The carbohydrate glycosylphosphatidylinositol anchor chain under mechanical stress

Carbohydrates have quite complicated micro heterogenic structure which may undergo different structural transitions. Due to their extreme flexibility it is very difficult to investigate such structural changes experimentally. In these studies we want to predict what structural and conformational changes are possible in the carbohydrate glycosylphosphatidylinositol anchor chain (GPI): the tetrasaccharide with the unique sequence Man-α(1 → 2)-Man-α(1 → 6)-Man-α(1 → 4)-GlcN-α. This is a very important biomolecule associated with the processes of transmitting various types of signals in the cells of living organisms. In order to investigate conformational and structural changes in GPI we use in these studies the theoretical Enforced Geometry Optimization (EGO) method. In this method a molecule is exposed to a mechanical stress caused by external forces applied to selected atoms. It turned out that under external stretching forces the mannopyranose unit can change its ⁴C₁ chair conformation into three different forms: ¹S₃, ^oS₂ and B_2,5. The initial ⁴C₁ glucosamine ring can transit into the twisted boat ¹S₃ and the boat B_o,3 conformations. The obtained results confirm the high flexibility of the GPI anchor sugar chain.