The three-dimensional structures of the pectic polysaccharides

The application of molecular modelling methods to the realistic description of cell wall polysaccharides is described. In a first section, the basic p rinciples and tools are presented; they provide a consistent description of the levels of structural organization of polysaccharides, from the basic m onomeric components to the more complex assemblies of macromolecular chains and their interactions. The second section provides a comprehensive illust ration which includes the application of these methods to the elucidation o f the structural features of the plant cell wall polysaccharides, pectins. The ordered and disordered states of both the 'smooth' and the 'hairy' regi ons of the pectin components are described, along with a discussion of the role of some key structural moieties such as the degree of esterification o r acetylation. The stereochemical and electrostatic requirements for ionic binding to the polysaccharide chain are also presented. In an effort to pro vide a more global view, a 'canonical' structure of pectin has been constru cted and described; it corresponds to a hypothetical model having a molecul ar mass of 50 kDa. The main structural features of rhamnogalacturonan II, w hich have been determined to date, are also reported. (C) 2000 Editions sci entifiques et medicales Elsevier SAS.