The binding of a c-MYC promoter G-quadruplex to neurotransmitters: An analysis of G-quadruplex stabilization using DNA melting, fluorescence spectroscopy, surface-enhanced Raman scattering and molecular docking

The interactions of several neurotransmitter and neural hormone molecules with the c-MYC G-quadruplex DNA sequence were analyzed using a combination of spectroscopic and computational techniques. The interactions between indole, catecholamine, and amino acid neurotransmitters and DNA sequences could potentially add to the understanding of the role of G-quadruplex structures play in various diseases. Also, the interaction of the DNA sequence derived from the nuclear hypersensitivity element (NHE) III1 region of c-MYC oncogene (Pu22), 5'-TGAGGGTGGGTAGGGTGGGTAA-3', has added significance in that these molecules may promote or inhibit the formation of G-quadruplex DNA which could lead to the development of promising drugs for anticancer therapy. The results showed that these molecules did not disrupt G-quadruplex formation even in the absence of quadruplex-stabilizing cations. There was also evidence of concentration-dependent binding and high binding affinities based on the Stern-Volmer model, and thermodynamically favorable interactions in the form of hydrogen-bonding and interactions involving the π system of the aromatic neurotransmitters.

A structure-function study of ZraP and ZraS provides new insights into the two-component system Zra

BACKGROUND

Zra belongs to the envelope stress response (ESR) two-component systems (TCS). It is atypical because of its third periplasmic repressor partner (ZraP), in addition to its histidine kinase sensor protein (ZraS) and its response regulator (ZraR) components. Furthermore, although it is activated by Zn²⁺, it is not involved in zinc homeostasis or protection against zinc toxicity. Here, we mainly focus on ZraS but also provide information on ZraP.

METHODS

The purified periplasmic domain of ZraS and ZraP were characterized using biophysical and biochemical technics: multi-angle laser light scattering (MALLS), circular dichroism (CD), differential scanning fluorescence (DSF), inductively coupled plasma atomic emission spectroscopy (ICP-AES), cross-linking and small-angle X-ray scattering (SAXS). In-vivo experiments were carried out to determine the redox state of the cysteine residue in ZraP and the consequences for the cell of an over-activation of the Zra system.

RESULTS

We show that ZraS binds one Zn²⁺ molecule with high affinity resulting in conformational changes of the periplasmic domain, consistent with a triggering function of the metal ion. We also demonstrate that, in the periplasm, the only cysteine residue of ZraP is at least partially reduced. Using SAXS, we conclude that the previously determined X-ray structure is different from the structure in solution.

CONCLUSION

Our results allow us to propose a general mechanism for the Zra system activation and to compare it to the homologous Cpx system.

GENERAL SIGNIFICANCE

We bring new input on the so far poorly described Zra system and notably on ZraS.

Cation-induced shape programming and morphing in protein-based hydrogels

Smart materials that are capable of memorizing a temporary shape, and morph in response to a stimulus, have the potential to revolutionize medicine and robotics. Here, we introduce an innovative method to program protein hydrogels and to induce shape changes in aqueous solutions at room temperature. We demonstrate our approach using hydrogels made from serum albumin, the most abundant protein in the blood plasma, which are synthesized in a cylindrical or flower shape. These gels are then programmed into a spring or a ring shape, respectively. The programming is performed through a marked change in stiffness (of up to 17-fold), induced by adsorption of Zn2+ or Cu2+ cations. We show that these programmed biomaterials can then morph back into their original shape, as the cations diffuse outside the hydrogel material. The approach demonstrated here represents an innovative strategy to program protein-based hydrogels to behave as actuators.

Ageing, dehulling and cooking of Bambara groundnuts: consequences for mineral retention and in vitro bioaccessibility

Postharvest storage of legumes is a strategy to ensure food security. However, the hard-to-cook phenomenon, partly explained by pectin-cation-phytate theory, may develop during storage. Based on this theory, minerals could be redistributed within the matrix, affecting the concentration of free/bound minerals and hence their bioaccessibility. Therefore, this study investigated the influence of storage-induced ageing and subsequent dehulling, soaking and cooking treatments on the concentration and in vitro bioaccessibility of Ca, Mg, Fe and Zn in Bambara groundnuts. ICP-OES was performed to determine Ca, Mg, Fe and Zn concentrations after applying different treatments and after simulated digestion in the context of bioaccessibility determination. This study illustrates that while the seed coat is rich in Ca (51%), it contains only less than 15% of Mg, Fe or Zn. Hence, dehulling negatively influenced Ca, but not Mg, Fe or Zn concentration. During soaking, up to 10% or 56% of the initial Mg concentration leaches into whole or dehulled seeds, respectively. Prolonging the cooking time (300 min) of whole aged Bambara groundnuts (32 weeks), necessary for obtaining palatable textures, decreased the overall Mg, Fe and Zn concentrations by 72%, 57% and 48%, respectively. Storage-induced ageing significantly decreased Ca solubility and bioaccessibility. Bioaccessibility of trace minerals in Bambara groundnuts is low, especially for Fe, and cannot be improved by dehulling or cooking treatments. Ageing did not influence Fe and Zn bioaccessibility. Populations relying on both fresh and aged Bambara groundnuts may still be at risk for mineral deficiencies.