Mechanical Compressibility of the Glycosylphosphatidylinositol (GPI) Anchor Backbone Governed by Independent Glycosidic Linkages

About 1% of the human proteome is anchored to the outer leaflet of cell membranes via a class of glycolipids called GPI anchors. In spite of their ubiquity, experimental information about the conformational dynamics of these glycolipids is rather limited. Here, we use a variety of computer simulation techniques to elucidate the conformational flexibility of the Man-α(1→2)-Man-α(1→6)-Man-α(1→4)-GlcNAc-α-OMe tetrasaccharide backbone <b>2</b> that is an essential and invariant part of all GPI-anchors. In addition to the complete tetrasaccharide structure, all disaccharide and trisaccharide subunits of the GPI backbone have been studied as independent moieties. The extended free energy landscape as a function of the corresponding dihedral angles has been determined for each glycosidic linkage relevant for the conformational preferences of the tetrasaccharide backbone (Man-α(1→2)-Man, Man-α(1→6)­Man and Man-α(1→4)-GlcNAc). We compared the free energy landscapes obtained for the same glycosidic linkage within different oligosaccharides. This comparison reveals that the conformational properties of a linkage are primarily determined by its two connecting carbohydrate moieties, just as in the corresponding disaccharide. Furthermore, we can show that the torsions of the different glycosidic linkages within the GPI tetrasaccharide can be considered as statistically independent degrees of freedom. Using this insight, we are able to map the atomistic description to an effective, reduced model and study the response of the tetrasaccharide <b>2</b> to external forces. Even though the backbone assumes essentially a single, extended conformation in the absence of mechanical stress, it can be easily bent by forces of physiological magnitude

Triazoles: A New Class of Precursors for the Synthesis of Negatively Charged Carbon Nitride Derivatives

Carbon nitride polymers were prepared for the first time by the pyrolysis of 3,5-disubstituted-1,2,4-triazole derivatives, namely, 3,5-diamino-1,2,4-triazole [<b>1</b>] and 3-amino-1,2,4-triazole-5-thiol [<b>2</b>], in bulk as well as in LiCl/KCl salt melts. The reaction of [<b>1</b>] and [<b>2</b>] in bulk yields condensed heptazine-based polymers, while in LiCl/KCl eutectics it leads to the formation of well-defined potassium poly­(heptazine imides), according to the results of ¹³C NMR and XPS investigations, whose formation resembles that of emeraldine salts of polyaniline. The density functional calculations supported the structural model suggested for potassium poly­(heptazine imide) polymer. Owing to the specific reaction path, the products obtained from triazoles therefore show electronic properties rather different to known carbon nitrides, such as band gap and conduction and valence bands positions. With the degree of crystallinity of the reference materials, triazole-derived carbon nitrides are characterized by almost complete absence of steady photoluminescence, since charge separation and delocalization upon excitation seem to be improved. As a consequence, photocatalysts prepared from [<b>2</b>] outperform classical carbon nitrides in a model dye degradation reaction and mesoporous graphitic carbon nitride in hydrogen evolution reaction under visible light irradiation. On its turn, [<b>1</b>] can be conveniently used as a comonomer in order to prepare carbon nitrides with improved visible light absorption

Photosensitive Peptidomimetic for Light-Controlled, Reversible DNA Compaction

Light-induced DNA compaction as part of nonviral gene delivery was investigated intensively in the past years, although the bridging between the artificial light switchable compacting agents and biocompatible light insensitive compacting agents was not achieved until now. In this paper, we report on light-induced compaction and decompaction of DNA molecules in the presence of a new type of agent, a multivalent cationic peptidomimetic molecule containing a photosensitive Azo-group as a branch (Azo-PM). Azo-PM is synthesized using a solid-phase procedure during which an azobenzene unit is attached as a side chain to an oligo­(amidoamine) backbone. We show that within a certain range of concentrations and under illumination with light of appropriate wavelengths, these cationic molecules induce reversible DNA compaction/decompaction by photoisomerization of the incorporated azobenzene unit between a hydrophobic <i>trans</i>- and a hydrophilic <i>cis</i>-conformation, as characterized by dynamic light scattering and AFM measurements. In contrast to other molecular species used for invasive DNA compaction, such as widely used azobenzene containing cationic surfactant (Azo-TAB, C₄-Azo-OC_X-TMAB), the presented peptidomimetic agent appears to lead to different complexation/compaction mechanisms. An investigation of Azo-PM in close proximity to a DNA segment by means of a molecular dynamics simulation sustains a picture in which Azo-PM acts as a multivalent counterion, with its rather large cationic oligo­(amidoamine) backbone dominating the interaction with the double helix, fine-tuned or assisted by the presence and isomerization state of the Azo-moiety. However, due to its peptidomimetic backbone, Azo-PM should be far less toxic than photosensitive surfactants and might represent a starting point for a conscious design of photoswitchable, biocompatible vectors for gene delivery