Antagonistic control of a dual-input mammalian gene switch by food additives

Synthetic biology has significantly advanced the design of mammalian trigger-inducible transgene-control devices that are able to programme complex cellular behaviour. Fruit-based benzoate derivatives licensed as food additives, such as flavours (e.g. vanillate) and preservatives (e.g. benzoate), are a particularly attractive class of trigger compounds for orthogonal mammalian transgene control devices because of their innocuousness, physiological compatibility and simple oral administration. Capitalizing on the genetic componentry of the soil bacterium Comamonas testosteroni, which has evolved to catabolize a variety of aromatic compounds, we have designed different mammalian gene expression systems that could be induced and repressed by the food additives benzoate and vanillate. When implanting designer cells engineered for gene switch-driven expression of the human placental secreted alkaline phosphatase (SEAP) into mice, blood SEAP levels of treated animals directly correlated with a benzoate-enriched drinking programme. Additionally, the benzoate-/vanillate-responsive device was compatible with other transgene control systems and could be assembled into higher-order control networks providing expression dynamics reminiscent of a lap-timing stopwatch. Designer gene switches using licensed food additives as trigger compounds to achieve antagonistic dual-input expression profiles and provide novel control topologies and regulation dynamics may advance future gene- and cell-based therapies.     

Allosteric Communication between the Pyridoxal 5′-Phosphate (PLP) and Heme Sites in the H2S Generator Human Cystathionine β-Synthase

Human cystathionine β-synthase (CBS) is a unique pyridoxal 5′-phosphate (PLP)-dependent enzyme that has a regulatory heme cofactor. Previous studies have demonstrated the importance of Arg-266, a residue at the heme pocket end of α-helix 8, for communication between the heme and PLP sites. In this study, we have examined the role of the conserved Thr-257 and Thr-260 residues, located at the other end of α-helix 8 on the heme electronic environment and on activity. The mutations at the two positions destabilize PLP binding, leading to lower PLP content and ∼2- to ∼500-fold lower activity compared with the wild-type enzyme. Activity is unresponsive to PLP supplementation, consistent with the pyridoxine-nonresponsive phenotype of the T257M mutation in a homocystinuric patient. The H₂S-producing activities, also impacted by the mutations, show a different pattern of inhibition compared with the canonical transsulfuration reaction. Interestingly, the mutants exhibit contrasting sensitivities to the allosteric effector, S-adenosylmethionine (AdoMet); whereas T257M and T257I are inhibited, the other mutants are hyperactivated by AdoMet. All mutants showed an increased propensity of the ferrous heme to form an inactive species with a 424 nm Soret peak and exhibited significantly reduced enzyme activity in the ferrous and ferrous-CO states. Our results provide the first evidence for bidirectional transmission of information between the cofactor binding sites, suggest the additional involvement of this region in allosteric communication with the regulatory AdoMet-binding domain, and reveal the potential for independent modulation of the canonical transsulfuration versus H₂S-generating reactions catalyzed by CBS.     

Design and synthesis of diarylamines and diarylethers as cytotoxic antitumor agents

Based on a shared structural core of diarylamine in several known anticancer drugs as well as a new cytotoxic hit 6-chloro-2-(4-cyanophenyl)amino-3-nitropyridine (7), 30 diarylamines and diarylethers were designed, synthesized, and evaluated for cytotoxic activity against A549, KB, KB-vin, and DU145 human tumor cell lines (HTCL). Four new leads 11e, 12, 13a, and 13b were discovered with GI(50) values ranging from 0.33 to 3.45μM. Preliminary SAR results revealed that a diarylamine or diarylether could serve as an active structural core, meta-chloro and ortho-nitro groups on the A-ring (either pyridine or phenyl ring) were necessary and crucial for cytotoxic activity, and the para-substituents on the other phenyl ring (B-ring) were related to inhibitory selectivity for different tumor cells. In an investigation of potential biological targets of the new leads, high thoughput kinase screening discovered that new leads 11e, 12 and 13b especially inhibit Mer tyrosine kinase, a proto-oncogene associated with munerous tumor types, with IC(50) values of 2.2-3.0μM. Therefore, these findings provide a good starting point to optimize a new class of compounds as potential anticancer agents, particularly targeting Mer tyrosine kinase.     

Increased risk of lung cancer associated with a functionally impaired polymorphic variant of the human DNA glycosylase NEIL2

Human NEIL2, one of five oxidized base-specific DNA glycosylases, is unique in preferentially repairing oxidative damage in transcribed genes. Here we show that depletion of NEIL2 causes a 6-7-fold increase in spontaneous mutation frequency in the HPRT gene of the V79 Chinese hamster lung cell line. This prompted us to screen for NEIL2 variants in lung cancer patients' genomic DNA. We identified several polymorphic variants, among which R103Q and R257L were frequently observed in lung cancer patients. We then characterized these variants biochemically, and observed a modest decrease in DNA glycosylase activity relative to the wild type (WT) only with the R257L mutant protein. However, in reconstituted repair assays containing WT NEIL2 or its R257L and R103Q variants together with other DNA base excision repair (BER) proteins (PNKP, Polβ, Lig IIIα and XRCC1) or using NEIL2-FLAG immunocomplexes, an ~5-fold decrease in repair was observed with the R257L variant compared to WT or R103Q NEIL2, apparently due to the R257L mutant's lower affinity for other repair proteins, particularly Polβ. Notably, increased endogenous DNA damage was observed in NEIL2 variant (R257L)-expressing cells relative to WT cells. Taken together, our results suggest that the decreased DNA repair capacity of the R257L variant can induce mutations that lead to lung cancer development.     

Methylnaltrexone prevents morphine-induced kaolin intake in the rat

Opioids are frequently used analgesics, and emesis is a common opioid-induced adverse effect. Methylnaltrexone, a peripheral opioid antagonist, has the potential to block the undesired effects of opioids that are mediated by peripheral receptors while sparing the analgesic effect. We used a rat model of simulated emesis or pica to study if methylnaltrexone decreases morphine induced-kaolin consumption. We observed that after morphine administration, kaolin intake increased significantly compared to intake in the vehicle group, and the increase could be attenuated by ondansetron administration. Methylnaltrexone dose-dependently reduced kaolin ingestion induced by morphine. Morphine and methylnaltrexone did not significantly affect food intake and body weight in the experimental animals. Our data suggest that methylnaltrexone has therapeutic value in treating opioid-induced nausea and vomiting.     

Interaction between hesperetin and human serum albumin revealed by spectroscopic methods

Hesperetin (5,7,3'-trihydroxyl-4'-methoxyl-flavanone) is an important bioactive compound in Chinese traditional medicine and has multiple biological and pharmacological activities. The interaction of hesperetin with human serum albumin (HSA) has been investigated by UV absorption, fluorescence and Fourier transformed infrared spectrometry. Fluorescence results showed that one molecule of protein combined with one molecule of drug at the molar ratio of drug to HSA ranging from 0.3 to 7 and the binding affinity (K(A)) was 8.11x10(4) M(-1). The primary binding site was most likely located on subdomain IIA. The binding ability of the drug to protein decreased from pH 6.4 to 8.4 in the drug to protein molar ratio of 1. Combining the curve-fitting results of infrared amide I band in D2O and H2O phosphate buffers, the alterations of protein secondary structure after drug complexation were estimated. With increasing the drug concentration, the percentage of protein alpha-helix structure decreased gradually. The reduction of protein alpha-helix structure reached about 7-9% after the protein interacted with hesperetin in D2O and H2O buffer solution at pH 7.4 when the drug to protein molar ratio was 10. This indicated a partial unfolding of HSA in the presence of the drug. From the results of UV absorption, fluorescence and Fourier transformed infrared spectrometry, the binding mode was discussed. The main mechanism of protein fluorescence quenching was a static quenching process and the hydroxyl groups of the drug in its neutral part played an important role in the binding process.     

Purification and properties of the Escherichia coli nucleoside transporter NupG, a paradigm for a major facilitator transporter sub-family

NupG from Escherichia coli is the archetype of a family of nucleoside transporters found in several eubacterial groups and has distant homologues in eukaryotes, including man. To facilitate investigation of its molecular mechanism, we developed methods for expressing an oligohistidine-tagged form of NupG both at high levels (>20% of the inner membrane protein) in E. coli and in Xenopus laevis oocytes. In E. coli recombinant NupG transported purine (adenosine) and pyrimidine (uridine) nucleosides with apparent K(m) values of approximately 20-30 microM and transport was energized primarily by the membrane potential component of the proton motive force. Competition experiments in E. coli and measurements of uptake in oocytes confirmed that NupG was a broad-specificity transporter of purine and pyrimidine nucleosides. Importantly, using high-level expression in E. coli and magic-angle spinning cross-polarization solid-state nuclear magnetic resonance, we have for the first time been able directly to measure the binding of the permeant ([1'-(13)C]uridine) to the protein and to assess its relative mobility within the binding site, under non-energized conditions. Purification of over-expressed NupG to near homogeneity by metal chelate affinity chromatography, with retention of transport function in reconstitution assays, was also achieved. Fourier transform infrared and circular dichroism spectroscopy provided further evidence that the purified protein retained its 3D conformation and was predominantly alpha-helical in nature, consistent with a proposed structure containing 12 transmembrane helices. These findings open the way to elucidating the molecular mechanism of transport in this key family of membrane transporters.     

Oxalate production at different initial Pb²+ concentrations and the influence of oxalate during solid-state fermentation of straw with Phanerochaete chrysosporium

The production of oxalate at different initial Pb²⁺ concentrations during solid-state fermentation of straw with Phanerochaete chrysosporium was investigated. It was found that the maximal peak value of oxalate concentration (22.84 mM) was detected at the initial Pb²⁺ concentration of 200 mg kg⁻¹ dry straw, while the minimum (15.89 mM) at the concentration of 600 mg Pb²⁺ kg⁻¹ dry straw, and at moderate concentration of Pb²⁺ the capability of oxalic acid secretion was enhanced. In addition, it was also found that more oxalic acid accumulation went together with better Pb²⁺ passivation effect and higher manganese peroxidase (MnP) activity. The present findings will improve the understandings of the interactions of heavy metals with white-rot fungi and the role of oxalate in lignin degradation system, which could provide useful references for more efficient treatment of Pb-contaminated lignocellulosic waste.