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Keywords: Calcium / Carbohydrates / Heparin / Molecular modelling / NMR spectroscopy Heparin as a polyelectrolyte may exhibit cation-territorial or site-specific binding, depending on the counterion. Thus, while Ca 2+ binds specifically, Na + or Mg 2+ do so territorially. We have explored the utility of computational methods that combine the calculation of the interaction energy potential with molecular dynamics simulation for the study of the cation interaction with 1. The computational procedure was designed in order to provide an accurate calculation of the interaction energy and to account simultaneously for the flexibility of the charged heparin side chains. This procedure was able to reproduce the behaviour of Na + , Ca 2+ , and Mg 2+ , suggesting that it was the combination of charge and size in

Chondroitin sulfate proteoglycans (CS-PG) are involved in the regulation of the central nervous system in vertebrates due to their presence on cell surfaces and in the extracellular matrix of tissues. The CS moieties are built up from repeating -4)GlcA( 1-3)GalNAc( 1-disaccharide units, partly O-sulfated at different positions. The presence of the disulfated disaccharide D-unit, GlcA2S( 1-3)GalNAc6S, in the CS moiety of the proteoglycan DSD-1-PG/phosphacan, correlates with neurite outgrowth promotion. The binding of monoclonal antibody (mAb) 473HD to DSD-1-PG, reducing neuronal stimulation, is inhibited by shark cartilage CS-D. CS-D is also recognized by two other mAbs, MO-225 and CS-56. Conformational studies were performed using NMR spectroscopy and molecular modeling on five octasaccharides isolated from shark cartilage CS-D. These octasaccharides present different binding properties toward the three mAbs. The combination of the experimental and theoretical approaches revealed that the sulfate group at position 2 of GlcA in disaccharide D and the presence of an exocyclic negative tail in disaccharides C [GlcA( 1-3)GalNAc6S] and ∆C [∆ 4,5 HexA(R1-3)GalNAc6S] are important for antibody recognition.

A suitable approach which combines nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulations have been used to study the structure and the dynamics of the glycosylphosphatidylinositol (GPI) anchor Manalphal-2Manalpha1-6Manalphal -4GlcNalpha1-6myo-inositol-1-OPO(3)-sn-1,2-dimyristoylglycerol (1) incorporated into dodecylphosphatidylcholine (DPC) micelles. The results have been compared to those previously obtained for the products obtainable from (1) after phospholipase cleavage, in aqueous solution. Relaxation and diffusion NMR experiments were used to establish the formation of stable aggregates and the insertion of (1) into the micelles. MD calculations were performed including explicit water, sodium and chloride ions and using the Particle Mesh Ewald approach for the evaluation of the electrostatic energy term. The MD predicted three dimensional structure and dynamics were substantiated by nuclear overhauser effect (NOE) measurements and relaxation data. The pseudopentasaccharide structure, which was not affected by incorporation of (1) into the micelle, showed a complex dynamic behaviour with a faster relative motion at the terminal mannopyranose unit and decreased mobility close to the micelle. This motion may be better described as an oscillation relative to the membrane rather than a folding event.

The solution three‐dimensional structure of pseudopentasaccharide 6, which constitutes the product from the GPI‐PLD cleavage of a GPI anchor, has been studied using a protocol which involves a systematic search of the conformational space around the glycosidic linkages, a thorough molecular dynamics study with explicit water molecules and a full NMR analysis study of intramolecular hydrogen bonding in solution. The results indicate that 6 exists in an extended conformation with a considerable flexibility compatible with a hinge‐like conformational motion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)