Systematic conformational search for the branching point of amylopectin

A systematic modelling for the branching point of amylopectin, on the basis of the double-helical structure proposed for amylose polymorphs was performed. A 'several steps' approach was used with increasing sophistication in the refinement, combining the use of geometrical criteria and molecular mechanics calculations. This modelling leads to four groups of solutions which were compared with those existing for amylose and the related oligomers. The most stable conformations provide a minimum of deformations for the alpha(1-4) linkages adjacent to the branching point. The conformation of minimum energy roughly corresponds to the proposal of Imberty and Perez and includes an alpha(1-6) configuration compatible with the well-known calculated maps. The other possible solutions are discussed in terms of deformations for the glucopyranose rings and of unusual conformation domains for the alpha(1-6) linkage.