[Molecular modelling of glycans: three-dimensional structure and protein fraction interaction. The example of rabbit sero-transferrin].

On the basis of experimental data and of computer calculations using the Tripos 5.3 force field in order to examine the three-dimensional structures which are sterically feasible and the conformations which are energetically the most favourable, we have designed a program of molecular modelling of biantennary glycans of the N-acetyllactosaminic type (complex type). We demonstrate that, in absence of any interaction with the protein, a high number of glycan conformations exists which can be classified into five basic conformations, four of which have already been described. In fact, in addition to the Y-, T-, "bird" and "broken-wing" conformations, a "back-folded wing" conformation is energetically feasible. In contrast, the glycan linked to the protein is immobilized into only one conformation: the "broken-wing" conformation. Forming a bridge between the two lobes of the peptide chain, it probably contributes to the maintenance of the protein in a biologically active conformation.