We have determined a structure of a DNA oligonucleotide containing GGGAGCG repeats found in the regulatory region of the PLEKHG3 gene, which is connected to autism. Even though the oligonucleotide is rich in guanine residues it does not fold into a G-quadruplex. Instead of G-quartets the fold is stabilized by four G-C base pairs in Watson-Crick geometry, four G∙A base pairs in N7-N1 amino carbonyl and six G∙G base pairs in N1-carbonyl symmetric geometry. The G∙A and G-C base pairs form a cavity in the center of the structure. On each side of the structure two edgewise loops are stabilized by three G∙G base pairs in N1-carbonyl symmetric geometry. Additionally, two adenine residues not bound by H-bonds are orientated inside the structure and are tightly packed with three G∙G base pairs and two G∙A base pairs. Because the structure is not stabilized by G-quartets it folds into the final structure in the presence of Li+ cations alone. The fold was retained in the presence of Li+, Na+, K+ and NH4+ ions.
COBISS.SI-ID: 5625626
A new folding intermediate of Oxytricha nova telomeric Oxy-1.5 G-quadruplex was characterized in aqueous solution using NMR spectroscopy, native gel electrophoresis, thermal differential spectra, CD spectroscopy, and differential scanning calorimetry. NMR experiments have revealed that intermediate i-Oxy-1.5 exists in two symmetric bimolecular forms in which all guanine bases are involved in GG N1-carbonyl symmetric base pairs. Kinetic analysis of potassium ion induced structural transitions shows that folding of Oxy-1.5 G-quadruplex from i-Oxy-1.5 is much faster and proceeds through less intermediates than folding from single strands. This study provides evidence that G-rich DNA sequences can self-assemble into specific preorganized DNA structures that are predisposed to fold into G-quadruplex when interacting with cations such as potassium ions.
COBISS.SI-ID: 1701423
A multidimensional heteronuclear NMR study has demonstrated that a guanine-rich DNA oligonucleotide originating from the N-myc gene folds into G-quadruplex structures in the presence of potassium, amonium and sodium ions. A monomeric G-quadruplex formed in potassium ion containing solution exhibits three G-quartets and flexible propeller-type loops. The 3D structure with three single nucleotide loops represents a missing element in structures of parallel G-quadruplexes. The structural features together with the high temperature stability suggest specific biological role of G-quadruplex formation within the intron of the N-myc gene. An increase in potassium ion and oligonucleotide concentrations resulted in transformation of the monomeric G-quadruplex into a dimeric form. The dimeric G-quadruplex exhibits six stacked G-quartets, parallel strand orientations and propeller-type loops. A link between the third and the fourth G-quartets consists of two adenine residues that are flipped out to facilitate consecutive stacking of six G-quartets.
COBISS.SI-ID: 4920602
The influence of deodorization parameters (temperature, steam flow, time) on the phenolic content and radical scavenging effectiveness (RSE) of methanolic extracts of camelina oil was investigated and analysed by response-surface methodology (RSM). The phenolic content can be considered to be a linear function of all three parameters. A positive linear relationship between the content of phenolic compounds in deodorized oils and RSE was observed. The lack of correlation between RSE or total phenolic content with oxidative stability of the deodorized oils suggests that antioxidants in scavenging radicals react by different mechanisms, depending on radical type and reaction medium.
COBISS.SI-ID: 4278136
We presented an efficient synthesis and application of a new member of the ansa-ruthenium catalysts for asymmetric transfer hydrogenation which follows the increasingly popular trend towards structurally-rigid Ru(II) catalysts for ketone reduction. It exhibited excellent performance against a challenging class of substrates such as 1-naphthyl ketones displaying high enantioselectivity and activity. In fact, the catalyst with an substrate-to-catalyst ratio of 1000 in the presence of HCO2H/Et3N 5:2 at 40-60 °C, afforded alpha-(1-naphthyl)ethanols with up to )99.9% enentiomeric excesses and complete conversions within 6-20 h. These results are very valuable in metal-catalyzed synthesis and potentially useful for the preparation of chiral pharmaceuticals or chiral building blocks in general.
COBISS.SI-ID: 36628229