Molecular mechanisms of ligand-mediated attenuation of DNA binding by MarR family transcriptional regulators

Bacteria and archaea encode members of the large multiple antibiotic resistance regulator (MarR) family of transcriptional regulators. Generally, MarR homologs regulate activity of genes involved in antibiotic resistance, stress responses, virulence or catabolism of aromatic compounds. They constitute a diverse group of transcriptional regulators that includes both repressors and activators, and the conventional mode of regulation entails a genetic locus in which the MarR homolog and a gene under its regulation are encoded divergently; binding of the MarR homolog to the intergenic region typically represses transcription of both genes, while binding of a specific ligand to the transcription factor results in attenuated DNA binding and hence activated gene expression. For many homologs, the natural ligand is unknown. Crystal structures reveal a common architecture with a characteristic winged helix domain for DNA binding, and recent structural information of homologs solved both in the absence and presence of their respective ligands, as well as biochemical data, is finally converging to illuminate the mechanisms by which ligand-binding causes attenuated DNA binding. As MarR homologs regulate pathways that are critical to bacterial physiology, including virulence, a molecular understanding of mechanisms by which ligands affect a regulation of gene activity is essential. Specifying the position of ligand-binding pockets further has the potential to aid in identifying the ligands for MarR homologs for which the ligand remains unknown. © The Author (2010)

Synthesis, Characterization, and Biological Studies of a Piperidinyl Appended Dipicolylamine Ligand and Its Rhenium Tricarbonyl Complex as Potential Therapeutic Agents for Human Breast Cancer

© 2016 Amali Subasinghe et al. A novel ligand bearing a central piperidinyl sulfonamide group, N(SO2pip)dpa, and its corresponding Re tricarbonyl complex, [Re(CO)3(N(SO2pip)dpa)]+, have been synthesized in good yield. The methylene CH2 signal seen as a singlet (4.54 ppm) in a 1H NMR spectrum of the ligand in DMSO-d6 appears as two doublets (5.39, 5.01 ppm) in a spectrum of the [Re(CO)3(N(SO2pip)dpa)]+ complex and confirms the presence of magnetically nonequivalent protons upon coordination to Re. Structural results revealed that the Re-N bond lengths fall within the normal range establishing coordination of ligand to metal. The presence of intraligand π→π and n→π transitions is indicated by the absorption peaks around 200-250 nm in UV-visible spectra. Absorption peaks in UV-visible spectra around 300 nm for metal complexes were identified as MLCT transitions. The S-N stretch observed as a strong peak at 923 cm-1 for N(SO2pip)dpa appeared at a shorter frequency, at 830 cm-1 in an FTIR spectrum of the [Re(CO)3(N(SO2pip)dpa)]+. The intense fluorescence displayed by the N(SO2pip)dpa ligand has quenched upon coordination to Re. Relatively low IC50 values given by human breast cancer cells, MCF-7, (N(SO2pip)dpa = 139 μM, [Re(CO)3(N(SO2pip)dpa)]+ = 360 μM) indicate that N(SO2pip)dpa and [Re(CO)3(N(SO2pip)dpa)]+ are promising novel compounds that can be further investigated on their usage as potential anticancer agents

Synthesis and Characterization of Novel Diethylenetriamine Based Sulfonamide Ligands and Their Bidentate Platinum(II) Complexes Toward Anticancer Drug Leads

Diethylenetriamine (dienH) is one of the most biologically compatible chelate frameworks. Its hydrophilic amine moiety was functionalized via N-sulfonylation with sulfonyl chloride to produce two novel ligands; N(SO2)(bzd)dienH (L1) and N(SO2)(4-Mebip)dienH (L2) and two reported ligands; N(SO2)(1-nap)dienH (L3) and N(SO2)(2-nap)dienH (L4). Treatment of cis-Pt(DMSO)2Cl2with L1, L2, L3 and L4 afforded four novel neutral complexes [Pt(N(SO2)(bzd)dienH)Cl2] (C1), [Pt(N(SO2)(4-Mebip)dienH)Cl2] (C2), [Pt(N(SO2)(1-nap)dienH)Cl2] (C3) and [Pt(N(SO2)(2-nap)dienH)Cl2] (C4) respectively. All synthesized compounds were characterized by 1H NMR, UV-Vis, FTIR and fluorescence spectroscopy. Aliphatic diethylenetriamine protons of the ligands appeared in the 3.00 -2.30 ppm region in 1H NMR spectra recorded in DMSO-d6. Upon complexation, the appearance of two broad NH peaks between 5.00 -7.00 ppm region and another broad peak between 7.00-8.00 ppm confirmed the bidentatedenticity of the ligands vs tridentate. The formation of metal complexes was further supported by FTIR spectra in which the S-N stretching band for the metal complexes appears at lower wavenumbers compared to that of the corresponding free ligands. Emission spectra were recorded in methanol and intense fluorescence properties were observed in the 331-364 nm range for the ligands, whereas the corresponding Pt complexes showed quenched fluorescence. In vitro cytotoxic effects were investigatedusing sulforhodamine B assay, where L2 (< 10 μg/mL) demonstrated increased levels of cytotoxicity followed by C2 (< 25 μg/mL) and C4 (< 50 μg/mL) to non-small cell lung cancer cells in dose and time-dependent manner, with less or no cytotoxic effects to normal lung cells tested. Among the compounds tested, C1 and C3 displayed comparatively lower but more potent cytotoxic effects on lung cancer cells. Notably, these compounds did not exhibit any toxicity towards normal cells. Thus, they hold promise as lead compounds for the development of chemotherapeutic agents targeting lung cancer. Keywords: Platinum, Sulfonamide, Biphenyl, Benzodioxan, aphthalen

Synthesis, Characterization and Remarkable Anticancer Activity of Rhenium Complexes Containing Biphenyl Appended NNN Donor Sulfonamide Ligands

Neutral and cationic rhenium complexes provide both hydrophilic as well as hydrophobic properties due to the robustness of the tridentate ligand system of biphenyl appended dipicolylamine (N(SO2bip)dpa) and diethylenetriamine (N(SO2bip)dienH) coordinated to the [Re(CO)3]+ core, hold immense potential for the development of metal based anticancer drugs. This was achieved by the synthesis of two ligands (L1: N(SO2bip)dpa and L2: (N(SO2bip)dienH) and their corresponding Re complexes (C1: [Re(CO)3(N(SO2bip)dpa)]PF6 and C2: [Re(CO)3(N(SO2bip)dien)] in good yield and high purity. All four compounds were characterized by 1H NMR, UV-Vis, FTIR spectroscopies and L1, also by single crystal X-ray diffraction. The methylene protons observed as a singlet at (4.59 ppm) in a 1H NMR spectrum of L1 appear as two doublets (5.66 and 4.65 ppm) in the spectrum of C1. The appearance of NH signals at 3.48, 5.17 and 6.69 ppm in the 1H NMR spectrum of C2 confirm the coordination of L2 with Re. The stretching vibration frequencies depicted by the S-N bond at 923 cm-1 for L1 appear towards lower frequencies (821 cm-1) in an FTIR spectrum of C1, while the S-N bond at 943 cm-1 for L2 appears towards higher frequencies (968 cm-1) in C2. In silico assessment of drug likeliness revealed zero violations demonstrating a high likeliness of the ligands to be successful as drug leads. All four compounds have shown very low IC50 values against non-small cell lung cancer cells (NCI-H292). Therefore, L1, C1, L2 and C2 are promising novel compounds that can be further investigated as potential anticancer agents. Keywords: Rhenium Tricarbonyl, Sulfonamide, Anticancer, Fluorescence

First Complete Cytochrome B Sequences and Molecular Taxonomy of Bat Species from Sri Lanka

The aim of our study was to address the research gap in the molecular taxonomy of Sri Lankan bats. The accurate identification of animals plays a major role in observing them in their natural environments and hence understanding possible disease-transmitting pathways from animals to humans. Being a tropical country, Sri Lanka has a high density of animals. There are 30 different species of bats described in Sri Lanka. Until now, the animals have been identified by observing their physical features. However, the visual identification of animals is not accurate because closely related animal groups may show similar physical features. During our study, we accurately differentiated five bat groups living in one of the largest caves in Sri Lanka by using a more sophisticated laboratory technique. Using molecular techniques, we were able to provide more accurate results than by the visual identification of the bats. The results from our study are stored in the NCBI database as a baseline for a repository of Sri Lankan bats. With the new sequence data provided here, we filled the gap concerning the molecular taxonomy of bat species of the entire region and we contributed to the future conservation and systematic studies of these mammalsThis is the first report on the molecular identification and phylogeny of the Rousettus leschenaultii Desmarest, 1810, Rhinolophus rouxii Temminck, 1835, Hipposideros speoris Schneider, 1800, Hipposideros lankadiva Kelaart, 1850, and Miniopterus fuliginosus Kuhl, 1817, bat species in Sri Lanka, inferred from analyses by mitochondrially encoded cytochrome b gene sequences. Recent research has indicated that bats show enormous cryptic genetic diversity. Moreover, even within the same species, the acoustic properties of echolocation calls and morphological features such as fur color could vary in different populations. Therefore, we have used molecular taxonomy for the accurate identification of five bat species recorded in one of the largest cave populations in Sri Lanka. The bats were caught using a hand net, and saliva samples were collected non-invasively from each bat by using a sterile oral swab. Nucleic acids were extracted from the oral swab samples, and mitochondrial DNA was amplified by using primers targeting the mitochondrially encoded cytochrome b gene. This study reports the first molecular evidence for the identification of five bat species in Sri Lanka. Our findings will contribute to future conservation and systematic studies of bats in Sri Lanka. This study will also provide the basis for a genetic database of Sri Lankan bats which will contribute significantly to the investigation of potentially zoonotic bat viruses.Peer Reviewe

Synthesis, Characterization, and BSA-Binding Studies of Novel Sulfonated Zinc-Triazine Complexes

Four Zn(II) complexes containing a pyridyl triazine core (L1 = 3-(2-pyridyl)-5,6-di(2-furyl)-1,2,4-triazine-5′,5″-disulfonic acid disodium salt and L2 = 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4′,4″-disulfonic acid sodium salt) were synthesized, and their chemical formulas were finalized as [Zn(L1)Cl2]·5H2O·ZnCl2 (1), [Zn(L1)2Cl2]·4H2O·2CH3OH (2), [Zn(L2)Cl2]·3H2O·CH3OH (3), and [Zn(L2)2Cl2] (4). The synthesized complexes are water soluble, making them good candidates for biological applications. All four complexes have been characterized by elemental analysis and 1H NMR, IR, and UV-Vis spectroscopy. The IR stretching frequency of N=N and C=N bonds of complexes 1–4 have shifted to lower frequencies in comparison with free ligands, and a bathochromic shift was observed in UV-Vis spectra of all four complexes. The binding studies of ligands and complexes 1–4 with bovine serum albumin (BSA) resulted binding constants (Kb) of 3.09 × 104 M−1, 12.30 × 104 M−1, and 16.84 × 104 M−1 for ferene, complex 1, and complex 2, respectively, indicating potent serum distribution via albumins

Synthesis, Characterization, and Biological Studies of a Piperidinyl Appended Dipicolylamine Ligand and Its Rhenium Tricarbonyl Complex as Potential Therapeutic Agents for Human Breast Cancer

A novel ligand bearing a central piperidinyl sulfonamide group, N(SO2pip)dpa, and its corresponding Re tricarbonyl complex, [Re(CO)3(N(SO2pip)dpa)]+, have been synthesized in good yield. The methylene CH2 signal seen as a singlet (4.54 ppm) in a 1H NMR spectrum of the ligand in DMSO-d6 appears as two doublets (5.39, 5.01 ppm) in a spectrum of the [Re(CO)3(N(SO2pip)dpa)]+ complex and confirms the presence of magnetically nonequivalent protons upon coordination to Re. Structural results revealed that the Re–N bond lengths fall within the normal range establishing coordination of ligand to metal. The presence of intraligand π→π⁎ and n→π⁎ transitions is indicated by the absorption peaks around 200–250 nm in UV-visible spectra. Absorption peaks in UV-visible spectra around 300 nm for metal complexes were identified as MLCT transitions. The S–N stretch observed as a strong peak at 923 cm−1 for N(SO2pip)dpa appeared at a shorter frequency, at 830 cm−1 in an FTIR spectrum of the [Re(CO)3(N(SO2pip)dpa)]+. The intense fluorescence displayed by the N(SO2pip)dpa ligand has quenched upon coordination to Re. Relatively low IC50 values given by human breast cancer cells, MCF-7, (N(SO2pip)dpa = 139 μM, [Re(CO)3(N(SO2pip)dpa)]+ = 360 μM) indicate that N(SO2pip)dpa and [Re(CO)3(N(SO2pip)dpa)]+ are promising novel compounds that can be further investigated on their usage as potential anticancer agents

Structure Guided Design of Xanthomonas oryzae pv. oryzae Topoisomerase I Inhibitors

Topoisomerase inhibitors initiate the cell killing process by either stabilizing or increasing the amount of the covalent complex formed between the enzyme and cleaved DNA. [...

Effects of Habitat Change on the Web Characteristics and Fitness of the Giant Wood Spider (Nephila pilipes) in Sri Lanka

We compare web properties and fitness of the Giant wood spider Nephila pilpes within and outside its natural rainforest habitat in Sri Lanka. The nonforest habitats comprised rural home gardens and plantations. We hypothesize that marked differences would be evident between the two habitats in (i) web properties and (ii) fitness of the female spiders. Web architectural and silk thread properties were measured in 25 webs of adult female spiders in each of the two habitats, while female abdomen size was used as the proxy for fitness. Findings support both hypotheses. The nonforest webs were more closely knit (smaller mesh spaces) and the hub was placed at higher position on the web than that in the forest webs both altering prey capture efficiency. Also, females in nonforest habitats were significantly smaller than those in the forest, indicating lowered fitness. The disparities in web characteristics and fitness are impressive given that the forest and nonforest habitats are located in close proximity, suggesting that rainforest orbweaver spiders such as Nephila pilpes may suffer population declines if the extents of natural forest continue to shrink