RESUMEN
Mycobacterium tuberculosis (Mtb), as a typical intracellular pathogen, possesses several putative restriction-modification (R-M) systems, which restrict exogenous DNA's entry, such as bacterial phage infection. Here, we investigate Rv2528c, a putative Mrr-like type IV restriction endonuclease (REase) from Mtb H37Rv, which is predicted to degrade methylated DNA that contains m6A, m5C, etc. Rv2528c shows significant cytotoxicity after being expressed in Escherichia coli BL21(DE3)pLysS strain. The Terminal deoxynucleotidyl transferase dUTP Nick-End Labeling (TUNEL) assay indicates that Rv2528c cleaves genomic DNA in vivo. The plasmid transformation efficiency of BL21(DE3)pLysS strain harboring Rv2528c gene was obviously decreased after plasmids were in vitro methylated by commercial DNA methyltransferases such as M.EcoGII, M.HhaI, etc. These results are consistent with the characteristics of type IV REases. The in vitro DNA cleavage condition and the consensus cleavage/recognition site of Rv2528c still remain unclear, similar to that of most Mrr-family proteins. The possible reasons mentioned above and the potential role of Rv2528c for Mtb were discussed.
RESUMEN
Toxin-antitoxin (TA) systems are the major mechanism for persister formation in Mycobacterium tuberculosis (Mtb). Previous studies found that HigBA2 (Rv2022c-Rv2021c), a predicted type II TA system of Mtb, could be activated for transcription in response to multiple stresses such as anti-tuberculosis drugs, nutrient starvation, endure hypoxia, acidic pH, etc. In this study, we determined the binding site of HigA2 (Rv2021c), which is located in the coding region of the upstream gene higB2 (Rv2022c), and the conserved recognition motif of HigA2 was characterized via oligonucleotide mutation. Eight binding sites of HigA2 were further found in the Mtb genome according to the conserved motif. RT-PCR showed that HigA2 can regulate the transcription level of all eight of these genes and three adjacent downstream genes. DNA pull-down experiments showed that twelve functional regulators sense external regulatory signals and may regulate the transcription of the HigBA2 system. Of these, Rv0903c, Rv0744c, Rv0474, Rv3124, Rv2603c, and Rv3583c may be involved in the regulation of external stress signals. In general, we identified the downstream target genes and possible upstream regulatory genes of HigA2, which paved the way for the illustration of the persistence establishment mechanism in Mtb.
RESUMEN
A polymer monolithic column was prepared in a syringe by using [2-(acryloyloxy) ethyl] trimethyl ammonium chloride (DAC) as a monomer and ethylene glycol dimethacrylate (EDMA) as a crosslinker. The obtained monolith was developed as a solid-phase extraction sorbent and used with high performance liquid chromatography (HPLC) for the analysis of three benzodiazepines (BZDs) including bromazepam (BRZ), lorazepam (LRZ) and diazepam (DZP) in urine. The effects of reaction time and the solid-phase extraction conditions (washing solution, elution solvent and volume) on the extraction efficiencies of the three BZDs were investigated. The monolithic column was successfully prepared within 4 h, and it offered 100% adsorption efficiency for the three BZDs. The urine sample (4 mL) was loaded on the monolith, washed with 4 mL of H2O, and eluted with 1 mL of ethyl acetate. Under the optimized conditions, the linear ranges were 4.0-1000 ng/mL for the three BZDs, with correlation coefficients (r) of 0.999. The limits of detection (S/N=3) and limits of quantification (S/N=10) of the three BZDs were in the range of 1.0-1.2 ng/mL and 3.3-4.0 ng/mL, respectively. The recoveries at three spiked levels (10, 25 and 50 ng/mL) of the three BZDs ranged from 81.4% to 102%, with intra-day and inter-day relative standard deviations (n=3) of 1.2%-4.5% and 2.5%-8.3%. The polymer monolithic column provided effective purification for the three BZDs in urine and the enrichment factor was 12-15. This polymer monolithic adsorbent has the advantages of easy preparation and high extraction efficiency. It is successfully applied to the determination of the three BZDs in urine samples.