CHAIN CONFORMATIONAL-ANALYSIS OF BEIJERAN BY N-H MAP CALCULATIONS

Possible regular helix models of beiijeran, a new acidic heteropolysac charide consisting of a trisaccharide as a repeating unit, were invest igated. Conformational analyses of the three component disaccharides w ere first carried out by calculating their relaxed-residue energy maps with respect to the glycosidic bond rotations, Phi and Psi. A search for possible beijeran chain conformations was carried out by calculati ng the two-dimensional map of the helix parameters; n (the number of a symmetric units per a fiber repeat) and h (the axial rise per the unit ), on the basis of the Phi-Psi conformations taken from the low energy regions of each of the three energy maps. The n-h values of the helix models with low steric energies were mostly found to be around the ex perimental values (n=2 and h=1.20-1.25 nm), which may support the pres ent methodology. It was also suggested that the internal flexibility o f beijeran chain allowed it to conform in diverse helical structures, each of which were reasonably in accord with the observed n-h values. The three representative helix models were finally proposed for the be ijeran chain conformation in the crystal structure. (C) 1997 Elsevier Science Ltd. All rights reserved.