Sequence specific hydrogen bond of DNA with denaturants affects its stability: Spectroscopic and simulation studies

Investigation of Aggregation and Disaggregation of Self-Assembling Nano-Sized Clusters Consisting of Individual Iron Oxide Nanoparticles upon Interaction with HEWL Protein Molecules

In this paper, iron oxide nanoparticles coated with trisodium citrate were obtained. Nanoparticles self-assembling stable clusters were ~10 and 50-80 nm in size, consisting of NPs 3 nm in size. The stability was controlled by using multi-angle dynamic light scattering and the zeta potential, which was -32 ± 2 mV. Clusters from TSC-IONPs can be destroyed when interacting with a hen egg-white lysozyme. After the destruction of the nanoparticles and proteins, aggregates are formed quickly, within 5-10 min. Their sizes depend on the concentration of the lysozyme and nanoparticles and can reach micron sizes. It is shown that individual protein molecules can be isolated from the formed aggregates under shaking. Such aggregation was observed by several methods: multi-angle dynamic light scattering, optical absorption, fluorescence spectroscopy, TEM, and optical microscopy. It is important to note that the concentrations of NPs at which the protein aggregation took place were also toxic to cells. There was a sharp decrease in the survival of mouse fibroblasts (Fe concentration ~75-100 μM), while the ratio of apoptotic to all dead cells increased. Additionally, at low concentrations of NPs, an increase in cell size was observed.

Time-Dependent DNA Origami Denaturation by Guanidinium Chloride, Guanidinium Sulfate, and Guanidinium Thiocyanate

Guanidinium (Gdm) undergoes interactions with both hydrophilic and hydrophobic groups and, thus, is a highly potent denaturant of biomolecular structure. However, our molecular understanding of the interaction of Gdm with proteins and DNA is still rather limited. Here, we investigated the denaturation of DNA origami nanostructures by three Gdm salts, i.e., guanidinium chloride (GdmCl), guanidinium sulfate (Gdm₂SO₄), and guanidinium thiocyanate (GdmSCN), at different temperatures and in dependence of incubation time. Using DNA origami nanostructures as sensors that translate small molecular transitions into nanostructural changes, the denaturing effects of the Gdm salts were directly visualized by atomic force microscopy. GdmSCN was the most potent DNA denaturant, which caused complete DNA origami denaturation at 50 °C already at a concentration of 2 M. Under such harsh conditions, denaturation occurred within the first 15 min of Gdm exposure, whereas much slower kinetics were observed for the more weakly denaturing salt Gdm₂SO₄ at 25 °C. Lastly, we observed a novel non-monotonous temperature dependence of DNA origami denaturation in Gdm₂SO₄ with the fraction of intact nanostructures having an intermediate minimum at about 40 °C. Our results, thus, provide further insights into the highly complex Gdm–DNA interaction and underscore the importance of the counteranion species.

Contrasting Effect of Salts on the Binding of Antimalarial Drug Hydroxychloroquine with Different Sequences of Duplex DNA

Hydroxychloroquine (HCQ) is an important antimalarial drug which functions plausibly by targeting the DNA of parasites. Salts play a crucial role in the functionality of various biological processes. Hence, the effect of salts (NaCl and MgCl₂) on the binding of HCQ with AT- and CG-DNAs as well as the binding-induced stability of both sequences of DNAs have been investigated using the spectroscopic and molecular dynamics (MD) simulation methods. It has been found that the effect of salts on the binding of HCQ is highly sensitive to the nature of ions as well as DNA sequences. The effect of ions is opposite for the binding of AT- and CG-DNAs as the presence of Mg²⁺ ions enhances the binding of HCQ with AT-DNA, whereas the binding of HCQ with CG-DNA gets decreased on the addition of both ions. Similarly, the presence of Mg²⁺ enhances the stabilization of HCQ-bound AT-DNA, whereas the effect is opposite for the CG-DNA in the presence of both the ions. The MD simulation study suggests that the hydration states of both ions are different and they interact differently in the minor and major grooves of both the sequences of DNA which may be one of the reasons for the different binding of HCQ with these two sequences of DNA in the presence of salts. The information about the effect of salts on the binding of HCQ with DNAs in a sequence-specific manner may be useful in understanding the mechanism of the action and toxicity effect of HCQ against malaria.

Adenine oligomer directed synthesis of chiral gold nanoparticles

Precise control of morphology and optical response of 3-dimensional chiral nanoparticles remain as a significant challenge. This work demonstrates chiral gold nanoparticle synthesis using single-stranded oligonucleotide as a chiral shape modifier. The homo-oligonucleotide composed of Adenine nucleobase specifically show a distinct chirality development with a dissymmetric factor up to g ~ 0.04 at visible wavelength, whereas other nucleobases show no development of chirality. The synthesized nanoparticle shows a counter-clockwise rotation of generated chiral arms with approximately 200 nm edge length. The molecular dynamics and density functional theory simulations reveal that Adenine shows the highest enantioselective interaction with Au(321)R/S facet in terms of binding orientation and affinity. This is attributed to the formation of sequence-specific intra-strand hydrogen bonding between nucleobases. We also found that different sequence programming of Adenine-and Cytosine-based oligomers result in chiral gold nanoparticles' morphological and optical change. These results extend our understanding of the biomolecule-directed synthesis of chiral gold nanoparticles to sequence programmable deoxyribonucleic acid and provides a foundation for programmable synthesis of chiral gold nanoparticles.

Anion-specific structure and stability of guanidinium-bound DNA origami

While the folding of DNA into rationally designed DNA origami nanostructures has been studied extensively with the aim of increasing structural diversity and introducing functionality, the fundamental physical and chemical properties of these nanostructures remain largely elusive. Here, we investigate the correlation between atomistic, molecular, nanoscopic, and thermodynamic properties of DNA origami triangles. Using guanidinium (Gdm) as a DNA-stabilizing but potentially also denaturing cation, we explore the dependence of DNA origami stability on the identity of the accompanying anions. The statistical analyses of atomic force microscopy (AFM) images and circular dichroism (CD) spectra reveals that sulfate and chloride exert stabilizing and destabilizing effects, respectively, already below the global melting temperature of the DNA origami triangles. We identify structural transitions during thermal denaturation and show that heat capacity changes ΔC_p determine the temperature sensitivity of structural damage. The different hydration shells of the anions and their potential to form Gdm⁺ ion pairs in concentrated salt solutions modulate ΔC_p by altered wetting properties of hydrophobic DNA surface regions as shown by molecular dynamics simulations. The underlying structural changes on the molecular scale become amplified by the large number of structurally coupled DNA segments and thereby find nanoscopic correlations in AFM images.

DNA-assembled visible nanodandelions with explosive hydrogen-bond breakage achieving uniform intra-tumor distribution (UITD)-guided photothermal therapy

Photothermal therapy (PTT) has received increasing attention for treating tumors. However, a long-standing challenge in PTT is non-uniform distribution of photothermal agents (PAs) in tumor tissues, resulting in limited therapeutic efficiency. Herein, inspired by dandelions blowing away by the wind, we have designed a DNA-assembled visible GRS-DNA-CuS nanodandelion, which can achieve uniform intra-tumor distribution (UITD) of PAs, thus enhancing the photothermal therapeutic efficiency. GRS-DNA-CuS is featured by the formation of hydrogen bond between the core of single-strand DNA-modified Raman nanoprobes (GRS) and the shell of complementary single-strand DNA-modified CuS PAs. Under Raman imaging-guided 1st NIR irradiation, hydrogen bond in GRS-DNA-CuS is explosively broken, resulting in large-sized GRS-DNA-CuS (∼135 nm) be completely dissociated into GRS and ultra-small CuS PAs (∼12 nm) within 1 min. Such an explosive dissociation instantly enhances the local concentration of ultra-small CuS PAs and slightly rises intra-tumor temperature, thus increasing the diffusion coefficient of PAs and promoting their UITD. This UITD of CuS PAs enhances the photothermal anti-tumor effects. Three out of five tumors are completely eliminated under photoacoustic imaging-guided 2nd NIR irradiation. Overall, this study provides one UITD-guided PTT strategy for highly effective tumor treatment by exerting explosive breakage property of hydrogen bond, broadening the application scope of DNA-assembly technique in oncology field.

Groove Switching of Hydroxychloroquine Modulates the Efficacy of Binding and Induced Stability to DNA

Hydroxychloroquine (HCQ) is an important drug for the treatment of rheumatoid arthritis and malaria. HCQ targets specifically to nucleic acids for its action. However, the mechanism of HCQ binding and the effect of its binding on the stability of DNA are elusive. In this study, the binding mechanism of HCQ and the effect of binding on stability of different sequences of DNA have been investigated using spectroscopic and molecular dynamics (MD) simulation techniques. HCQ binds with all of the sequences of DNA and stabilizes them. However, binding efficacy of HCQ with DNA depends on its sequences as the binding constant is highest for pure guanine-cytosine (G-C) rich DNA and decreases with the increase of adenine-thymine (A-T) bases. HCQ prefers to interact with AT DNA through the minor groove whereas the major groove along with intercalation are the favorable binding mode in the case of GC DNA. The binding of HCQ in the major groove of GC DNA enhances the stacking between the bases compared to the case of AT DNA which leads to higher stability for GC DNA. It appears that the groove switching of HCQ is correlated with binding affinity as well as stability of different sequences of DNA.

Spectroscopic and Simulation Studies of the Sequence-Dependent DNA Destabilization by a Fungicide

The understanding of the structural change of DNA induced by fungicides is essential as the non-targeted action of fungicides causes genotoxicity, leading to several serious diseases such as cancer, behavioral change, and nausea. In this study, the binding of an important fungicide, namely, n-dodecylguanidine acetate (dodine), with B-DNA having different sequences of nucleobases and its effect on the structure of B-DNA has been investigated using spectroscopic and simulation methods. In general, the addition of dodine destabilizes DNA; however, the binding of dodine causing the destabilization of DNA is highly sequence dependent. In the case of adenine(A)-thymine(T)-based DNA, dodine intrudes into the minor groove of DNA and interacts with the A-T bases mainly through its hydrocarbon tail, which destabilizes the stacking interaction of the flanking bases. In contrast, the polar group of dodine interacts with guanine(G)-cytosine(C)-rich DNA, and the interaction is dynamic as it shuttles between the minor groove and terminal regions. The binding of dodine with G-C-rich DNA affects the stacking interaction of the terminal base regions specifically. This study reveals the base-specific binding mode of dodine, which causes destabilization of the duplex DNA.