Insect multimeric G-quadruplexes fold into antiparallel structures of different compactness and stability in K+ and Na+ solutions.

Human telomere sequences (TTAGGG)n fold into G-quadruplexes with different conformations in K+ and Na+ solutions, which are highlighted for their potential as antitumor drug targets. Moreover, human multimeric G-quadruplexes have been broadly studied potentially for screening ligands with higher selectivity than monomeric G-quadruplexes. Most insects have telomeres consisting of pentanucleotide (TTAGG) repeats, which fold into an antiparallel structured G-quadruplex with a two-layer G-planar in a K+ solution. However, the structure of insect telomeric G-quadruplexes in Na+ solutions and their higher-order structures have not been explored. The quinoline derivative BMPQ-1 has been reported to bind human multimeric G-quadruplex. This study compared the stability and compactness of insect monomeric and multimeric G-quadruplex structures in K+ and Na+ solutions and further validated the interaction between BMPQ-1 and insect multimeric G-quadruplexes. Circular dichroism (CD) spectral scanning analysis revealed that although the insect telomeric G-quadruplex folds into an antiparallel structure in both K+ and Na+ solutions, all the insect telomeric G-quadruplexes are more stable in Na+ solutions. Fluorescence resonance energy transfer (FRET) analysis indicated insect telomeric G-quadruplexes have a more compact structure in Na+ solutions. BMPQ-1 exhibited higher selectivity for insect multimeric G-quadruplex Bom37 than monomeric G-quadruplex Bom17, and had a different binding pattern to Bom37 G-quadruplex in K+ and Na+ solutions. Finally, BMPQ-1 was found to have a significant inhibitory effect on the proliferation of pest cells. This study contributes to our comprehensive understanding of insect telomeric G-quadruplexes.

Effects of Molecular Crowding on the Structure, Stability, and Interaction with Ligands of G-quadruplexes.

G-quadruplexes (G4s) are widely found in cells and have significant biological functions, which makes them a target for screening antitumor and antiviral drugs. Most of the previous research on G4s has been conducted mainly in diluted solutions. However, cells are filled with organelles and many biomolecules, resulting in a constant state of a crowded molecular environment. The conformation and stability of some G4s were found to change significantly in the molecularly crowded environment, and interactions with ligands were disturbed to some extent. The structure of the G4s and their biological functions are correlated, and the effect of the molecularly crowded environment on G4 conformational transitions and interactions with ligands should be considered in drug design targeting G4s. This review discusses the changes in the conformation and stability of G4s in a physiological environment. Moreover, the mechanism of action of the molecularly crowded environment affecting the G4 has been further reviewed based on previous studies. Furthermore, current challenges and future research directions are put forward. This review has implications for the design of drugs targeting G4s.

Molecular crowding promotes the aggregation of parallel structured G-quadruplexes.

G-quadruplexes are widely distributed in cells and are usually essential in mediating biological processes. The intracellular environment is often in a state of molecular crowding, and the current research considerably focuses on the effect of molecular crowding on the conformation of telomeric G-quadruplexes. However, G-quadruplex-forming oligonucleotides are primarily located in the promoter region of the proto-oncogene and on mRNA inside the cell and are reported to fold into parallel structures. Thus, studying the interaction mechanism between ligands and parallel structured G-quadruplexes under crowding conditions is crucial for the design of drugs targeting G-quadruplexes. In our study, molecular crowding was simulated through polyethylene glycol with an average molecular weight of 200 (PEG200) to investigate the parallel structure of the canonical G-quadruplexes c-KIT1, c-MYC, and 32KRAS and their interactions with ligands. Circular dichroism (CD) spectral scanning, fluorescence resonance energy transfer (FRET), and native polyacrylamide gel electrophoresis (PAGE) analysis revealed that molecular crowding failed to induce oligonucleotides to form parallel G-quadruplex structures in the explored model sequences while induced telomeric G-rich sequences to form antiparallel G-quadruplexes in solution without K+. Molecular crowding did not induce changes in their parallel structures but promoted the formation of G-quadruplex aggregates. Moreover, to some extent, molecular crowding also induced a looser structure of the monomer G-quadruplexes. Further studies showed that molecular crowding did not alter the binding stoichiometry of the ligand 3,11-difluoro-6,8,13-trimethyl-8H-quino [4,3,2-kl] acridinium methosulfate (RHPS4) to c-KIT1, while it inhibited its interaction with parallel structured G-quadruplexes. This work provides new insights into developing anticancer drugs targeting parallel structured G-quadruplexes.

Highly Efficient Biotransformation and Production of Selenium Nanoparticles and Polysaccharides Using Potential Probiotic Bacillus subtilis T5

Selenium is an essential microelement required for human health. The biotransformation of selenium nanoparticles has attracted increasing attention in recent years. However, little of the literature has investigated the comprehensive evaluation of the strains for practical application and the effect on the functional properties in the existence of Se. The present study showed the selenite reduction strain Bacillus subtilis T5 (up to 200 mM), which could produce high yields of selenium polysaccharides and selenium nanoparticles in an economical and feasible manner. Biosynthesized selenium nanoparticles by B. subtilis T5 were characterized systematically using UV-vis spectroscopy, FTIR, Zeta Potential, DLS, and SEM techniques. The biosynthesized SeNPs exhibited high stability with small particle sizes. B. subtilis T5 also possessed a tolerance to acidic pH and bile salts, high aggregation, negative hemolytic, and superior antioxidant activity, which showed excellent probiotic potential and can be recommended as a potential candidate for the selenium biopharmaceuticals industry. Remarkably, B. subtilis T5 showed that the activity of α-amylase was enhanced with selenite treatment to 8.12 U/mL, 2.72-fold more than the control. The genus Bacillus was first reported to produce both selenium polysaccharides with extremely high Se-content (2.302 g/kg) and significantly enhance the activity to promote α-amylase with selenium treatment. Overall, B. subtilis T5 showed potential as a bio-factory for the biosynthesized SeNPs and organ selenium (selenium polysaccharide), providing an appealing perspective for the biopharmaceutical industry.

RHPS4 shifted the conformation ensemble equilibrium of Tel24 by preferentially stabilizing the (3 + 1) hybrid-2 conformation.

Telomeric G-quadruplexes have been a promising target for developing antitumor drugs with fewer side effects. The intracellular environment is usually in a state of molecular crowding. Studying the interaction mechanism among ligands and telomeric G-quadruplexes under crowded conditions is important for designing drugs that target telomeric G-quadruplexes. In the present study, the telomeric G-quadruplex Tel24 (TTAGGG)4 was found to fold into a conformational ensemble of parallel and (3 + 1) hybrid-2 conformations in solution with molecular crowding conditions created by PEG200. G-quadruplex-ligand 3,11-difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl] acridinium methosulfate (RHPS4) preferentially stabilized the (3 + 1) hybrid-2 conformation and shifted the conformational ensemble equilibrium of Tel24 towards the hybrid conformation. We also found that the (3 + 1) hybrid-2 conformation of Tel24 was more likely to form as compared to the parallel conformation in the conformational ensemble of Tel24. Overall, this study provides new insights into the conformation of telomere G-quadruplexes and their interactions with ligands in a physiological environment.