Remodeling of the Oligosaccharide Conformational Space in the Prebound State To Improve Lectin-Binding Affinity.

We developed an approach to improve the lectin-binding affinity of an oligosaccharide by remodeling its conformational space in the precomplexed state. To develop this approach, we used a Lewis X-containing oligosaccharide interacting with RSL as a model system. Using an experimentally validated molecular dynamics simulation, we designed a Lewis X analogue with an increased population of conformational species that were originally very minor but exclusively accessible to the target lectin without steric hindrance by modifying the nonreducing terminal galactose, which does not directly contact the lectin in the complex. This Lewis X mimetic showed 17 times higher affinity for the lectin than the native counterpart. Our approach, complementing the lectin-bound-state optimizations, offers an alternative strategy to create high-affinity oligosaccharides by increasing populations of on-pathway metastable conformers.

Lewis X-Carrying Neoglycolipids Evoke Selective Apoptosis in Neural Stem Cells.

N-glycans carrying the Lewis X trisaccharide [Galß1-4 (Fucα1-3) GlcNAc] are expressed by neural stem cells (NSCs) exclusively before differentiation, and they actively contribute to the maintenance of stemness of these cells. To address the functional roles of the Lewis X-mediated molecular interactions in NSCs, we created a series of synthetic neoglycolipids that contained a Lewis X-carrying glycan connected to an acyl chain through an amide bond. The neoglycolipids formed aqueous micelles displaying functional Lewis X glycotopes. Surprisingly, the neoglycolipid micelles evoked selective apoptosis in undifferentiated NSCs, whereas their differentiated cells remained unaffected. The apoptotic activity depended on the structural integrity of the Lewis X glycotopes and also on the length of the acyl chain, with an optimum length of C18. We propose hypothetical functional mechanisms of the neoglycolipid, which involves selective NSC targeting with Lewis X glycan and apoptotic signaling by the intracellular release of fatty acids. This serendipitous finding may offer a new strategy for controlling neural cell fates using artificial glycoclusters.

Hyper-Assembly of Self-Assembled Glycoclusters Mediated by Specific Carbohydrate-Carbohydrate Interactions.

Hybridization of a self-assembled, spherical complex with oligosaccharides containing Lewis X, a functional trisaccharide displayed on various cell surfaces, yielded well-defined glycoclusters. The self-assembled glycoclusters exhibited homophilic hyper-assembly in aqueous solution in a Ca2+ -dependent manner through specific carbohydrate-carbohydrate interactions, offering a structural scaffold for functional biomimetic systems.

Structural basis for two-step glucose trimming by glucosidase II involved in ER glycoprotein quality control.

The endoplasmic reticulum (ER) has a sophisticated protein quality control system for the efficient folding of newly synthesized proteins. In this system, a variety of N-linked oligosaccharides displayed on proteins serve as signals recognized by series of intracellular lectins. Glucosidase II catalyzes two-step hydrolysis at α1,3-linked glucose-glucose and glucose-mannose residues of high-mannose-type glycans to generate a quality control protein tag that is transiently expressed on glycoproteins and recognized by ER chaperones. Here we determined the crystal structures of the catalytic α subunit of glucosidase II (GIIα) complexed with two different glucosyl ligands containing the scissile bonds of first- and second-step reactions. Our structural data revealed that the nonreducing terminal disaccharide moieties of the two kinds of substrates can be accommodated in a gourd-shaped bilocular pocket, thereby providing a structural basis for substrate-binding specificity in the two-step deglucosylation catalyzed by this enzyme.

Influence of the water content on the diffusion coefficients of Li+ and water across naphthalenic based copolyimide cation-exchange membranes.

The transport of lithium ions in cation-exchange membranes based on sulfonated copolyimide membranes is reported. Diffusion coefficients of lithium are estimated as a function of the water content in membranes by using pulsed field gradient (PFG) NMR and electrical conductivity techniques. It is found that the lithium transport slightly decreases with the diminution of water for membranes with water content lying in the range 14 < λ < 26.5, where λ is the number of molecules of water per fixed sulfonate group. For λ < 14, the value of the diffusion coefficient of lithium experiences a sharp decay with the reduction of water in the membranes. The dependence of the diffusion of lithium on the humidity of the membranes calculated from conductivity data using Nernst-Planck type equations follows a trend similar to that observed by NMR. The possible explanation of the fact that the Haven ratio is higher than the unit is discussed. The diffusion of water estimated by (1)H PFG-NMR in membranes neutralized with lithium decreases as λ decreases, but the drop is sharper in the region where the decrease of the diffusion of protons of water also undergoes considerable reduction. The diffusion of lithium ions computed by full molecular dynamics is similar to that estimated by NMR. However, for membranes with medium and low concentration of water, steady state conditions are not reached in the computations and the diffusion coefficients obtained by MD simulation techniques are overestimated. The curves depicting the variation of the diffusion coefficient of water estimated by NMR and full dynamics follow parallel trends, though the values of the diffusion coefficient in the latter case are somewhat higher. The WAXS diffractograms of fully hydrated membranes exhibit the ionomer peak at q = 2.8 nm(-1), the peak being shifted to higher q as the water content of the membranes decreases. The diffractograms present additional peaks at higher q, common to wet and dry membranes, but the peaks are better resolved in the wet membranes. The ionomer peak is not detected in the diffractograms of dry membranes.