or inhibitors by molecular docking. Docking data showed that residues Asp94 and His95 were essential for serine acetyltransferase activity of CysE, which were confirmed by site-directed mutagenesis. Colorimetric assay was used to screen natural products and six compounds which inhibited CysE activity (IC50 ranging from 29.83 μM to 203.13 μM) were found. Inhibition types of two compounds 4 (11-oxo-ebracteolatanolide B) and 30 ((4R,4aR)-dihydroxy-3-hydroxymethyl-7,7,10a-trimethyl-2,4,4a,5,6,6a,7,8,9,10,10a,l0b-dodecahydrophenanthro[3,2-b]furan-2-one) on CysE were determined. Compounds 4 and 30 showed inhibitory effect on MRSA growth (MIC at 12.5 μg/ml and 25 μg/ml) and mature biofilm. The established colorimetric assay will facilitate further high-throughput screening of CysE inhibitors from different compound libraries. The compounds 4 and 30 may offer structural basis for developing new anti-MRSA drugs.
- Chen, Changming,Yan, Qiulong,Tao, Mengxing,Shi, Huaying,Han, Xiuyan,Jia, Liqiu,Huang, Yukun,Zhao, Lizhe,Wang, Chao,Ma, Xiaochi,Ma, Yufang
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p. 218 - 226
(2019/04/17)
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- Synthesis method of Na-9-fluorenylmethoxycarbonyl-O-acetyl-L-serine
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The invention relates to a synthesis method of Na-9-fluorenylmethoxycarbonyl-O-acetyl-L-serine, mainly aiming at solving the technical problems that in the existing synthesis method, the aftertreatment operation is more troublesome since perchloric acid is taken as a catalyst, excessive acetyl chloride is used, and potential safety hazard is caused when ethyl ether is used for crystallizing. The method comprises the following steps: (1) dissolving solid L-serine into an acetic acid solution, dropwise adding liquid acetyl chloride, and stirring for carrying out reaction; adding the reaction liquid into a petroleum ether solution, separating out an intermediate O-acetyl-L-serine, filtering and drying; (2) dissolving the intermediate into a sodium carbonate solution, dropwise adding a 9-fluorene methyl-N-succinimido-carbonate solution dissolved in ethyl acetate, removing the excessive 9-fluorene methyl-N-succinimido-carbonate in a layering way, acidifying the water phase by using hydrochloric acid, then extracting by using an extracting agent-ethyl acetate, washing the obtained oil phase with water, removing the hydrochloric acid, and concentrating the oil phase for removing the extracting agent-ethyl acetate so as to obtain the white crystal Na-9-fluorenylmethoxycarbonyl-O-acetyl-L-serine product. The product synthesized by the method is an important raw material for synthesizing polypeptide drugs.
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Paragraph 0014; 0027
(2018/04/01)
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- Crystal structure of serine acetyl transferase from Brucella abortus and its complex with coenzyme A
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Brucella abortus is the major cause of premature foetal abortion in cattle, can be transmitted from cattle to humans, and is considered a powerful biological weapon. De novo cysteine biosynthesis is one of the essential pathways reported in bacteria, protozoa, and plants. Serine acetyltransferase (SAT) initiates this reaction by catalyzing the formation of O-acetylserine (OAS) using l-serine and acetyl coenzyme A as substrates. Here we report kinetic and crystallographic studies of this enzyme from B. abortus. The kinetic studies indicate that cysteine competitively inhibits the binding of serine to B. abortus SAT (BaSAT) and noncompetitively inhibits the binding of acetyl coenzyme A. The crystal structures of BaSAT in its apo state and in complex with coenzyme A (CoA) were determined to 1.96 ? and 1.87 ? resolution, respectively. BaSAT was observed as a trimer in a size exclusion column; however, it was seen as a hexamer in dynamic light scattering (DLS) studies and in the crystal structure, indicating it may exist in both states. The complex structure shows coenzyme A bound to the C-terminal region, making mostly hydrophobic contacts from the center of the active site extending up to the surface of the protein. There is no conformational difference in the enzyme between the apo and the complexed states, indicating lock and key binding and the absence of an induced fit mechanism.
- Kumar, Sudhir,Kumar, Nitesh,Alam, Neelima,Gourinath, Samudrala
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p. 1741 - 1748
(2014/08/18)
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- Molecular and biochemical characterisation of a serine acetyltransferase of onion, Allium cepa (L.)
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We have previously cloned a cDNA, designated SAT1, corresponding to a gene coding for a serine acetyltransferase (SAT) from onion (Allium cepa L.). The SAT1 locus was mapped to chromosome 7 of onion using a single-stranded conformation polymorphism (SSCP) in the 3′ UTR of the gene. Northern analysis has demonstrated that expression of the SAT1 gene is induced in leaf tissue in response to low S-supply. Phylogenetic analysis has placed SAT1 in a strongly supported group (100% bootstrap) that comprises sequences that have been characterised biochemically, including Allium tuberosum, Spinacea oleracea, Glycine max, Citrullus vulgaris, and SAT5 (AT5g56760) of Arabidopsis thaliana. This group can be divided further with the SAT1 of A. cepa sequence grouping strongly with the A. tuberosum sequence. Translation of SAT1 from onion generates a protein of 289 amino acids with a calculated molecular mass of 30,573 Da and pI of 6.52. The conserved G277 and H282 residues that have been identified as critical for l-cysteine inhibition are observed at G272 and H277. SAT1 has been cloned into the pGEX plasmid, expressed in E. coli and SAT activity of the recombinant enzyme has been measured as acetyl-CoA hydrolysis detected at 232 nm. A Km of 0.72 mM was determined for l-serine as substrate, a Km of 92 μM was calculated with acetyl-CoA as substrate, and an inhibition curve for l-cysteine generated an IC50 value of 3.1 μM. Antibodies raised against the recombinant SAT1 protein recognised a protein of ca. 33 kDa in whole leaf onion extracts. These properties of the SAT1 enzyme from onion are compared with other SAT enzymes characterised from closely related species.
- McManus, Michael T.,Leung, Susanna,Lambert, Anya,Scott, Richard W.,Pither-Joyce, Meeghan,Chen, Balance,McCallum, John
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p. 1407 - 1416
(2007/10/03)
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- Reaction of trichloroethylene oxide with proteins and DNA: Instability of adducts and modulation of functions
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Trichloroethylene (TCE) shows several types of toxicities, some of which may be the result of bioactivation. Oxidation by P450s yields the electrophile TCE oxide. We previously analyzed N6-acyllysine adducts formed from the reaction of TCE oxide with proteins [Cai, H., and Guengerich, F. P. (2000) Chem. Res. Toxicol. 13, 327-335]; however, we had been unable to measure ester adducts under the prolonged conditions of proteolysis and derivatization. Protein amino acid adducts were directly observed by mass spectrometry during the reaction of TCE oxide with the model polypeptides insulin and adrenocorticotropic hormone (ACTH, residues 1-24). The majority (80%) of the protein adducts were unstable under physiological conditions and had a collective t1/2 of ～1 h, suggesting that they are ester type adducts formed from reactions of Cys, Ser, Tyr, or Thr residues with intermediates formed in TCE oxide hydrolysis. Synthetic O-acetyl-L-Ser and O-acetyl-L-Tyr had half-lives of 1 h and 10 min at pH 8.0, respectively, similar to the stabilities of the protein adducts. The effects of TCE oxide adduct formation on catalytic activities were examined with five model enzymes. No recovery of catalytic activity was observed during the reaction of TCE oxide with two model enzymes for which the literature suggests roles of a Lys, rabbit muscle aldolase and glucose-6-phosphate dehydrogenase. However, in the cases of papain (essential Cys residue in the active site), α-chymotrypsin (critical Ser residue), and D-amino acid oxidase (essential Cys and Tyr residues), time-dependent recoveries of enzyme activity were observed following reaction with TCE oxide or either of two model nucleophiles (dichloroacetyl chloride and acetic formic anhydride), paralleling the kinetics of removal of adducts from insulin and ACTH. Formation of adducts (～2%) was detected in the direct reaction of TCE oxide with 2′-deoxyguanosine, but not with the other three nucleosides found in DNA. During the reaction of TCE oxide with a synthetic 8-mer oligonucleotide, formation of adducts was observed by mass spectrometry. However, the adducts had a t1/2 of 30 min at pH 8.5. These results indicate the transient nature of the adducts formed from the reaction of TCE oxide with macromolecules and their biological effects.
- Cai, Hongliang,Peter Guengerich
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