Advances in carbohydrate chemistry and biochemistry最新文献

The biological signaling properties of lectins, which are carbohydrate-binding proteins, are due to their ability to bind and cross-link multivalent glycoprotein receptors on the surface of normal and transformed cells. While the crosslinking properties of lectins with multivalent carbohydrates and glycoproteins are relatively well understood, the mechanisms of binding of lectins to multivalent glycoconjugates are less well understood. Recently, the thermodynamics of binding of lectins to synthetic clustered glycosides, a multivalent globular glycoprotein, and to linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules. Importantly, the mechanism of binding of lectins to mucins is similar to that for a variety of protein ligands binding to DNA. Recent analysis also shows that high-affinity lectin-mucin crosslinking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects which facilitate binding and subsequent complex formation including enzymology.

Starch and cellulose are the most abundant and important representatives of renewable biomass. Since the mid-19th century their properties have been changed by chemical modification for commercial and scientific purposes, and there substituted polymers have found a wide range of applications. However, the inherent polydispersity and supramolecular organization of starch and cellulose cause the products resulting from their modification to display high complexity. Chemical composition analysis of these mixtures is therefore a challenging task. Detailed knowledge on substitution patterns is fundamental for understanding structure-property relationships in modified cellulose and starch, and thus also for the improvement of reproducibility and rational design of properties. Substitution patterns resulting from kinetically or thermodynamically controlled reactions show certain preferences for the three available hydroxyl functions in (1→4)-linked glucans. Spurlin, seventy years ago, was the first to describe this in an idealized model, and nowadays this model has been extended and related to the next hierarchical levels, namely, the substituent distribution in and over the polymer chains. This structural complexity, with its implications for data interpretation, and the analytical approaches developed for its investigation are outlined in this article. Strategies and methods for the determination of the average degree of substitution (DS), monomer composition, and substitution patterns at the polymer level are presented and discussed with respect to their limitations and interpretability. Nuclear magnetic resonance spectroscopy, chromatography, capillary electrophoresis, and modern mass spectrometry (MS), including tandem MS, are the main instrumental techniques employed, in combination with appropriate sample preparation by chemical and enzymatic methods.

Fructosamine has long been considered as a key intermediate of the Maillard reaction, which to a large extent is responsible for specific aroma, taste, and color formation in thermally processed or dehydrated foods. Since the 1980s, however, as a product of the Amadori rearrangement reaction between glucose and biologically significant amines such as proteins, fructosamine has experienced a boom in biomedical research, mainly due to its relevance to pathologies in diabetes and aging. In this chapter, we assess the scope of the knowledge on and applications of fructosamine-related molecules in chemistry, food, and health sciences, as reflected mostly in publications within the past decade. Methods of fructosamine synthesis and analysis, its chemical, and biological properties, and degradation reactions, together with fructosamine-modifying and -recognizing proteins are surveyed.

This review summarizes the recent research development on vertebrate sialidase biology. Sialic acid-containing compounds play important roles in many physiological processes, including cell proliferation, apoptosis and differentiation, control of cell adhesion, immune surveillance, and clearance of plasma proteins. In this context, sialidases, the glycohydrolases that remove the terminal sialic acid at the non-reducing end of various glycoconjugates, perform an equally pivotal function. Sialidases in higher organisms are differentially expressed in cells and tissues/organs, with particular subcellular distribution and substrate specificity: they are the lysosomal (NEU1), the cytosolic (NEU2), and plasma membrane- and intracellular-associated sialidases (NEU3 and NEU4). The molecular cloning of several mammalian sialidases since 1993 has boosted research in this field. Here we summarize the results obtained since 2002, when the last general review on the molecular biology of mammalian sialidases was written. In those few years many original papers dealing with different aspects of sialidase biology have been published, highlighting the increasing relevance of these enzymes in glycobiology. Attention has also been paid to the trans-sialidases, which transfer sialic acid residues from a donor sialoconjugate to an acceptor asialo substrate. These enzymes are abundantly distributed in trypanosomes and employed to express pathogenicity, also in humans. There are structural similarities and strategic differences at the level of the active site between the mammalian sialidases and trans-sialidases. A better knowledge of these properties may permit the design of better anti-pathogen drugs.

Oligosaccharides and polysaccharides have found manifold interests in the fields of food, pharmaceuticals, and cosmetics as a result of their various specific properties. Food, sweeteners, and food ingredients constitute important sectors where oligosaccharides are used in substantial amounts. Large amounts of sucrose isomers and derivatives, as well as major amounts of fructo-oligosaccharides are commercialized in Europe and worldwide as sweeteners, prebiotics, and other uses. Increasing attention has been devoted to the sophisticated roles of oligosaccharides and glycosylated compounds at cell or membrane surfaces, and their function, as in infection and cancer proliferation. The challenge for synthetic access is obvious, and convenient approaches using cheap and readily available substrates and enzymes are discussed here. Important examples of commercialized products and recent promising developments are presented in this chapter.

This article deals with the construction, characterization, and applications of nanoparticles functionalized with carbohydrates, reviewing the state of the art and discussing perspectives on the use of these nanomaterials in the fields of glycoscience and glycotechnology. These biofunctional nanostructures, where material science, nanotechnology, and carbohydrate chemical biology meet, offer interesting potential as multivalent systems for interaction studies and for applications in the emerging area of nanomedicine. The term glyconanoparticle was coined in 2001 to denote nanoparticles constructed by "covalent" linkage of neoglycoconjugates equipped with a thiol end-group to gold. These gold glyconanoparticles, first defined as water-soluble, three-dimensional multivalent model systems based on sugar-modified gold nanoclusters presenting a glycocalix-like surface with a globular carbohydrate display, have been used as tools in carbohydrate-based interaction studies and to interfere in biological process where carbohydrates are involved. The possibility of replacing the gold inorganic core by a wide variety of materials permits access to a range of glyconanoparticles having different optical, electronic, mechanical, and magnetic properties, whose size can be modulated and whose glycocalix-like surface can be engineered to modify multivalence and insert multifunctionality.

From the authors' opinion, this chapter constitutes a modest extension of the seminal and inspiring contribution of Stowell and Lee on neoglycoconjugates published in this series [C. P. Stowell and Y. C. Lee, Adv. Carbohydr. Chem. Biochem., 37 (1980) 225-281]. The outstanding progresses achieved since then in the field of the "glycoside cluster effect" has witnessed considerable creativity in the design and synthetic strategies toward a vast array of novel carbohydrate structures and reflects the dynamic activity in the field even since the recent chapter by the Nicotra group in this series [F. Nicotra, L. Cipolla, F. Peri, B. La Ferla, and C. Radaelli, Adv. Carbohydr. Chem. Biochem., 61 (2007) 353-398]. Beyond the more classical neoglycoproteins and glycopolymers (not covered in this work) a wide range of unprecedented and often artistically beautiful multivalent and monodisperse nanostructures, termed glycodendrimers for the first time in 1993, has been created. This chapter briefly surveys the concept of multivalency involved in carbohydrate-protein interactions. The topic is also discussed in regard to recent steps undertaken in glycobiology toward identification of lead candidates using microarrays and modern analytical tools. A systematic description of glycocluster and glycodendrimer synthesis follows, starting from the simplest architectures and ending in the most complex ones. Presentation of multivalent glycostructures of intermediate size and comprising, calix[n]arene, porphyrin, cyclodextrin, peptide, and carbohydrate scaffolds, has also been intercalated to better appreciate the growing synthetic complexity involved. A subsection describing novel all-carbon-based glycoconjugates such as fullerenes and carbon nanotubes is inserted, followed by a promising strategy involving dendrons self-assembling around metal chelates. The chapter then ends with those glycodendrimers that have been prepared using commercially available dendrimers possessing varied functionalities, or systematically synthesized using either divergent or convergent strategies.