The glycosylation of the variant surface glycoproteins and procyclic acidic repetitive proteins of Trypanosoma brucei.

Trypanosoma brucei, in common with the other African trypanosomes, exhibits unusual cell-surface molecular architecture. The bloodstream form of the parasite is coated with a continuous layer of approximately five million variant surface glycoprotein (VSG) dimers that provide the parasite with a macromolecular diffusion barrier to guard against lysis by the alternative complement pathway. The procyclic form of the parasite has a more diffuse cell-surface coat made up of approximately 2.5 million copies of procyclic acidic repetitive protein (PARP). Within the VSG and PARP coats exist lower-abundance surface glycoproteins such as receptors and nutrient transporters. Both the VSG molecules and the PARP molecules are attached to the membrane via glycosylphosphatidylinositol (GPI) membrane anchors and the VSGs and one form of PARP are N-glycosylated. In this article, the structures of the N-glycans and the GPI anchors of T. brucei VSGs and PARPs are reviewed and simple models of the surfaces of bloodstream and procyclic trypomastigotes are presented.