Symmetric dithiodigalactoside: strategic combination of binding studies and detection of selectivity between a plant toxin and human lectins

Thioglycosides offer the advantage over O-glycosides to be resistant to hydrolysis. Based on initial evidence of this recognition ability for glycosyldisulfides by screening dynamic combinatorial libraries, we have now systematically studied dithiodigalactoside on a plant toxin (Viscum album agglutinin) and five human lectins (adhesion/growth-regulatory galectins with medical relevance e.g. in tumor progression and spread). Inhibition assays with surface-presented neoglycoprotein and in solution monitored by saturation transfer difference NMR spectroscopy, flanked by epitope mapping, as well as isothermal titration calorimetry revealed binding properties to VAA (Ka: 1560 ± 20 M-1). They were reflected by the structural model and the affinity on the level of toxin-exposed cells. In comparison, galectins were considerably less reactive, with intrafamily grading down to very minor reactivity for tandem-repeat-type galectins, as quantitated by radioassays for both domains of galectin-4. Model building indicated contact formation to be restricted to only one galactose moiety, in contrast to thiodigalactoside. The tested lycosyldisulfide exhibits selectivity between the plant toxin and the tested human lectins, and also between these proteins. Therefore, glycosyldisulfides have potential as chemical platform for inhibitor design

Origen y consecuencias de las interacciones que determinan el reconocimiento molecular entre carbohidratos y compuestos aromáticos (CH/\03C0), la reactividad en cicloadiciones de diels-alder (\03C0-\03C0) y la conformación (CH...OP) /\ua0tesis que para obtener el grado de Doctor en Ciencias Químicas, presenta Karla Elizabeth Ramírez Gualito ; asesor Gabriel Eduardo Cuevas González-Bravo

. XII, 164, [19] páginas :\ua0ilustraciones. Doctorado en Ciencias Químicas\ua0UNAM, Instituto de Química,\ua0201

Structural Characterization by NMR of a Double Phosphorylated Chimeric Peptide Vaccine for Treatment of Alzheimer’s Disease

Rational design of peptide vaccines becomes important for the treatment of some diseases such as Alzheimer’s disease (AD) and related disorders. In this study, as part of a larger effort to explore correlations of structure and activity, we attempt to characterize the doubly phosphorylated chimeric peptide vaccine targeting a hyperphosphorylated epitope of the Tau protein. The 28-mer linear chimeric peptide consists of the double phosphorylated B cell epitope Tau229-237[pThr231/pSer235] and the immunomodulatory T cell epitope Ag85B241-255 originating from the well-known antigen Ag85B of the Mycobacterium tuberculosis, linked by a four amino acid sequence -GPSL-. NMR chemical shift analysis of our construct demonstrated that the synthesized peptide is essentially unfolded with a tendency to form a β-turn due to the linker. In conclusion, the -GPSL- unit presumably connects the two parts of the vaccine without transferring any structural information from one part to the other. Therefore, the double phosphorylated epitope of the Tau peptide is flexible and accessible

Enthalpic nature of the CH/pi interaction involved in the recognition of carbohydrates by aromatic compounds, confirmed by a novel interplay of NMR, calorimetry, and theoretical calculations

10 páginas, 6 figuras, 2 tablas, 1 esquema -- PAGS nros. 18129-18138Specific interactions between molecules, including those produced by a given solute, and the surrounding solvent are essential to drive molecular recognition processes. A simple molecule such as benzene is capable of recognizing and differentiating among very similar entities, such as methyl 2,3,4,6-tetra-O-methyl-α-d-galactopyranoside (α-Me5Gal), methyl 2,3,4,6-tetra-O-methyl-β-d-galactopyranoside (β-Me5Gal), 1,2,3,4,6-penta-O-acetyl-β-d-galactopyranose (β-Ac5Gal), and methyl 2,3,4,6-tetra-O-methyl-α-d-mannopyranoside (α-Me5Man). In order to determine if these complexes are formed, the interaction energy between benzene and the different carbohydrates was determined, using Calvet microcalorimetry, as the enthalpy of solvation. These enthalpy values were −89.0 ± 2.0, −88.7 ± 5.5, −132.5 ± 6.2, and −78.8 ± 3.9 kJ mol−1 for the four complexes, respectively. Characterization of the different complexes was completed by establishing the molecular region where the interaction takes place using NMR. It was determined that β-Me5Gal is stabilized by the CH/π interaction produced by the nonpolar region of the carbohydrate on the α face. In contrast, α-Me5Man is not specifically solvated by benzene and does not present any stacking interaction. Although α-Me5Gal has a geometry similar to that of its epimer, the obtained NMR data seem to indicate that the axial methoxy group at the anomeric position increases the distance of the benzene molecules from the pyranose ring. Substitution of the methoxy groups by acetate moieties, as in β-Ac5Gal, precludes the approach of benzene to produce the CH/π interaction. In fact, the elevated stabilization energy of β-Ac5Gal is probably due to the interaction between benzene and the methyl groups of the acetyls. Therefore, methoxy and acetyl substituents have different effects on the protons of the pyranose ringThis work was supported by CONACYT through grants 49921-Q and 47679-Q, and by DGAPA-UNAM grant IN-209606. J.J.-B. Thanks “Ramón y Cajal” programme and MICINN (Spain), grant CTQ2006-10374-C02-01Peer reviewe