Spectroscopic and molecular modeling methods to investigate the interaction between psycho-stimulant modafinil and calf thymus DNA using ethidium bromide as a fluorescence probe

Fluorescence Spectroscopy: A Useful Method to Explore the Interactions of Small Molecule Ligands with DNA Structures

Small molecule ligands-DNA interactions have recently received a lot of attention in the fields of life sciences, medicine, and chemical sciences. To decode these interactions, many strategies have been developed. DNA is the primary target for a wide range of drugs that may interact with DNA in particular or non-specific ways and impact its activities. Fluorescence spectroscopy is a highly advanced and non-invasive technology for measuring the concentrations of substrates and products or identifying characteristic processing states. Small molecule ligands-DNA interaction studies are beneficial not only in comprehending the method of interaction, but also in synthesizing DNA-targeted particular drugs. Several small compounds that bind to DNA are clinically established therapeutic medicines, while their specific mechanism of action is unknown. Figuring out their molecular recognizing patterns is the only way to construct innovative compounds that can target specific DNA sequences with strong affinities. This book chapter will mostly explore several fluorescence spectroscopic methodologies used to investigate interactions between small molecule ligands and DNA. In addition, we provide many approaches for determining a drug's binding mode with DNA. These strategies produce data that is both trustworthy and easy to comprehend. All of the knowledge gained by studying these fluorescence spectroscopies are supposed to lead to the development of more efficient new pharmaceuticals that might aid in the treatment of diseases.

Interaction of bifunctional peptide-carbazole complexes with DNA and antimicrobial activity

Two peptide-carbazole conjugates, CTAT and CNLS, were designed and synthesized using carbazole Schiff base to modify the cell membrane penetrating peptide TAT (47-57) and the nuclear localization peptide NLS at the N terminus. The interaction with ctDNA was investigated by multispectral and agarose gel electrophoresis. And the effects of CNLS and CTAT on the G-quadruplex structure were explored by circular dichroism titration experiments. The results show that both CTAT and CNLS interact with ctDNA in a minor groove binding manner. Both conjugates bind more tightly to DNA than the individual substances CIBA, TAT and NLS. In addition, CTAT and CNLS are capable of unfolding parallel G-quadruplex structures and are potential G-quadruplex unfolding agents. Finally, broth microdilution was performed to test the antimicrobial activity of the peptides. The results showed that CTAT and CNLS had a 4-fold increase in antimicrobial activity compared with the parent peptides TAT and NLS. They could exert antimicrobial activity by disrupting the integrity of cell membrane bilayer and binding to DNA, and could be used as novel antimicrobial peptides for the development of novel antimicrobial antibiotics.

Mechanisms of Surfactin from Bacillus subtilis SF1 against Fusarium foetens: A Novel Pathogen Inducing Potato Wilt

Fusarium wilt is a severe and worldwide disease in potato cultivation. In this study, Fusarium foetens was first identified as the pathogen of potato wilt. Bacillus subtilis SF1 has the potential for controlling potato wilt induced by F. foetens, resulting in a mycelium growth inhibition of 52.50 ± 2.59% in vitro and a significant decrease in incidence rate by 45.56% in vivo. This research highlighted the antifungal activity of surfactin from B. subtilis SF1 and attempted to reveal the unknown antifungal mechanisms. Surfactin inhibited F. foetens mycelium growth beyond the concentration of 20 μg/μL. Surfactin-treated mycelium appeared to have morphological malformation. Surfactin enhanced reduced glutathione production and caused the increase in values of the extracellular fluids in OD260 and OD280. Surfactin induced differential protein expression and changed the genes’ transcription levels. Surfactin binds to fungal DNA via groove-binding mode, with a binding constant of Kb 2.97 × 104 M−1. Moreover, B. subtilis SF1 harbored genes encoding plant-promoting determinants, making potato seedlings grow vigorously. The results will help provide a comprehensive understanding of the mechanisms of surfactin against filamentous fungi and the application of surfactin-producing microbial in the biocontrol of plant pathogenic fungi.

Efficient fluorescent recognition of ATP/GTP by a water-soluble bisquinolinium pyridine-2,6-dicarboxamide compound. Crystal structures, spectroscopic studies and interaction mode with DNA

The new dicationic pyridine-2,6-dicarboxamide-based compound 1 bearing two N-alkylquinolinium units was synthesized, structurally determined by single-crystal X-ray diffraction, and studied in-depth as a fluorescent receptor for nucleotides and inorganic phosphorylated anions in pure water. The addition of nucleotides to 1 at pH = 7.0 quenches its blue emission with a selective affinity towards adenosine 5'-triphosphate (ATP) and guanosine 5'-tripohosphate (GTP) over other nucleotides such CTP, UTP, ADP, AMP, dicarboxylates and inorganic anions. On the basis of the spectroscopic tools (1H, 31P NMR, UV-vis, fluorescence), MS measurements and DFT calculations, receptor 1 binds ATP with high affinity (log K = 5.04) through the simultaneous formation of strong hydrogen bonds and π-π interactions between the adenosine fragment and quinolinium ring with binding energy calculated in 8.7 kcal mol-1. High affinity for ATP/GTP is attributed to the high acidity of amides and preorganized rigid structure of 1. Receptor 1 is an order of magnitude more selective for ATP than GTP. An efficient photoinduced electron transfer quenching mechanism with simultaneous receptor-ATP complexation in both the excited and ground states is proposed. Additionally, multiple spectroscopic studies and molecular dynamics simulations showed that 1 can intercalate into DNA base pairs.

Understanding the binding behavior of Malathion with calf thymus DNA by spectroscopic, cell viability and molecular dynamics simulation techniques: binary and ternary systems comparison

The interaction between calf thymus DNA (ctDNA) and Malathion in the absence and presence of Histone 1 has been enquired by the means of spectroscopic, viscometry, molecular modeling, and cell viability assay techniques. Malathion is capable of quenching the fluorescence of ct DNA in the absence and presence of H1. The binding constants of Malathion-ctDNA complex in the absence of H1 have been calculated to be 6.62 × 10⁴, 4.31 × 10⁴ and 1.93 × 10⁴ M^-1 at 298, 303, and 308 K, respectively that revealed static quenching in complex formation. The observed negative values of enthalpy and entropy changes indicate that the main binding interaction forces were van der Waals force and hydrogen bonding. The binding constant between Malathion and single-stranded ctDNA (ss ctDNA) seemed to be much weaker than that of Malathion and double-stranded ctDNA (ds ctDNA). Furthermore, Malathion can induce detectable alterations in the CD spectrum of ctDNA, along with changes in its viscosity. In the presence of H1, fluorescence quenching of ctDNA-Malathion complex displays dynamic behavior and binding constants were perceived to be 1.66 × 10⁴, 2.93 × 10⁴ and 5.77 × 10⁴ M^-1 at 298, 303, and 308 K, respectively. The different of interaction behavior between ctDNA and Malathion in the absence and presence of H1 clearly revealed H1 role in the complex formation and forces change between ctDNA and Malathion. The positive values of enthalpy and entropy changes have suggested that binding process is primarily driven by hydrophobic interactions. The tendency to interact with ss ctDNA, reduced viscosity have designated that the Malathion bound to ctDNA in the presence of H1 is groove binding. The results of molecular docking and molecular dynamics simulation also confirmed potent interactions between Malathion and the macromolecules in the binary and ternary systems.Communicated by Ramaswamy H. Sarma.